Note: Descriptions are shown in the official language in which they were submitted.
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SUBSTITUTED QUINAZOLINES
FIELD OF THE INVENTION
This invention relates to the discovery of 3-and 5-substituted analogues of
the selective platelet
lowering agent anagrelide with reduced potential for cardiovascular side-
effects which should
lead to improved patient compliance and safety in the treatment of
myeloproliferative diseases.
More specifically, the present invention relates to certain imidazoquinazoline
derivatives which
have utility as platelet lowering agents in humans. The compounds of the
present invention
function by inhibiting megakaryocytopoeisis and hence the formation of blood
platelets.
BACKGROUND OF THE INVENTION
Anagrelide hydrochloride (Agrylin , Xagrid ) is a novel orally administered
imidazoquinazoline which selectively reduces platelet count in humans and is
used for such
purposes in the treatment of myeloproliferative diseases (MPDs), such as
essential
thrombocythemia (ET), where an elevated platelet count may put the patient at
increased
thrombotic risk. The chemical structure of anagrelide, 6,7-dichloro-1,5-
dihydroimidazo[2,1-b]-
quinazolin-2(3H)-one hydrochloride monohydrate is shown as the hydrochloride
monohydrate in the
following formula:
H
I cO HCI.H20
CI
CI ~ 3 position
Preparation of anagrelide hydrochloride was referred to in U.S. Patent Nos.
3,932,407; RE31,617
and 4,146,718.
Anagrelide is a unique, highly selective platelet lowering agent. In vitro
studies of human
megakaryocytopoiesis suggested that, in vivo, its thrombocytopenic activity
results primarily
from an inhibitory effect on megakaryocyte maturation. Anagrelide inhibited
TPO-induced
megakaryocytopoiesis in a dose-dependent manner with an estimated IC50 of -26
nM, showing it
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to be a highly potent agent. Anagrelide does not affect erythroid or
myelomonocytic
differentiation stimulated by erythropoietin or granulocyte-macrophage colony-
stimulating
factor, demonstrating the selectivity of this compound against the
megakaryocytic lineage.
The drug, which is available in both the U.S. and Europe, has proven to be of
considerable
clinical value in the treatment of myeloproliferative diseases, such as
essential thrombocythemia.
Anagrelide was shown to be effective and selective in reducing and maintaining
platelet count
close to or within the physiological range in patients with thrombocythemia
secondary to a
myeloproliferative disorder. The time to complete response, defined as a
platelet count <_
600x109/L, ranged from 4 to 12 weeks. In the majority of patients, the
platelet count can be
reduced and maintained at a dose of 1 to 3mg/day.
In early volunteer trials, the most frequently reported adverse effects AEs
other than headache
were palpitations, postural dizziness and nausea. During patient studies, the
most frequently
reported drug-related AEs were headache, palpitations, oedema/fluid retention,
nausea/vomiting,
diarrhea, dizziness and abdominal pain. These effects are all likely to arise
from the secondary,
cardiovascular pharmacology associated with anagrelide resulting from its
inhibitory effects on
human phosphodiesterase III (PDE 111). Anagrelide is a potent PDE III
inhibitor with an IC50
value of -29 nM (cf. milrinone, a classical PDE III inhibitor, IC50 = 170-350
nM). Inhibition of
myocardial PDE III leads to positive inotropy (increasing of the force of
contractions of the
heart), increased chronotropy (increase in heart rate), and peripheral
vasodilatation. Such
cardiovascular manifestations of this inhibition are typically seen with the
classical positive
inotropes, milrinone and enoximone, and exploited in the short-term acute
treatment of
congestive heart failure. However, in the treatment of a so-called silent
disease (i.e.,
asymptomatic) such as ET, the cardiovascular side-effects of palpitations and
tachycardia
associated with anagrelide limit its utility and a significant proportion of
patients - reportedly
between 25 and 50% - fail to tolerate the drug during long term treatment.
The PDE III inhibitory properties of anagrelide are quite distinct from its
platelet lowering anti-
megakaryocytic effects. Indeed studies have shown no correlation between
potency as a PDE III
inhibitor and anti-megakaryocytic effects for anagrelide and its principal
pharmacologically
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active metabolite, 3-hydroxyanagrelide (3-OH anagrelide or 3-HA, formerly
known as SPD604
or BCH24426). Surprisingly the latter was found to be over 40-fold more potent
than anagrelide
as a PDE III inhibitor. With respect to inhibition of megakaryocytopoiesis
(and therefore platelet
lowering potential) it was however no more potent than the parent drug.
Anagrelide's active
metabolite, 3-HA, is present in vivo in amounts greatly exceeding those of the
parent drug with
typical exposures being 2-3 fold greater. Thus by implication 3-OH anagrelide
is likely to be a
major contributor to the pharmacological actions of the drug.
In addition to the unwanted cardiovascular effects associated with PDE III
inhibition, the
consequent elevation of cAMP can result in an anti-aggregatory effect. While
initially this
property may appear to be beneficial in essential thrombocythemia patients
predisposed to
greater thrombotic risk, such anti-platelet effects, in excess, could have
haemorrhagic
consequences and on balance may not be desirable. Indeed the haemorrhagic
events occasionally
seen in ET patients treated with anagrelide might be due to a combination of
the anti-aggregatory
effects contributed largely by 3-OH anagrelide and an overshooting of platelet
reduction,
compounded by a synergistic interaction with aspirin that is frequently
concomitantly
administered. (In some ET patients, plasma concentrations of 3-OH anagrelide
have been shown
likely to exceed the in vitro IC50 values for inhibition of platelet
aggregation by a factor of 3).
The PDE III mediated cardiovascular side-effects associated with anagrelide
treatment mean that
many patients have to be switched to the only significant alternative therapy,
namely that with
hydroxyurea. However, this drug is a simple chemical anti-metabolite which
inhibits
ribonucleoside diphosphate reductase (RNR) with resultant profound effects on
DNA synthesis.
Ribonucleoside diphosphate reductase catalyzes the conversion of
ribonucleosides into
deoxyribonucleosides, which are the building blocks of DNA synthesis and
repair. Inhibition of
ribonucleoside diphosphate reductase explains the cytoreductive and - most
importantly - the
mutagenic effects of this compound as well as its platelet lowering action.
Hydroxyurea is thus
officially classified as a "presumed human carcinogen." As well as possessing
the potential to
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induce leukemic transformation, hydroxyurea is associated with the induction
of difficult-to-treat
leg ulcers.
Faced with this dilemma in treatment options, there is a clear need for a new
agent in the
treatment of thrombocythemia which is selective in its effects on
megakaryocytopoiesis but with
reduced or minimal side effects. While anagrelide offers some selectivity in
its mechanism of
action, the limitations to its use are those associated with cardiovascular
effects resulting from its
secondary pharmacology and contributed largely by the active metabolite of
anagrelide, 3-
hydroxyanagrelide.
The metabolism of anagrelide generally proceeds extremely rapidly, resulting
in a less than ideal
pharmacokinetic profile of the drug.. The typical half-life of anagrelide is
just 1.5 hr (2.5 hr for
the metabolite) necessitating frequent drug administration (up to 4 times per
day). This,
combined with the side-effects profile, can lead to poor patient compliance.
Furthermore,
anagrelide undergoes a large first pass effect (>50%) leading to considerable
intersubject
variation in achieved exposures and, therefore, potentially variable drug
response. Also,
exposure to the pharmacologically active metabolite varies dramatically
between patients since
its formation is dependent on CYP1A, an enzyme whose expression is highly
dependent on
exposure to inducing agents such as cigarette smoke. Overall, this may result
in the need for
careful dose titration in patients being treated with anagrelide.
US4256748 discloses a number of imidazo[2,1-b]quinazolin-2(3H)-ones which have
an
analogous structure to anagrelide and which are said to be effective in the
treatment of
thromboses resulting from their anti-aggregatory effects on blood platelets
mediated by PDE III
inhibition. However, this disclosure does not appreciate the entirely separate
anti-
megakaryocytic potential (reducing platelet numbers) which could be associated
with some
analogues.
Ideally there is a need for compounds which possess anti-megakaryocytic
activity whilst at the
same time having a reduced level of PDE III inhibitory activity and therefore
unwanted
cardiovascular effects.
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It is an aim of the present invention to overcome various disadvantages of or
to improve on the
properties of prior art compounds. Thus it is an aim of the invention to
provide an anagrelide
derivative which has improved activity and / or reduced cardiovascular
toxicity relative to prior
art compounds in the treatment of diseases for which modulation of
megakaryocytopoeisis
provides an efficacious treatment. The compounds of the present invention are
especially
beneficial because they display less inhibitory activity towards
phosphodiesterase III (PDE 111)
and yet surprisingly still retain their anti-megakarycocytic and hence
platelet lowering properties.
It is also desirable that the compounds of the present invention should have
an improved
pharmacokinetic profile to aid patient compliance and ensure consistency of
therapeutic
response. It is thus a further aim to provide compounds with a good duration
of action i.e. long
half-life in vivo. Additionally it is a further aim to provide compounds that
are available via
relatively convenient synthetic processes.
The compounds described in relation to the present invention satisfy some or
all of the above
aims.
SUMMARY OF THE INVENTION
We have found that analogues of anagrelide in which the principal site of
metabolism is blocked
by an appropriate group are likely not only to have improved pharmacokinetics
but also a better
side effect profile. This would be expected to lead to better tolerability and
improved patient
compliance enabling a broader spectrum of patients to be effectively treated.
The compounds of the present invention are surprisingly beneficial for two
reasons: they have a
dramatically lower PDE III inhibitory activity than 3-hydroxyanagrelide, yet
still retain potent
anti-megakaryocytic activity. Indeed these compounds have therapeutic indices
which are likely
to be much more favorable than that for anagrelide itself.
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In one embodiment, the present invention encompasses an anagrelide analogue
comprising a 3-,
5-, 3,3- or 5,5-substituted anagrelide compound. Thus, for example, in the 3-
substituted
derivatives, first pass metabolism to 3-hydroxyanagrelide is effectively
blocked. Surprisingly,
these compounds still show good antimegakaryocytic activity. Thus one aspect
of this invention
relates to anagrelide analogues, comprising 3-substituted derivatives, wherein
first pass
metabolism to the corresponding 3-hydroxyanagrelide is effectively blocked. In
the case of the
5-substituted compounds it is expected that a bulky group is more effective
than a smaller group.
Groups such as t-butyl and other bulky blocking groups are thus expected to be
of most utility
when substituted at the 5-position. A substituent comprising a large group at
the 5-position is
expected to sterically hinder access to the 3-position by the metabolising
cytochrome's active
site. This should inhibit formation of the cardioactive metabolite, 3-
hydroxyanagrelide.
According to one aspect of the present invention, there is provided a compound
of Formula (I) or
a pharmaceutically acceptable salt or solvate thereof.
R$ Rg
'
R N
~ N
I `If o
R6 / N
2
R5 R4 R3 R
(I)
wherein:
Ri, R2 , R3 and R4 independently represent hydrogen or a blocking group which
functions to
directly or indirectly prevent metabolic reaction at the 3- position of
substitution;
or wherein R1 and R2, and/or R3 and R4 together with the carbon to which they
are attached form
a blocking group which functions to directly or indirectly prevent metabolic
reaction at either the
3-position of substitution, the remainder of groups Ri to R4 being hydrogen;
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R5 is selected from the group comprising: fluoro, chloro, bromo and iodo;
R6 is selected from the group comprising: fluoro, chloro, bromo and iodo;
R7 and R 8 are independently selected from the group comprising: H; halo;
cyano; Ci_6 alkyl, Ci_6
haloalkyl, C1_6 alkoxy, and C1_6 haloalkoxy; and
R9 is H, Ci_6 alkyl, or a Group I metal ion;
provided always that Ri , R2, R3 and R4 are not all hydrogen, or that when one
of R1 and R2 is
methyl and R3 and R4 are hydrogen then other of Ri and R2 is not hydrogen.
In an embodiment:
Ri and R2 are independently selected from the group comprising: H; cyano; Ci_6
alkyl, SCi_6
alkyl, C2_6 alkenyl, C2_6 alkynyl, C3_8 cycloalkyl wherein said alkyl,
alkenyl, alkynyl or
cycloalkyl groups may be optionally substituted by 1 to 5 groups chosen
independently from the
group comprising: halo, hydroxyl, cyano, nitro, C1_4 alkylsulphonyl and COOH;
C1_6
hydroxyalkyl; C1_6 carboxyalkyl; and sulphide;
or Ri and R2 together with the carbon to which they are attached form a C3_8
carbocyclic ring
which may be optionally substituted by 1 to 5 groups chosen independently from
the group
comprising: halo, hydroxyl, cyano, nitro, C1_4 haloalkyl, C1_4 alkylsulphonyl
and COOH;
or Ri and R2 together represent a C2_6 alkenyl or C2_6 alkynyl group bound
through a double bond
to the ring to which it is attached and which may be optionally substituted by
one to three groups
independently selected from the group comprising: halo, hydroxyl, cyano, C1_4
haloalkyl and
COOH.
In a preferred set of compounds, Ri is an optionally substituted Ci_4 alkyl or
C3_8 cycloalkyl
group.
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In a preferred set of compounds, R2 is an optionally substituted Ci_4 alkyl
group or C3_8
cycloalkyl.
In another preferred set of compounds, Ri and R2 together form an optionally
substituted C3_8
cycloalkyl group. Most preferably this is a cyclopropyl group
Other preferred compounds are those in which at least one of Ri and R2 is -
C(H)õ(F)m or -
C(H)õ(F)m C(H)p(F)y, where m = 2 or 3, and n = (3-m); and p = 2 or 3, and q =
(3-p).
More preferably at least one of Ri and R2 is CF3 or CHF2. Most preferably, at
least one of Ri and
R2 is CF3.
In an embodiment, Ri is preferably methyl, cyclopropyl, CF3 or CHFz. More
preferably, Ri is
methyl or cyclopropyl. Most preferably, Ri is methyl. In an embodiment, R2 is
preferably
methyl, cyclopropyl, CF3 or CHF2. More preferably R2 is methyl or cyclopropyl.
Most
preferably R2 is methyl.
In an embodiment:
R3 and R4 are independently selected from the group comprising: H; cyano; Ci_6
alkyl, SCi_6
alkyl, C2_6 alkenyl, C2_6 alkynyl, C3_8 cycloalkyl wherein said alkyl,
alkenyl, alkynyl or
cycloalkyl groups may be optionally substituted by 1 to 5 groups chosen
independently from the
group comprising: halo, hydroxyl, cyano, nitro, C1_4 alkylsulphonyl and COOH;
C1_6
hydroxyalkyl; C1_6 carboxyalkyl; and sulphide;
or R3 and R4 together with the carbon to which they are attached form a C3_8
carbocyclic ring
which may be optionally substituted by 1 to 5 groups chosen independently from
the group
comprising: halo, hydroxyl, cyano, nitro, C1_4 haloalkyl, C1_4 alkylsulphonyl
and COOH;
or R3 and R4 together represent a C2_6 alkenyl or C2_6 alkynyl group bound
through a double bond
to the ring to which it is attached and which may be optionally substituted by
one to three groups
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independently selected from the group comprising: halo, hydroxyl, cyano, C1_4
haloalkyl and
COOH.
In an embodiment, R3 is H or Ci_6 alkyl. Preferably, R3 is H.
In an embodiment, R4 is H or Ci_6 alkyl. Preferably, R4 is H.
In an embodiment, R5 is preferably chloro.
In an embodiment, R6 is preferably chloro.
In an embodiment R7 is H.
In an embodiment Rg is H.
In an embodiment R9 is H. In an alternative embodiment, R9 is C1_6 alkyl and,
in this case, the
PDE III inhibiting activity is effectively eliminated. Me represents a
particularly preferred alkyl
substituent. In another alternative embodiment, R9 is a Group I metal ion and,
in this case the
compounds show significantly improved water solubility. Sodium represents a
particularly
preferred Group I metal.
In a further embodiment:
Ri and R2 are independently selected from the group comprising: H; cyano; Ci_6
alkyl, C2_6
alkenyl, C2_6 alkynyl, C3_8 cycloalkyl wherein said alkyl, alkenyl, alkynyl or
cycloalkyl groups
may be optionally substituted by 1 to 5 groups chosen independently from the
group comprising:
halo, hydroxyl, cyano, nitro, C1_4 alkylsulphonyl and COOH; C1_6 hydroxyalkyl;
C1_6
carboxyalkyl; and sulphide;
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or Ri and R2 together with the carbon to which they are attached form a C3_8
carbocyclic ring
may be optionally substituted by 1 to 5 groups chosen independently from the
group comprising:
halo, hydroxyl, cyano, nitro, C1_4 haloalkyl, C1_4 alkylsulphonyl and COOH;
or Ri and R2 together with the carbon to which they are attached represent a
C2_6 alkenyl or C2_6
alkynyl group bound through a double bond to the ring to which it is attached
and being
optionally substituted by one to three groups independently selected from the
group comprising:
halo, hydroxyl, cyano, C1_4 haloalkyl and COOH;
provided always that Ri and R2 are not both hydrogen, or that when one of Ri
and R2 is methyl
the other is not hydrogen;
R3 and R4 are hydrogen;
R5 is selected from the group comprising: fluoro, chloro, bromo and iodo;
R6 is selected from the group comprising: fluoro, chloro, bromo and iodo; and
R7 , Rg and R9 are hydrogen.
Another preferred group of compounds is those in which neither Ri nor R2 is
hydrogen.
Amongst these, it is preferred when Ri and R2 are both independently selected
from the group
comprising: cyano, C1_6 alkyl, C2_6 alkenyl, C2_6 alkynyl, in which the alkyl,
alkenyl, and alkynyl
groups may be optionally substituted;
or wherein Ri and R2 together with the carbon to which they are attached form
an optionally
substituted C3_8 carbocyclic ring
or wherein Ri and R2 together represent an optionally substituted C2_6 alkenyl
or C2_6 alkynyl
group.
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Particularly preferred individual compounds of the invention include:
3-methyleneanagrelide
3,3, spiro-cyclopropyl-anagrelide
3,3-dimethylanagrelide
(R)-3-(hydroxymethyl)anagrelide
(S)-3-(hydroxymethyl)anagrelide
Particularly preferred compounds include 3,3-dimethylanagrelide, and
spiro[anagrelide-3,1'-
cyclopropane] }. These compounds are generally prepared as the HBr addition
salts.
It has also been found that the individual enantiomers of 3-substituted
derivatives show efficacy.
The present invention therefore also relates to both the resolved optical
isomers of such
compounds as well as mixtures of enantiomers. For the purposes of comparison
of the
compounds of the present invention with anagrelide, the correct comparison is
that made with
the PDE III inhibitory activity of the 3-hydroxy metabolite of anagrelide
since this is the
predominant component in plasma after anagrelide treatment.
Regarding the use of the compounds of the invention in humans, there is
provided:
a pharmaceutical composition comprising a compound of formula (I), or a
pharmaceutically
acceptable salt or solvate thereof, together with a pharmaceutically
acceptable diluent or carrier,
which may be adapted for oral, parenteral or topical administration;
a compound of formula (I), or a pharmaceutically acceptable salt or solvate
thereof, or a
pharmaceutical composition containing any of the foregoing, for use as a
medicament;
the use of a compound of formula (I), or a pharmaceutically acceptable salt or
solvate thereof in
the manufacture of a medicament for the treatment of a disease selected from:
myeloprolific
diseases and/or generalised thrombotic diseases.
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a method of treating a disease selected from: myeloproliferative diseases
and/or generalised
thrombotic diseases in a human, which comprises treating said human with an
effective amount
of a compound of formula (I), or a pharmaceutically acceptable salt or solvate
thereof, or with a
pharmaceutical composition containing any of the foregoing.
The present invention also encompasses a method of treating a patient having
essential
thrombocythemia or high blood platelet count, which method comprises
administering to the
patient a therapeutically effective amount of a compound of the present
invention.
Another embodiment of the present invention includes a method of reducing
blood platelet count
within a patient, which method comprises administering to the patient a
therapeutically effective
amount of a compound of the present invention.
The present invention encompasses providing the compounds of the present
invention for the
methods listed above, among others, wherein cardiotoxicity is reduced compared
to using
anagrelide.
Separately, we have found that individually both (R)-3-methyl anagrelide and
(S)-3-methyl
anagrelide show good anti-megakaryocytic activity whilst showing significantly
reduced PDE III
inhibition relative to 3-OH anagrelide. We thus expect that 3-methyl
anagrelide will have utility
in treating myeloproliferative diseases.
Accordingly, the invention also includes the use of 3-methyl anagrelide, or a
pharmaceutically
acceptable salt or solvate thereof in the manufacture of a medicament for the
treatment of
myeloprolific diseases.
The invention thus also extends to a method of treating myeloproliferative
diseases in a human,
which comprises treating said human with an effective amount of 3-methyl
anagrelide, or a
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pharmaceutically acceptable salt or solvate thereof, or with a pharmaceutical
composition
containing any of the foregoing.
The present invention also encompasses pharmaceutical compositions comprising
a compound or
pharmaceutically acceptable salt of a compound of the present invention and a
pharmaceutically
acceptable carrier.
DETAILED DESCRIPTION OF THE INVENTION
The present invention is directed to new 3 or 5-substituted analogues of the
established
platelet lowering agent anagrelide. Substitution at the 3 or the adjacent 5-
position of the
anagrelide molecule would be expected to block or hinder the principal site of
metabolism and
potentially preclude the formation of the highly potent PDE III inhibitor 3-OH
anagrelide while
substitution at the 1-position has surprisingly been found to abolish PDE III
inhibition. The
compounds of the present invention retain the anti-megakaryocytic properties
(hence platelet
lowering activity) of the parent drug molecule but have reduced PDE III
inhibitory properties
and hence lower potential for unwanted cardiovascular and anti-aggregatory
side-effects. They
also have the potential for improved pharmacokinetic characteristics as the
result of inhibition of
metabolism.
These improved cardiovascular and pharmacokinetic properties were demonstrated
by studies in
the dog. A comparison of the in vivo cardiovascular effects of anagrelide, its
active metabolite
and a representative example of an improved analogue shown in the table below:-
Comparative activity of anagrelide, its metabolite 3-hydroxy anagrelide and a
representative 3-
alkyl substituted analogue of the drug
Compound In vitro IC50 for In vivo ED50 for In vivo ED20 for In vitro IC50 for
PDE III inhibition effects on dog effects on dog anti-
(human enzyme) heart rate heart rate megakaryocytic
effects
(human cell-line)
Anagrelide 29nM 986 /k 376 /k 26nM
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3-hydroxy
anagrelide (active 0.7nM 11.72ug/kg 7.1 g/kg 44nM
metabolite)
3,3 dimethyl
anagelide 164nM 3,557ug/kg 2,512 g/kg 166nM
The most meaningful comparison of the data cited in the table above is between
3-hydroxy
anagrelide - as the drug's active metabolite - and the 3-alkyl substituted
analogue since the
former is the predominant species present in the plasma of patients treated
with the drug. On this
basis the therapeutic benefit to potential for CV side effects ratio is
clearly much improved for
this 3-alkyl derivative.
A comparison of the pharmacokinetic profile in the dog of anagrelide and a
representative 3-
substituted analogue is shown below:-
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Comparative pharmacokinetics of anagrelide, its resultant active metabolite
and a representative 3-
substituted analogue follow 1 mg/kg iv in the conscious dog model
Compound CmaX AUC(o_t) T12 CL* V..* F(AUCO-t))*
(ng/mL) (ng.h/mL) (h) (mL/h/kg) (mL/kg)
Anagrelide 48.1 21 101 15 1.37 20 1156 4.56 1011 3.8 11.8 14.4
3-hydroxy
anagrelide
(arising 60.1 14 179 14 1.57 24 NA NA
from
anagrelide
treatment)
3,3 167 33 1903 47 9.39 21 178 45.9 1967 24 39 25
dimethyl
anagelide
Results represent geometric means and % CV
* After 1 mg/kg iv
The data in the above table clearly show a much longer half-life for the 3-
alkyl substituted
analogue compared to anagrelide itself (9.39 vs 1.37h) which, if reflected in
man, should enable
much less frequent drug administration and improved patient compliance
compared to that seen
with anagrelide. This comparatively longer half-life for 3,3 dimethyl
anagrelide observed in the
dog was mirrored in an in vitro metabolic stability study in which it was
clearly much more
metabolically stable than anagrelide (see table below). Hepatic metabolism is
known to be the
principal mechanism of clearance of anagrelide in both animals and in man.
Furthermore, and
most importantly, this much greater metabolic stability for the 3-substituted
analogue was also
observed in human hepatocytes suggesting the likelihood of improved
pharmacokinetics in man.
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Comparative metabolic stability of anagrelide and a representative analogue in
dog and human
hepatocytes
Compound In vitro "half-life" in In vitro "half-life" in
dog hepatocytes human hepatocytes
Anagrelide 1.25h 6.62h
3,3 dimethyl anagrelide No apparent degradation over 22.8h
time course of study
The pharmaceutically acceptable acid addition salts of certain of the
compounds of formula (I)
may also be prepared in a conventional manner. For example, a solution of the
free base is
treated with the appropriate acid, either neat or in a suitable solvent, and
the resulting salt
isolated either by filtration or by evaporation under reduced pressure of the
reaction solvent. For
a review on suitable salts, see "Handbook of Pharmaceutical Salts: Properties,
Selection, and
Use" by Stahl and Wermuth (Wiley-VCH, Weinheim, Germany, 2002).
Definition of terms:-
Halo means a group selected from: fluoro, chloro, bromo or iodo.
The term "alkyl" as used herein as a group or a part of a group refers to a
straight or branched
hydrocarbon chain containing the specified number of carbon atoms. For
example, Ci_io alkyl
means a straight or branched alkyl containing at least 1 and at most 10 carbon
atoms. Examples
of "alkyl" as used herein include, but are not limited to, methyl, ethyl, n-
propyl, n-butyl, n-
penryl, isobutyl, isopropyl, t-butyl, hexyl, heptyl, octyl, nonyl and decyl. A
C1_4 alkyl group is
one embodiment, for example methyl, ethyl, n-propyl, isopropyl, n-butyl,
isobutyl or t-butyl.
The term "cycloalkyl" as used herein refers to a non-aromatic monocyclic
hydrocarbon ring of 3
to 8 carbon atoms such as, for example, but not limited to, cyclopropyl,
cyclobutyl, cyclopentyl,
cyclohexyl or cycloheptyl.
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The term "spirocyclic" as used herein refers to a ring system joined to a
second ring system at
one carbon atom.
The term "alkoxy" as used herein refers to a straight or branched hydrocarbon
chain group
containing oxygen and the specified number of carbon atoms. For example, C1_6
alkoxy means a
straight or branched alkoxy containing at least 1 and at most 6 carbon atoms.
Examples of
"alkoxy" as used herein include, but are not limited to, methoxy, ethoxy,
propoxy, prop-2-oxy,
butoxy, but-2-oxy, 2-methylprop-l-oxy, 2-methylprop-2-oxy, pentoxy and
hexyloxy. A C1_4
alkoxy group is one embodiment, for example methoxy, ethoxy, propoxy, prop-2-
oxy, butoxy,
but-2-oxy or 2-methylprop-2-oxy.
The term "hydroxyalkyl" as used herein as a group refers to a straight or
branched hydrocarbon
chain containing the specified number of carbon atoms, which is substituted by
1-3 hydroxyl
groups. For example, C1_4 hydroxyalkyl means a straight or branched alkyl
chain containing from
1 to 4 carbon atoms and at least one hydroxyl group; examples of such group
include
hydroxymethyl, hydroxyethyl, hydroxypropyl, hydroxyisopropyl, hydroxybutyl and
the like.
The term "alkenyl" as used herein as a group or a part of a group refers to a
straight or branched
hydrocarbon chain containing the specified number of carbon atoms and
containing at least one
double bond. For example, the term "C2_6 alkenyl" means a straight or branched
alkenyl
containing at least 2 and at most 6 carbon atoms and containing at least one
double bond.
Examples of "alkenyl" as used herein include, but are not limited to, ethenyl,
2-propenyl, 3-
butenyl, 2-butenyl, 2-pentenyl, 3-pentenyl, 3-methyl-2-butenyl, 3-methylbut-2-
enyl, 3-hexenyl
and 1,1-dimethylbut-2-enyl. It will be appreciated that in groups of the form -
O-C2_6 alkenyl, the
double bond is preferably not adjacent to the oxygen.
The term "alkynyl" as used herein as a group or a part of a group refers to a
straight or branched
hydrocarbon chain containing the specified number of carbon atoms and
containing at least one
triple bond. For example, the term "C2_6 alkynyl" means a straight or branched
alkynyl
containing at least 2 and at most 6 carbon atoms and containing at least one
triple bond.
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Examples of "alkynyl" as used herein include, but are not limited to, ethynyl,
2-propynyl, 3-
butynyl, 2-butynyl, 2-pentynyl, 3-penrynyl, 3-methyl-2-burynyl, 3-methylbut-2-
ynyl, 3-
hexynyl and 1,1-dimethylbut-2-ynyl. It will be appreciated that in groups of
the form
-O-C2-6 alkynyl, the triple bond is preferably not adjacent to the oxygen. The
term "halo"
refers to halogens such as fluorine, chlorine, bromine or iodine atoms.
The term "sulfide" refers to a radical of Ra S-Rb, wherein a sulfur atom is
covalently attached to
two hydrocarbon chains, Ra and Rb, wherein the two hydrocarbon chains may be,
for example,
but not limited to, any discussed above.
The compounds of the invention, i.e. those of formula (I), possess
antimegakaryocytic activity in
humans. They may be particularly useful in the treatment of myeloprolific
diseases. The
compounds may also find utility in the treatment of generalised thrombotic
diseases.
It is to be appreciated that references to treatment include prophylaxis as
well as the alleviation
of established symptoms of a condition. "Treating" or "treatment" of a state,
disorder or
condition includes: (1) preventing or delaying the appearance of clinical
symptoms of the state,
disorder or condition developing in a human that may be afflicted with or
predisposed to the
state, disorder or condition but does not yet experience or display clinical
or subclinical
symptoms of the state, disorder or condition, (2) inhibiting the state,
disorder or condition, i.e.,
arresting, reducing or delaying the development of the disease or a relapse
thereof (in case of
maintenance treatment) or at least one clinical or subclinical symptom
thereof, or (3) relieving or
attenuating the disease, i.e., causing regression of the state, disorder or
condition or at least one
of its clinical or subclinical symptoms.
Myeloproliferative diseases which may be treatable with the compounds of the
present invention
include: essential thrombocythemia, polycythema vera, chronic idiopathic
myelofibrosis, chronic
myeloid leukaemia with residual thrombocytosis, reactive thrombocytosis
immediately
preceding a surgical procedures, as an immediate or post operative
preventative measures to
minimise the risk of thrombus formation during or post surgery.
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Thrombotic cardiovascular diseases (TCVD) (i.e. patients at increased
generalised thrombotic
risk) which may also be treatable with the compounds of the present invention
include:
myocardial infarct (heart attack) thrombotic stroke, patients having undergone
coronary stent
placement.
The compounds of the present invention may find utility for the reduction of
atherothrombotic
events as follows: recent MI, recent stroke or established peripheral arterial
disease, acute
coronary syndrome (unstable angina/non-Qwave MI), cardiovascular death, MI,
stroke, and
refractory ischemia.
It is to be understood that compounds of formula (I) may contain one or more
asymmetric carbon
atoms, thus compounds of the invention can exist as two or more stereoisomers.
Included within the scope of the present invention are all stereoisomers such
as enantiomers and
diastereomers, all geometric isomers and tautomeric forms of the compounds of
formula (I),
including compounds exhibiting more than one type of isomerism, and mixtures
of one or more
thereof.
Solubility studies were carried out on a number of anagrelide derivatives
according to the present
invention in various test media. The test media were:
a) singly distilled water (pH 5.0) - note no attempt was made to remove
dissolved COz.
b) 50 mM ammonium formate (pH 7.9)
c) 0.1 M hydrochloric acid (pH 0.6)
Calibration plots of HPLC peak area vs. concentration were obtained in MeOH or
MeOH /
DMSO over the range 1000 - 1 g / ml for each substance at a temperature 20 -
22 C. The
HPLC method used a reverse phase C18 column with a water (0.6% formic acid)
and acetonitrile
gradient. For the solubility studies, saturated solutions were prepared by
dissolving in the desired
medium with the aid of an ultrasonic bath for 20 minutes and the excess solid
removed by
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WO 2008/065444 PCT/GB2007/050697
centrifugation. The concentration of the substance in the supernatant liquid
was determined from
the measured peak area.
Unexpectedly it was found that stable metal salts could be prepared following
deprotonation at
the 1-position of the quinazoline ring structure. The value of such salts is
seen in their relatively
much greater aqueous solubility than the corresponding HBr salts. This is
likely to facilitate the
rapid dissolution and quantitative absorption of these generally poorly water
soluble compounds
and so represent a major clinical advantage. These salts are Group I metal
salts and most
usually are sodium or potassium salts. Table 1 shows the results of the
solubility measurements.
Table 1
Solubilities of Anagrelide and Anagrelide Derivatives ( g mL"i at ca. 20 C)
Compound Ammonium formate Water Hydrochloric acid
(50 mM, pH 7.9) (pH 5.0) (0.1 M, pH 0.6)
Anagrelide 10 11 169
hydrochloride
3,3- 6 409 212
Dimethylanagrelide
sodium salt
3,3- 4 20 215
Dimethylanagrelide
hydrobromide
3,3,Spiro- 1 542 28
Cyclopropyl-
anagrelide sodium salt
3,3-spiro- 1 2 35
Cyclopropyl-
anagrelide
hydrobromide
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3- 5 9 43
Methyleneanagrelide
3- 39 1830 189
Methyleneanagrelide
Na salt
Geometric isomers may be separated by conventional techniques well known to
those skilled in
the art, for example, by chromatography and fractional crystallisation.
Stereoisomers may be separated by conventional techniques known to those
skilled in the art -
see, for example, "Stereochemistry of Organic Compounds" by E L Eliel (Wiley,
New York,
1994).
The compounds of formula I can be prepared using literature techniques and in
an analogous
manner to those described in Formula Scheme I and Formula Scheme 11 in US
4256748. The
synthesis of 3-ethyl anagrelide is described by way of example to show how
individual isomers
of the invention can be prepared. Analogous procedures can be used to prepare
the other
compounds of the invention by using appropriate a-haloesters
The formation of 3-ethyl anagrelide (compound (4a)) is shown in Scheme A
below. 1-amino-2,
3-dichloro nitrobenzene (1a) undergoes nucleophilic substitution with the a-
haloester R-ethyl-2-
bromobutanoate to afford compound (2a). The nitro group is then reduced to an
amine group
using tin chloride in ethanol to afford the diamine compound (3a). Compound
(3a) is then
cyclised with cyanogen bromide in toluene to yield the 3-ethyl anagrelide
(4a).
Scheme A: Formation of 3-ethylanagrelide.
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Br R CO2Et
N02 N02
Et
CI NH2 CI N s CO2Et
CI (1a) ci (2a) Et
H
~ NH2 N
SnCl2 I H CNBr ):?c O
EtOH CI ~ NsC02Et Toluene CI N s
CI (3a) Et CI (4a) Et
The formation of certain derivatives is accomplished in an analogous manner to
the synthesis
shown in Scheme A above or by reversing the positions of the NH2 group and the
Br groups in
the starting materials, as appropriate to the chemistry involved. In this
case, an a-aminoester and
a halobenzyl derivative are used as the starting materials. The reaction can
be generically
presented as shown in Scheme B below in relation to the 3-substituted
compound.
Scheme B: Formation of 3-substituted anagrelides.
B CO2Et
NO2 N02
R
CI I/ A CI N C02Et
I
CI CI R
H
NH2 NN
SnCl2 H CNBr I O
EtOH CI N~C02Et Toluene CI N
CI R CI
where A is NH2 or Br, and B is the other of NH2 or Br
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The formation of (R)-3-ethyl anagrelide can be accomplished in an analogus
manner to the
synthesis shown in Scheme A above. In this case an a-haloester of the opposite
stereochemistry
to that used in Scheme A is employed in the nucleophilic substitution step
i.e. S-ethyl-2-
bromobutanonate. This procedure is generally applicable.
If single enantiomers are not required then a racemic a-haloester can be
employed in the first
stage of the synthesis.
A person skilled in the art will be aware of variations of, and alternatives
to, the processes
referred to above and to those in US 4256748 which allow the individual
compounds defined by
formula (I) to be obtained.
It will also be appreciated by a person skilled in the art that the compounds
of the invention
could be made by adaptation of the methods herein described and/or adaptation
of methods
known in the art, for example the art described herein, or using standard
textbooks such as
"Comprehensive Organic Transformations - A Guide to Functional Group
Transformations", RC
Larock, Wiley-VCH (1999 or later editions), "March's Advanced Organic
Chemistry - Reactions,
Mechanisms and Structure", MB Smith, J. March, Wiley, (5th edition or later)
"Advanced
Organic Chemistry, Part B, Reactions and Synthesis", FA Carey, RJ Sundberg,
Kluwer
Academic/Plenum Publications, (2001 or later editions), "Organic Synthesis -
The Disconnection
Approach", S Warren (Wiley), (1982 or later editions), "Designing Organic
Syntheses" S Warren
(Wiley) (1983 or later editions), "Guidebook To Organic Synthesis" RK Mackie
and DM Smith
(Longman) (1982 or later editions), etc.,and the references therein as a
guide.
It will also be apparent to a person skilled in the art that sensitive
functional groups may need to
be protected and deprotected during synthesis of a compound of the invention.
This may be
achieved by conventional methods, for example as described in "Protective
Groups in Organic
Synthesis" by TW Greene and PGM Wuts, John Wiley & Sons Inc (1999), and
references
therein.
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Compounds of the invention intended for pharmaceutical use may be administered
as crystalline
or amorphous products. They may be obtained, for example, as solid plugs,
powders, or films by
methods such as precipitation, crystallization, freeze drying, or spray
drying, or evaporative
drying. Microwave or radio frequency drying may be used for this purpose.
They may be administered alone or in combination with one or more other
compounds of the
invention or in combination with one or more other drugs. Generally, they will
be administered
as a formulation in association with one or more pharmaceutically acceptable
excipients.
Pharmaceutically acceptable excipients include one or more of: anti-oxidants,
colourants,
flavouring agents, preservatives and taste-masking agents.
Pharmaceutical compositions suitable for the delivery of compounds of the
present invention and
methods for their preparation will be readily apparent to those skilled in the
art. Such
compositions and methods for their preparation may be found, for example, in
`Remington's
Pharmaceutical Sciences', 19th Edition (Mack Publishing Company, 1995). The
formulation of
tablets is discussed in "Pharmaceutical Dosage Forms: Tablets, Vol. 1", by H.
Lieberman and L.
Lachman, Marcel Dekker, N.Y., N.Y., 1980 (ISBN 0-8247-6918-X).
The methods by which the compounds may be administered include oral
administration by
capsule, bolus, tablet, powders, lozenges, chews, multi and nanoparticulates,
gels, solid solution,
films, sprays, or liquid formulation. Liquid forms include suspensions,
solutions, and syrups.
Such formulations may be employed as fillers in soft or hard capsules and
typically comprise a
carrier, for example, water, ethanol, polyethylene glycol, propylene glycol,
methylcellulose, or a
suitable oil, and one or more emulsifying agents and/or suspending agents.
Liquid formulations
may also be prepared by the reconstitution of a solid preparation, for
example, from a sachet.
The compounds may also be administered topically to the skin or mucosa, that
is dermally or
transdermally. Typical formulations for this purpose include pour-on
solutions, sprays, powder
formulations, gels, hydrogels, lotions, creams, ointments, films and patches,
and implants.
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The compounds can also be administered parenterally, or by injection directly
into the blood
stream, muscle or into an internal organ. Suitable means for parenteral
administration include
intravenous, intraarterial, intraperitoneal, intrathecal, intraventricular,
intraurethral, intrasternal,
intracranial, intramuscular and subcutaneous. Suitable devices for parenteral
administration
include needle (including microneedle) injectors, needle-free injectors and
infusion techniques.
Formulations may be immediate and/or modified controlled release. Controlled
release
formulations include Modified release formulations include: delayed-,
sustained-, and pulsed-
release.
Dosages
Typically, a physician will determine the actual dosage which will be most
suitable for an
individual subject. The specific dose level and frequency of dosage for any
particular individual
may be varied and will depend upon a variety of factors including the activity
of the specific
compound employed, the metabolic stability and length of action of that
compound, the age,
body weight, general health, sex, diet, mode and time of administration, rate
of excretion, drug
combination, the severity of the particular condition, and the individual
undergoing therapy.
In general however a suitable dose will be in the range of from about 0.001 to
about 50 mg/kg of
body weight per day, in a further embodiment, of from about 0.001 to about 5
mg/kg of body
weight per day; in a further embodiment of from about 0.001 to about 0.5 mg/kg
of body weight
per day and in yet a further embodiment of from about 0.001 to about 0.1mg/kg
of body weight
per day. In further embodiments, the ranges can be of from about 0.1 to about
750 mg/kg of body
weight per day, in the range of 0.5 to 60 mg/kg/day, and in the range of 1 to
20 mg/kg/day.
The desired dose may conveniently be presented in a single dose or as divided
doses
administered at appropriate intervals, for example as one, two, three, four or
more doses per day.
If the compounds are administered transdermally or in extended release form,
the compounds
could be dosed once a day or less.
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The compound is conveniently administered in unit dosage form; for example
containing 0.1 to
50 mg, conveniently 0.1 to 5 mg, most conveniently 0.1 to 5 mg of active
ingredient per unit
dosage form. In yet a further embodiment, the compound can conveniently
administered in unit
dosage form; for example containing 10 to 1500 mg, 20 to 1000 mg, or 50 to 700
mg of active
ingredient per unit dosage form.
Compounds of the present invention and their activities are exemplified below.
Example 1
Comparative IC5o data on anagrelide and some 3-alkyl substituted analogues as
PDE III
inhibitors and anti-megakaryocytic agents
The table below shows the comparative activity of anagrelide and its analogues
with respect to
their effects on megakaryocytopoeisis (the process giving rise to blood
platelets) and PDE III
(inhibition of which leads to adverse cardiovascular responses).
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Comparative in vitro assessment of potential therapeutic and adverse effects
of anagrelide and its
analogues
Compound IC50 for anti- IC50 for PDE III Benefit ratio
megakaryocytic inhibition (therapeutic to
(platelet lowering) (cardiovascular adverse effects)
activity effects)
Anagrelide 27nM 32nM *0.024: 1
3-hydroxy 44nM 0.7nM 0.016:1
anagrelide
3,3 dimethyl 164nM 166nM 1: 1
anagrelide
3-spirocyclo 547nM 797nM 1.45:1
propyl anagrelide
* Pharmacokinetically adjusted value based on three-fold greater systemic
exposure to active
metabolite (3-hydroxy anagrelide) than to the drug itself in man.
Assessment of the in vitro anti-megakaryocytic activity - and potentially
therefore the platelet
lowering capability - of the 3-substituted analogues of anagrelide was
conducted using a well
established model of megakaryocytopoiesis (Cohen-Solal et al., Thromb.
Haemost. 1997, 78:37-
41 and Cramer et al., Blood, 1997, 89:2336-46). It can be readily seen that
with anagrelide the
benefit ratio (therapeutic to adverse effects) was comparatively low at
0.024:1 (after accounting
for the predominant exposure to the cardioactive metabolite in vivo). By
contrast 3-
spirocyclopropyl and 3,3 dimethyl anagrelide both demonstrated a relatively
much better benefit
ratio in these studies.
27
