Chemistry Reference
In-Depth Information
O
OH
OH
H
H
O
O
O
O
H
H
H
H
H
H
H
H
OH
OH
OH
O
8
7
O
O
O
7
O
7
H
H
Me
H
H
H
H
H
H
H
H
Me
Me
Me
Me
i
n vivo
2
′
N
N
N
N
N
5
′
34
35
36
37
33
CF
3
CF
3
CF
3
CF
3
CF
3
Figure 2.8
Major metabolites of compound 33.
2.4.4.1.3 Identification of a Metabolism-based Second-generation Thrombin
Receptor Antagonist. Metabolite profiling of [
3
H]-33 done in rat hepato-
cytes indicated three monohydroxylated and multiple dihydroxylated meta-
bolites, according to mass spectral characterization (Figure 2.8).
65
Quantities
of metabolites needed for NMR characterization were initially generated by
incubation of the parent compound with pregnenolone 16a-carbonitrile
(PCN)-induced rat liver microsomes. NMR studies indicated that the major
metabolite was the 8b-OH compound 34, and that the minor metabolites
were 7a- and 7b-hydroxy derivatives 35 and 36, respectively. In cynomolgus
monkeys, a similar pattern of metabolites was seen after oral administration
of the compound and analysis of plasma samples withdrawn at 6 and 24 h
time points.
In a multiple rising-dose study in rat over a 10-day period, compound 33
(300mg kg
1
) induced a very high elevation (21-fold) of rat-specific cytochrome
P4502B (CYP2B) isozyme and considerable elevation of CYP1A (3.6-fold).
Additionally, there was a concomitant reduction of the plasma concentration
of the parent drug from day one to day eight, suggesting an auto-induction/
metabolism pattern. Since this profile would make it di
cult to sustain high
levels of the parent in the plasma in the rodent species required for long-term
toxicological studies, this compound was dropped from further consideration
for development.
The mono-oxygenated metabolites of 33 were evaluated as potential repla-
cement candidates.
65
The syntheses of these compounds were carried out in a
fashion similar to the original synthesis, but using preinstalled ketal groups at
the carbons that would eventually bear the hydroxyl groups (Scheme 2.3). The
7a- and 7b-hydroxy derivatives showed comparable IC
50
values. The 8-hydroxy
analogs were slightly less active.
In the ex vivo platelet aggregation inhibition assay model in cynomolgus
monkeys, compounds 35 (a-OH) and 36 (b-OH) showed equivalent potency:
both exhibited robust inhibition of platelet aggregation after an oral adminis-
tration of 1mg kg
1
, with complete suppression of platelet aggregation at
earlier time points and
60% inhibition at the 24-h time point.
65
However, the
b-OH isomer showed interconversion to the a-OH isomer in cynomolgus
monkeys. This interconversion was also observed in monkey and human
B
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