A.G. Waterson et al.
Bioorganic&MedicinalChemistryLettersxxx(xxxx)xxx–xxx
Table 1
Structures and PLD activities of (S)-and (R)-14 and (S)-and (R)-16.
Compound
R
1200
70
(S)-14a
(R)-14a
(S)-16a
(R)-16a
6400
16
810
Scheme 1. Synthesis of 4-fluorophenyl 2,8-diazaspiro[4.5]decanone cores 12.a
aReagents and conditions. (a) trans-1-fluoro-4-(2-nitrovinyl)benzene, LDA, THF,
−40 °C, 2 h, 90%; (b) H2, Ra-Ni, EtOH, 50 °C, 20 h, 86%; (c) i) toluene, reflux;
ii) Boc2O, DIPEA, dioxane-H2O, 0 °C, 2 h, 83%; d) i) Gilson 215 Preparative
150
320
4000
HPLC with pumps capable of 200 mL/min using
a Chiraltech OJ 20u,
50 × 250 mm column at a flow rate of 177 mL/min (95% hexanes and 5%
(S)-14b
(R)-14b
(S)-16b
(R)-16b
21
320
1
2.5
43
isopropyl alcohol. (S)-12 is first eluting peak; ii) TFA, CH2Cl2, rt, 5 h, 95%.
12
16
140
(S)-14c
(R)-14c
(S)-16c
(R)-16c
(S)-14d
(R)-14d
(S)-16d
(R)-16d
(S)-16e
1350
12,000
25
60
450
115
700
220
3175
210
2800
26
Scheme 2. Synthesis of 2,8-diazaspiro[4.5]decanone-based PLD inhibitors 14.a
aReagents and conditions: (a) i) tert-butyl 2-oxoethylcarbamate, MPB(OAc)3H,
DCM, rt; ii) 4.0 M HCl/dioxane, DCM, MeOH, rt, 79–85%; (b) RCOCl, DIEA,
DMF, rt, 58–95%.
200
5500
> 20,000
250
1700
820
Scheme 3. Synthesis of 2,8-diazaspiro[4.5]decanone-based PLD inhibitors 16.a
aReagents and conditions: (a) i) (S)-tert-butyl 1-oxo-2-propanylcarbamate, MPB
(OAc)3H, DCM, rt; ii) 4.0 M HCl/dioxane, DCM, MeOH, rt, 70–82%; (b) RCOCl,
DIEA, DMF, rt, 55–92%.
bPLD2 cellular assay in HEK293-gfp-PLD2 cells. IC50 values are the average of
three independent measures (n = 3).
a
Cellular PLD1 assay in Calu-1 cells.
pairs of (S)- and (R)-14 derivatives. Thus, further optimization will
maintain the (S)-configuration at the aryl bearing stereogenic center.
The SAR trend within 3–6 by which a chiral (S)-methyl moiety on the
linker not only improved PLD activity, but also enhanced PLD1 in-
hibitory activity was retained in the diazaspiro[4.5]decanone series.7–14
For example, addition of the (S)-methyl moiety as in (S)-16a increased
PLD1 activity ∼9-fold over (S)-14a, providing an ∼10-fold PLD1-
prefering inhibitor. With the analogous (R)-16a, activity was increased
at PLD1, but with a significant loss of inhibitory activity at PLD2. This
enantiospecific modulation of PLD activity was also conserved within
the entire series, with the (S)-methyl group engendering enhanced
PLD1 inhibition with a concomitant loss of PLD2 activity. Notable ex-
amples include (S)-16b, a potent dual PLD1 and PLD2 inhibitor (IC50s
of 1 nM and 12 nM, respectively) and (S)-14b, a 25-fold PLD2 pre-
ferring inhibitor, which converts to a dual PLD1/PLD2 inhibitor (S)-16d
upon incorporation of the (S)-methyl group. These data proved very
exciting, confirming that a single chemotype can provide PLD1-pre-
ferring, PLD2-preferring and dual PLD1/PLD2 inhibitors (Fig. 3) based
solely on the inclusion of either one or two easily established and
constructed chiral centers. These data also supported the first, and only
to date, issued U.S. composition of matter patent for PLD inhibitors.23
We next evaluated if these novel PLD inhibitors offer advantages in
terms of disposition relative to the earlier generation 2–6, which are
plagued by high plasma protein binding (rat and human fu < 0.03),
high predicted hepatic clearance (rat CLhep > 65 mL/min/kg) and very
short half-lives in vivo (t1/2 < 0.15 h). As shown in Table 2, analogs 14
human plasma, fus > 0.10) and (S)-14b and (S)-14d displayed im-
proved predicted hepatic clearance in rat (41.2 and 47.2 mL/min/kg,
respectively) and human (10.7 and 10.1 mL/min/kg, respectively).
3