2460
T. A. Rano et al. / Bioorg. Med. Chem. Lett. 19 (2009) 2456–2460
Table 6
%F = Dose(IV) AUC(PO)/ Dose(PO) AUC(IV)
*
*
Compound
Species (n = 4)
Cmax (ng/mL)
Tmax (h)
T1/2 (h)
AUC (ngÁh/mL)
%F
Clp (mL/min/kg)
Vss (L/kg)
Tetrahydroquinoline A (p.o.)
Tetrahydroquinoline A (i.v.)
Rat (10 mpk)
Rat (2 mpk)
950
31,400
6
—
28
17.4
31,300
18,900
31
—
—
1.8
—
0.36
establishes the fact that almost all attempts to improve the po-
tency of compound 52 fell short of the mark, except for compound
62 (IC50 = 125 nM), which differed from compound 52 only by the
replacement of the trifluoromethyl with a methyl group. Again,
several analogs of these compounds were prepared, but none were
as potent as compound 19. Since compound 19 proved to be very
potent in our binding assay, even as a racemic mixture, we decided
to resolve a small amount of the penultimate intermediate of 19
(unalkylated aniline, not shown) via chiral HPLC, followed by alkyl-
ation with 1,1,1-trifluoroepoxypropane. Separation of the resultant
diastereomers by SiO2 chromatography afforded enantiomerically
pure Tetrahydroquinoline A (once again, the ‘higher Rf’ compound).
Concomitantly, an asymmetric synthesis of compound 19 was
also established in order to determine the absolute stereochemical
configuration of the chiral centers.15 These results, which are illus-
trated in Table 5, determined that the R,S stereochemical configu-
ration (Tetrahydroquinoline A) possessed the best potency of the 4
possible diastereomers, displaying an IC50 = 39 nM. This compound
was selected for further study.
The pharmacokinetic profile of Tetrahydroquinoline A was
determined in Sprague–Dawley rats dosed at 10 mg/kg, using ses-
ame oil as the vehicle for the po route. For the iv arm dosed at
2 mg/kg, values of plasma clearance (Clp) volume of distribution,
(Vss) and plasma half-life (T1/2) were calculated using Tetrahydro-
quinoline A formulated in 10% EtOH:10% solutol:80% D5W. Mean
pharmacokinetic parameters of Tetrahydroquinoline A (illustrated
in Table 6) indicate the average oral bioavailability to be 31%.
P-450-mediated metabolism is not a major elimination pathway.
Overall, Tetrahydroquinoline A demonstrates favorable ADME
characteristics.16 Further studies on Tetrahydroquinoline A are
ongoing and will be reported in due course.
References and notes
1. Tall, A. R. J. Lipid Res. 1993, 34, 1255.
2. McCarthy, P. A. Med. Res. Revs. 1993, 13, 139.
3. For an excellent review of CETP inhibitors, see: Sikorski, J. A. J. Med. Chem. 2006,
49, 1.
4. (a) Harikrishnan, L. S.; Kamau, M. G.; Herpin, T. F.; Morton, G. C.; Liu, Y.; Cooper,
C. B.; Salvati, M. E.; Qiao, J. X.; Wang, T. C.; Adam, L. P.; Taylor, D. S.; Chen, A. Y.
A.; Yin, X.; Seethala, R.; Peterson, T. L.; Nirschl, D. S.; Miller, A. V.; Weigelt, C. A.;
Appiah, K. K.; O’Connell, J. C.; Lawrence, R. M. Bioorg. Med. Chem. Lett. 2008, 18,
2640; (b) Eary, C. T.; Jones, Z. S.; Groneberg, R. D.; Burgess, L. E.; Mareska, D. A.;
Drew, M. D.; Blake, J. F.; Laird, E. R.; Balachari, D.; O’Sullivan, M.; Allen, A.;
Marsh, V. Bioorg. Med. Chem. Lett. 2007, 17, 2608; (c) Bruckner, D.; Hafner, F. T.;
Li, V.; Schmeck, C.; Telser, J.; Vakalopoulos, A.; Wirtz, G. Bioorg. Med. Chem. Lett.
2005, 15, 3611.
5. Barter, P. J.; Caulfield, M.; Eriksson, M.; Grundy, S. M.; Kastelein, J. J. P.;
Komajda, M.; Lopez-Sendon, J.; Mosca, L.; Tardif, J. C.; Walters, D. D.; Shear, C.
L.; Revkin, J. H.; Buhr, K.; Fisher, M. R.; Tall, A. R.; Brewer, B. N. Eng. J. Med. 2007,
357, 2109.
6. Shinkai, H.; Maida, K.; Yamasaki, T.; Okamoto, H.; Uchida, I. J. Med. Chem. 2000,
43, 3566.
7. Reinhard, E. J.; Wang, J. L.; Durley, R. C.; Fobian, Y. M.; Grapperhaus, M. L.;
Hickory, B. S.; Massa, M. A.; Norton, M. B.; Promo, M. A.; Tollefson, M. B.;
Vernier, W. F.; Connolly, D. T.; Witherbee, B. J.; Melton, M. A.; Regina, K. J.;
Smith, M. E.; Sikorski, J. A. J. Med. Chem. 2003, 46, 2152.
8. The sodium salt of dimethyl malonate or di-tertbutyl malonate could also be
used with equal efficiency. In the latter case, the mono carboxylic acid could be
obtained via the two step process of tertbutyl esters removal with TFA,
followed by 6 N HCl heated to reflux.
9. Markgraf, J. H.; Ibsen, M. S.; Kinney, J. B.; Kuper, J. W.; Lurie, J. B.;
Marrs, D. R.; McCarthy, C. A.; Pile, J. M.; Pritchard, T. J. J. Org. Chem.
1977, 42, 2631.
10. Stannane 3 was prepared from the corresponding commercially available aryl
bromide under standard condition employing Me3SnSnMe3 and Pd(PPh3)4 in
approximately 65% yield.
11. Salunkhe, A. M.; Brown, H. C. Tetrahedron Lett. 1995, 36, 7987. Interestingly,
several other commonly employed methods of azide reduction resulted in
intractable mixtures, the exception being PPh3/H2 O, which afforded the
desired amine in 28% yield.
Tetrahydroquinoline
A
exhibited
a
high permeability
(4.7 Â 10À6 cm/s) in Caco2 cells. The metabolic stability of Tetrahy-
droquinoline A in human, rat, monkey, mouse and dog liver micro-
somal preparations was also determined. The
t
½
of
Tetrahydroquinoline A in pooled microsomes from each species
was calculated and found to be acceptable, with the compound dem-
onstrating a t of >128 min in human liver microsomes. Tetrahydro-
½
quinoline A was also tested for inhibition of Cytochrome P450
isozymes CYP2C9, CYP2A6, CYP2C19, CYP2D6, CYP2E1, CYP1A2,
and CYP3A4 in human liver microsomes, and was shown to have
no significant inhibitory effect on most P450 isozymes tested.
In conclusion, we have demonstrated that the 1,2,3,4-tetrahy-
droquinoline moiety can provide a versatile platform for designing
a diverse array of potent CETP inhibitors, resulting in the prepara-
tion of the bi-phenyl analog Tetrahydroquinoline A. Although Tet-
12. Yamada, K.; Kubo, T.; Tokuyama, H.; Fukuyama, T. Synlett 2002, 2, 231.
13. Buck, E.; Song, Z. J.; Tschaen, D.; Dormer, P. G.; Volante, R. P.; Reider, P. J. Org.
Lett. 2002, 4, 1623.
14. The primary screen for determining CETP inhibitory utilizes a commercially
available kit sold by Amersham Biosciences. This kit is SPA based and contains
partially purified human plasma-derived CETP, [3H]-HDL-C, biotinylated LDL-C,
buffer and strepavidin SPA beads. The reagents (except SPA beads) are added to
96 well plates according to the manufacturer’s instructions and either vehicle
(DMSO, 1%) or compounds are added before an overnight incubation at 37 °C. A
stop reagent and the SPA beads are then added and incubated with the reaction
mixture for 30 min. The radioactivity is then counted and data are expressed as
the% inhibition relative to vehicle controls. IC50 values are generated using
GraphPad prism software.
15. The asymmetric preparation of Tetrahydroquinoline A has been submitted to
Org. Lett.
16. For a detailed report of the biological evaluation of Tetrahydroquinoline A,
please see: Kuo, G. H.; Rano, T.; Pelton, P.; Demarest, K. T.; Gibbs, A. C.; Murray,
W. V.; Damiano, B. P.; Connelly, M. A. J. Med. Chem. 2009, 56, 1768.
rahydroquinoline
A
is highly permeable (4.7 Â 10À6 cm/sec),
absorption was delayed (mean Tmax ꢀ 6 h) after oral administra-
tion in sesame oil. Following iv administration of Tetrahydroquin-
oline A to rats, clearance was about 3% of hepatic blood flow.
Elimination t was long (ꢀ28 h) and the compound showed little
½
distribution beyond the central compartment. Low clearance
values and a long t in microsomes suggest that cytochrome
½