11,9 was obtained from 9 by reflux with 4-nitrobenzylthiol,
10,10 and sodium methoxide followed by cleavage of the
isopropylidene group by trifluoroacetic acid in wet methanol
at 60 °C.
Previous syntheses of (N)-methanocarba nucleosides that
rely on compound 6 as a starting material have suffered from
the lengthy and low-yielding routes to this key intermedi-
ate.11,12 In particular, the route of Johnson and co-workers11a
to intermediate 6 required a cyclopentenone
intermediate obtained in low yield and featured a stannyl
intermediate for introducing the 5′-carbon. The route of
Marquez and co-workers11b was dependent on a low yield
cyclization of a diketophosphonate intermediate, which was
complicated by racemization. By our method, it was possible
to obtain 1 g of 6 starting from 5 g of D-(+)-ribono γ-lactone
(10.8% overall yield).
The newly synthesized (N)-methanocarba-NBTI deriva-
tive, 11, was examined for its ability to inhibit nucleoside
transport by the equilibrative transporters (es, ei)13 by
measuring initial rates of uptake of 10 µM 3H-uridine in the
presence or absence of graded concentrations of either 11
or NBTI (S-(4-nitrobenzyl)thioinosine)5 by cultured human
cells that possess only es (CCRF-CEM)14,15 or both es and
ei (HeLa)16 transporters. The IC50 values (concentrations that
inhibited transport rates by 50%) calculated from concentra-
tion-effect relationships for inhibition of es-mediated uridine
transport in CCRF-CEM cells by 11 and NBTI were,
respectively, 30-50 and 1-5 nM. Compound 11, like NBTI,
had no effect on ei-mediated transport of uridine by HeLa
cells at concentrations e1.0 µM.
Thus, the introduction of a conformationally constrained
ribose equivalent satisfied the conformational requirements
of the transport-inhibitory site. Compound 11 bound with
high affinity, only slightly less than that of NBTI, thereby
demonstrating that it, like NBTI, is a useful probe for analysis
of the es transporter. Further work will be required to
determine if other properties of the (N)-methanocarba
analogue give it advantages over NBTI as a potential
modulator of transport. Compound 11 also bound to the
human A3AR3 with a Ki of 1.97 ( 0.10 µM.
In summary, we developed an efficient synthetic meth-
odology for the cyclopentenone derivative 6, utilizing RCM
reaction as a key step, leading to a variety of carbocyclic
compounds. During the writing of this paper, Al-Abed and
co-workers17 reported the synthesis of carba-D-arabinose
using a similar strategy, including olefin metathesis, starting
from a carbohydrate source. In that study, the more reactive
and air-sensitive Schrock’s catalyst was used.
Acknowledgment. We thank Dr. Y. Choi, Dr. X.-D. Ji,
and Dr. V. E. Marquez for helpful discussions.
(8) Jeong, L. S.; Marquez, V. E.; Yuan, C.-S.; Borchardt, R. T.
Heterocycles 1995, 41, 2651.
(9) 1H NMR δ (CD3OD): 8.79 (s, 1H), 8.74 (s, 1H), 8.78, 8.15 (2s,
2H), 7.76, 7.64 (2s, 2H), 4.46-4.99 (m, 3H), 4.87 (s, 1H), 4.72 (s, 2H),
4.24 (m, 1H), 3.89 (m, 1H), 1.56 (m, 1H), 0.93 (m, 1H). HRMS (FAB):
calcd 430.1185, found 430.1171.
Supporting Information Available: Experimental pro-
cedures and spectroscopic data for compounds 2-3, 5, 6, 8,
9, and 11. This material is available free of charge via the
(10) Bellas, M.; Tuleen, D. L.; Field, L. J. Org. Chem. 1967, 32, 2590.
(11) (a) Medich, J. R.; Kunnen, K. B.; Johnson, C. R. Tetrahedron Lett.
1987, 28, 4131. (b) Marquez, V. E.; Lim, M.-I.; Tseng, C. K.-H.; Markovac,
A.; Priest, M. A.; Khan, M. S.; Kaskar, B. J. Org. Chem. 1988, 53, 5709.
(12) (a) Altman, K.-H.; Kesselring, R.; Francotte, E.; Rihs, G. Tetrahe-
dron Lett. 1994, 35, 2331. (b) Siddiqui, M. A.; Ford, H., Jr.; George, C.;
Marquez, V. E. Nucleosides Nucleotides 1996, 15, 235.
(13) “es” refers to equilibrative inhibitor-sensitive and “ei” refers to
equilibrative inhibitor-insensitive systems.
(14) Cass, C. E.; King, K. M.; Montano, J. T.; Janowska-Wieczorek, A.
Cancer Res. 1992, 52, 5879.
OL006999C
(15) Crawford, C. R.; Ng, C. Y.; Ullman, B.; Belt, J. A. Biochim. Biophys.
Acta 1990, 1024, 289.
(16) Boumah, C. E.; Hogue, D. L.; Cass, C. E. Biochem. J. 1992, 288,
987.
(17) Seepersaud, M.; Al-Abed Y. Tetrahedron Lett. 2000, 41, 7801.
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