To improve the oral bioavailability of a dermorphin tetrapeptide analog, N(alpha)-1-iminoethyl-Tyr-D-MetO-Phe-MebetaAla-OH (III), which has a potent analgesic activity after oral administration, various derivatives were synthesized to increase lipophilicity by esterification of the C-terminal carboxyl group and/or acylation of the phenolic hydroxyl group on Tyr1. Antinociceptive activity was evaluated after subcutaneous or oral administration using the mouse tail pressure test. As a result, increased antinociceptive activity after oral administration as well as an improved ED50(p.o.)/ED50(s.c.) ratio, which is an indicator of oral bioavailability, were found for some compounds. With regard to the improvement of bioavailability, derivatives with acylation of the phenolic hydroxyl group on Tyr1 showed better results than derivatives with esterification of the C-terminal carboxyl group. In particular, an ED50(p.o.)/ED50(s.c.) ratio equivalent to that of morphine was found for an acetylated derivative, N(alpha)-1-iminoethyl-Tyr(COMe)-D-MetO-Phe-MebetaAla-OH (7a), as well as for a methoxycarbonylated derivative, N(alpha)-1-iminoethyl-Tyr(CO2Me)-D-MetO-Phe-MebetaAla-OH (7l).

Both enantiomers of C2-symmetric dimethyl 3,7-dihydroxybicyclo[3.3.0]-octa-2,6-diene-2,6-dicarboxylate 3 were prepared in enantiomerically pure form from symmetric tetraester 1 by the lipase-catalyzed demethoxycarbonylation, respectively. Double asymmetric differentiation with lipase in the above demethoxycarbonylation was observed. Their applications to formal total syntheses of (+)-carbacyclin and (−)-ajmalicine including (−)-tetrahydroalstonine are also described.

sigma-Symmetric bicyclic diketones 8a-c were enantioselectively reduced with baker's yeast to give the chiral hydroxy ketones 7a-c in 74-100% ee. The reduction product (+)-7a and (-)-7'c were shown to be the chiral intermediates for the total synthesis of cantabrenonic acids derivatives 3 and hirsutene (4), respectively. The subsequent transformation of (+)-7a gave the intermediate (+)-5 for the total synthesis of capnellenols (1, 2).