No abstract

During investigations on the hydrolysis of a protopanaxatriol-type saponin mixture by various glycoside hydrolases, it was found that two minor saponins, ginsenosides Rg 2 and Rh 1, were formed in high yields by crude beta-galactosidase from Aspergillus oryzae and crude lactase from Penicillium sp., respectively. Moreover, a crude preparation of naringinase from Penicillium decumbens readily hydrolyzed a protopanaxatriol-type saponin mixture to give an intestinal bacterial metabolite, ginsenoside F 1 as the main product. A crude preparation of hesperidinase from Penicillium sp. selectively hydrolyzed ginsenoside Re into ginsenoside Rg 1. This is the first report on the enzymatic preparation of minor saponins, ginsenosides Rg 2 and Rh 1, and of an intestinal bacterial metabolite, ginsenoside F 1, with a high efficiency from a protopanaxatriol-type saponin mixture.

[reaction: see text] The chiral palladium complex generated in situ from [Pd(eta(3)-allyl)Cl](2) and (R)-BINAP is a good catalyst for the catalytic asymmetric allylation of 1,3-diketones. The reaction provided chiral 2,2-dialkyl-1,3-diketones with 64-89% ee in high yields (13 examples). Enantiomeric excesses are strongly affected by the gamma-substituent of the allylic substrates. A variety of unsymmetrical 1,3-diketones were alkylated with cinnamyl acetate in good enantioselectivities via use of the BINAP-palladium catalyst (77-89% ee).

We have already exploited several convenient methods2 for introducing nucleophiles (R-) to the position a to the nitrogen atom of carbamates 1 using anodically prepared a-methoxylated carbamates 2 as the key intermediates (eq 11.3 1 2 Although this method is applicable to syntheses of a variety of alkaloid^?^ enantioselective introduction of Rat the a position remains to be investigated. Our methodology for this purpose is shown in Scheme I in which (1) chiral compounds 3 are anodically prepared from a-amino acids (step a), (2) R-is diastereoselectively introduced to the a-position through the influence of a substituent on the chiral a'-position (step b), (3) the a'-substituent is eliminated after R-is introduced (step c), and (4) formally enantioselective introduction of R-to the a-position is thus attained through these steps.Although we have already described this methodology in a preliminary note: recent publication of a report6 on the synthesis of optically active alkaloids using our methodology prompted us to report our new findings.Optically active (+)-N-methylconiine 10 was synthesized according to the route outlined in Scheme 11.The key intermediate 5 was prepared by anodic oxidation of 4 derived from L-lysine followed by treatment with acid.5 Treatment of 5 with allyltrimethylsilane followed by hydrogenation gave the cis isomer 6 exclusively. Hydrolysis of 6 followed by anodic decarboxylation7 gave 8, which was then successively reduced with NaBH, and (1) Electroorganic Chemistry, 96.(2) (a) Shono, T.; Mataumura, Y.; Tsubata, K. (3) Shono, T.; Hamaguchi, H.; Matsumwa, Y. J. Am. Chem. SOC. 1975, 97, 4264. (4) Shono, T.; Matsumura, Y.; Uchida, K.; Tsubata, K.; Makino, A. J. Org. Chem. 1984,49, 300. (5) (a) Whole process of this methodology has been presented at the 3rd Synoposium on Electroorganic Chemistry, Osaka, Japan (19829, Abstr. p 59. (b) Shono, T.; Matsumura, Y.; Inoue, K. J. Chem. SOC., Chem. Commun. 1983,1169. (c) Shono, T.; Matsumura, Y.; Tsubata, K.; Sugihara, Y.; Yamane, S.; Kanazawa, T.; Aoki, T. J. Am. Chem. SOC. 1982, 104,6697. (6) Irie, K.; Aoe, K.; Tanaka, T.; Saito, S. J. Chem. SOC., Chem. Commun. 1985,633. (7) Iwasaki, T.; Horikawa, H.; Matsumoto, K.; Miyoshi, M. J. Org. Chem. 1979,44, 1552.