A facile approach to diosgenin and furostan type saponins bearing a 3beta-chacotriose moiety.
Combination of a one-pot coupling technique and the use of benzyl ethers as permanent protecting groups offered a short and simple route to dioscin-type saponins. This strategy in combination with a mild reductive opening procedure of the spiroketal function in diosgenin also offered a convenient approach to bidesmosidic furostan type saponins. Me(3)N.BH(3)/AlCl(3) promoted acetal opening of 3-O-TBDMS-protected diosgenin gave the 26-OH acceptor 9 into which a benzylated beta-glucose moiety was introduced by a S(N)2-type imidate coupling. After cleavage of the silyl ether, the 3beta-O-glucose and the 4-O-linked rhamnose of the chacotriose unit were introduced by a NIS/AgOTf-promoted one-pot coupling sequence utilising thioglycoside donors and their different reactivity in different solvents. After removal of a benzoyl group, the same coupling conditions were also used for the coupling of the second 2-O-linked rhamnose unit. The target substance was obtained after cleavage of the protecting benzyl ethers under Birch-type conditions, which did not affect the double bond in the steroid skeleton.
Lahmann
Martina
M
Department of Organic Chemistry, Stockholm University, S-10691 Stockholm, Sweden.
Gybäck
Helena
H
Garegg
Per J
PJ
Oscarson
Stefan
S
Suhr
René
R
Thiem
Joachim
J
D000970:Antineoplastic Agents / Q000138:chemical synthesis; D004144:Diosgenin / Q000031:analogs & derivatives*; D009682:Magnetic Resonance Spectroscopy; D012503:Saponins / Q000138:chemical synthesis*; D014326:Tropanes
D000970:Antineoplastic Agents; D012503:Saponins; D014326:Tropanes; C433845:chacotriose; C019357:dioscin; D004144:Diosgenin