title: A facile approach to diosgenin and furostan type saponins bearing a 3beta-chacotriose moiety.
abstract: 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.
authors.affiliation: Department of Organic Chemistry, Stockholm University, S-10691 Stockholm, Sweden.
authors.forename: Martina
authors.initials: M
authors.lastname: Lahmann
authors.forename: Helena
authors.initials: H
authors.lastname: Gybäck
authors.forename: Per J
authors.initials: PJ
authors.lastname: Garegg
authors.forename: Stefan
authors.initials: S
authors.lastname: Oscarson
authors.forename: René
authors.initials: R
authors.lastname: Suhr
authors.forename: Joachim
authors.initials: J
authors.lastname: Thiem
mesh_terms: D000970:Antineoplastic Agents / Q000138:chemical synthesis; D004144:Diosgenin / Q000031:analogs & derivatives*; D009682:Magnetic Resonance Spectroscopy; D012503:Saponins / Q000138:chemical synthesis*; D014326:Tropanes
chemical_list: D000970:Antineoplastic Agents; D012503:Saponins; D014326:Tropanes; C433845:chacotriose; C019357:dioscin; D004144:Diosgenin