Studies Towards the Synthesis of the β‐D‐Xyl‐(1 → 3)‐L‐ara Disaccharide Moiety of OSW‐1 from Ornithogalum saundersiae
摘要:
The OSW-1 disaccharide having 2-O-p-methoxybenzoyl-beta-D-xylopyranosyl-(1 --> 3)-L-arabinopyranoside structure was obtained as the benzylated 4-O-acetyl derivative 19. Also, the 4,2'-di-O-acetate 18 was synthesized by a short synthetic approach. The arabinose acceptor 15 was obtained in a three step-one pot sequence from easily available benzyl beta-L-arabinopyranoside.
Dioxolane type 3,4-benzylidene acetals of benzyl beta-l-arabinose either as a mixture or pure exo- and endo-isomers cleavaged with BF(3).OEt(2)/Et(3)SiH in dichloromethane or acetonitrile regioselectively, provided the 4-O-benzyl-3-hydroxy derivative. The reaction with TiCl(4)/Et(3)SiH or Cu(OTf)(2)/Et(3)SiH provided a mixture of 3- and 4-O-benzyl derivatives whereas with Cu(OTf)(2)/BH(3).THF gave