| Abstract
| - Toralactone 9-O-β-d-glucopyranosyl-(1→6)-β-d-glucopyranosyl-(1→3)-β-d-glucopyranosyl-(1→6)-β-d-glucopyranoside (1, cassiaside C2), isolated from Cassiaobtusifolia L. and showing strongantiallergic activity, was concisely synthesized employing glycosyl trifluoroacetimidates as glycosylation agents. The unique naphtho-α-pyrone structure of toralactone (5) was constructed bycondensation of orsellinate 8 with pyrone 9 in the presence of LDA as developed by Staunton andco-workers. The naphthol of toralactone showed minimal reactivity as an acceptor and was screenedwith various glycosyl donors. It is finally concluded that sacrifice of an excess amount of thetrifluoroacetimidate or trichloroacetimidate donors (6f/6g, 6.0 equiv) in the presence of a catalyticamount of TMSOTf (0.05 and 0.3 equiv, respectively) afforded excellent yields of the couplingproduct, which was otherwise only a minor product under a variety of conditions examined.
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