Studies on Bignoniaceae: Newbouldiosides D - F, Minor Phenylethanoid Glycosides from Newbouldia laevis, and New Flavonoids from Markhamia zanzibarica and Spathodea campanulata

Abstract

Continued examination of the stem bark of Newbouldia laevis afforded three minor phenylethanoid glycosides, designated as newbouldiosides D - F. Their structures were elucidated by spectroscopic methods as β-(3,4-dihydroxyphenyl)ethyl 5-O-syringoyl-β-D-apiofuranosyloxy-(1 → 2)-O-[α-L-rhamnopyranosyl-(1 → 3)]-6-O-E-sinapoyl-β-D-glucopyranoside, β-(3,4-dihydroxyphenyl)ethyl β-D-apiofuranosyloxy-(1 → 2)-O-[α-L-rhamnopyranosyl-(1 → 3)]-6-O-E-sinapoyl-β-D-glucopyranoside, and β-(3,4-dihydroxyphenyl)ethyl β-D-apiofuranosyloxy-(1 → 2)-O-α-L-rhamnopyranosyl-(1 → 2)-6-O-E-sinapoyl-β-D-glucopyranoside, respectively. These metabolites are the first members possessing a sinapoyl structural element. In addition, the series of naturally occurring flavonoids is extended by the identification of 3',4',5,7-tetrahydroxy-5'-methoxyflavanone and apigenin-5-O-α-L-rhamnopyranosyl-7-O-β-D-glucopyranoside obtained from leaf extracts of Markhamia zanzibarica and aromadendrin-7-O-(2″-O-formyl)-β-D-glucopyranoside isolated from Spathodea campanulata. The latter compound is the first example of a flavonoid possessing a formylated glucosyl moiety.