Structure Determination of Tigridial, an Iridopentaene from Tigridia pavonia (Iridaceae)

Abstract

Besides numerous known iridals, which are unusual monoNaBH 4 . The products 15a,b and 16a,b of this reaction sequence were isolated and their structures elucidated by or bicyclic triterpenoids of Iridaceae, lipid extracts of Tigridia pavonia bulbs contain tigridial (17), a new spirobicyclic spectroscopic techniques. From these results structure 17 was inferred for the new natural product, which was confirmed hemiacetal with a conjugated pentaene moiety in the terpenoid side chain. The isolated natural product by 1D and 2D NMR spectroscopy of a mixture of 11 and 17, in which the latter had been stabilized by addition of decomposes rapidly despite exclusion of light and oxygen. In contrast, derivatives of 17 formed by Diels-Alder reaction hydroquinone. The stereochemistry of 17 was deduced from 2D NOE experiments and comparison with known with 4-phenyl-3H-1,2,4-triazole-3,5-(4H)-dione (13) are stable, as are the products of a subsequent reduction with compounds.