PNNL

Abstract

A series of Wrightia hanleyi extracts was screened for activity against M. tuberculosis. One active fraction contained a compound that appeared to be either the isoflavonoid wrightiadione or the alkaloid tryptanthrin, both of which have been previously reported in other Wrightia species. Characterization by NMR and high resolution MS as well as evaluation of the literature describing these compounds suggests wrightiadione was misidentified in the first report of its isolation from W. tomentosa 1992 and again in 2015 when reported in W. pubescens and W. religiosa. Instead, the molecule described in these reports and in the present work is almost certainly the isobaric (same nominal mass) and isosteric (same number of atoms, valency, and shape) tryptanthrin, a well-known alkaloid found in a variety of plants including Wrightia species. Tryptanthrin is also accessible synthetically via several routes, and has been thoroughly characterized. True wrightiadione has been synthesized and characterized and may have useful biological activity; however this compound can no longer be said to be known to exist in nature. To our knowledge, this misidentification of wrightiadione has heretofore been unrecognized.