Indole and flavanoid constituents of Wrightia tinctoria, W. tomentosa and W. coccinea

Abstract

Members of the genus <i>Wrightia, </i>viz. <i>W. tinctoria, W. tomentosa </i>and <i>W. coccinea, </i>have been investigated for their chemical constituents with a view to locating their bioactive principles. Indigotin <b>3</b>, indirubin <b>6</b>, tryptanthrin <b>8</b>, isatin <b>5</b>, anthranillate <b>7</b> and rutin <b>9</b> have been isolated and identified as major constituents of <i>W. tinctoria </i>and <i>W.tomentosa. </i>Anthranillate

<b>7</b> and rutin <b>9</b> are the major constituents of <i>W. coccinea. </i>The identities of these compounds have been established by comprehensive chromatographic (HPTLC, HPLC) and spectroscopic (UV-VIS, IR, EI-MS) techniques, using markers and by synthesis, where possible. While indigotin is found to be native in the living plants (in fresh leaves), indirubin was found to be an artifact formed only during drying process after harvesting of the leaves. This transformation is presumably caused by the intact hydrolytic enzyme system(s) and by autoxidation. Seasonal variation studies of the chemical constituents of leaves, using HPTLC and HPLC analyses, revealed similar variation patterns in the three species. The concentration of indigotin-indirubin combination steadily increases from August to November. In contrast, concentration of isatin and anthranillate increases in the months of December and January, at the expense of indigotin-indirubin. !satin is produced by the

autoxidation of indigotin. Tryptanthrin concentration also increases, periodically, in May (at the expense of isatin) and in January. Plausible pathways for the formation of these indole metabolites are appraised on the basis of circumstantial and synthetic evidence.