Arthogalin, a Cyclic Depsipeptide from the Lichen Arthothelium galapagoense

Arthogalin is a neutral compound of the m.p. 285-286 °C and gives no reaction with KOH, NaOCl, KOH + NaOCl, FeCl3 or /?-phenylenediamine. The high resolution MS yielded the for­ mula C24H 34N20 6 (found 446.225, ealed 446.242) and the NMR spectrum showed that arthogalin is a cyclic depsipeptide composed of one molecule of phenylalanine, one molecule of valine and two molecules of a-hydroxyisovaleric acid (1 ). ID and 2D NMR methods including inverse technique were used to determine the constitution of artho­ galin. The p ro ton-pro ton network and the pro­ ton -carbon assignment via lJ (C,H) were analysed by H, H-COSY and HM QC technique and in this way the following subunits could be identified: a-hydroxyisovaleric acid, phenylalanine, and va­ line. The chemical shifts of two of the subunits were very similar to the shifts of the amino acids phenylalanine and valine. Table I contains the ’Hchemical shifts and Table II the 13C-chemical shifts of arthogalin.