1. Important reviews of naturally occurring pteridines have been prepared byR. C. Elderfield andA. C. Metha inHeterocyclic Compounds (Ed.R. C. Elderfield; John Wiley and Sons, Inc., New York, N.Y. 1967), Vol. 9, p. 1–117 — andW. Pfleiderer, Angew. Chem. (Int. Ed. Engl.),3, 114 (1964).
2. G. R. Pettit, J. L. Hartwell andH. B. Wood, Cancer Res.28, 2168 (1968).
3. R. Purrmann, Justus Liebigs Annln Chem.544, 182 (1940);546, 98 (1940) and548, 284 (1941).
4. The active constituents ofPrioneris thestylis are being examined in our laboratory and represent a new series of butterfly components.