Prepn from broccoli-leaf extract: Wall, US 2555583 (1951 to U.S.D.A.). Review: H. Fischer, A. Stern, Die Chemie des Pyrrols vol. II, 2 (Leipzig, 1940) pp 91-94; The Chlorophylls, L. P. Vernon, G. R. Seely, Eds. (Academic Press, New York, 1966) pp 9, 12, 71, 90, 95, 98, 142.