Isoln from Rhodospirillum rubrum: Gloves, Threlfall, Biochem. J. 85, 14P (1962). Structure and synthesis: Moore, Folkers, J. Am. Chem. Soc. 87, 1409 (1965); 88, 567 (1966); Daves et al., ibid. 90, 5587 (1968).