Constituent of normal human urine: Koschara, Z. Physiol. Chem. 277, 284 (1943). Structure: Tschesche et al., Ber. 88, 1251 (1955). Revised structure: Goto et al., Tetrahedron Lett. 1967, 4507; eidem, J. Biochem. (Tokyo) 65, 611 (1969). Synthesis: Sakurai, Goto, Tetrahedron Lett. 1968, 2941; eidem, J. Biochem. (Tokyo) 65, 755 (1969).