Prepd from biotin by hydrogenolysis of the sulfide linkage: du Vigneaud et al., J. Biol. Chem. 146, 475 (1942). Improved prepn procedure: Melville et al., Science 98, 497 (1943). Synthesis: Melville, J. Am. Chem. Soc. 66, 1422 (1944); Wood, du Vigneaud, ibid. 67, 210 (1945); Duschinsky, Dolan, ibid. 2079; Bourquin et al., Helv. Chim. Acta 28, 528 (1954).