Prepn of dl-form: Harington, McCartney, Biochem. J. 21, 852 (1927); Borrows et al., J. Chem. Soc. 1949, Suppl. Issue No. 1, S199, S204; Siedel et al., US 2894977 (1959 to Hoechst). Prepn of l(+)-form: Harington, Biochem. J. 22, 1429 (1928); Chambers et al., J. Chem. Soc. 1949, 3424; Hillmann, US 2886592 (1959); as the hydrochloride: Anthony, US 2950315 (1960 to Baxter); Meltzer, US 3102136 (1963 to Warner-Lambert). Prepn of d(-)-form: Harington, loc. cit.; Elks, Waller, J. Chem. Soc. 1952, 2366.