THE BIOSYNTHESIS OF TROPIC ACID - THE STEREOCHEMICAL COURSE OF THE MUTASE INVOLVED IN HYOSCYAMINE BIOSYNTHESIS IN DATURA-STRAMONIUM

Incubation of (R,S)-DL-phenyl[2-H-3]lactic acid with Datura stramonium generates hyoscyamine 2 with the tritium isotope located at C-3' of the tropic acid ester moiety; the C-3' hydroxymethyl group of 2 is converted into a chiral methyl group and is oxidised to generate chiral sodium acetate, with the (R) configuration (96% ee); the tritium is therefore located at the 3'-pro-S site of 2; it follows that the 3'-pro-R hydrogen is introduced with inversion of configuration by the mutase operating during hyoscyamine biosynthesis.