The biogenesis of alkaloids. XIII. The role of ornithine in the biosynthesis of stachydrine.

Stachydrine (I), the methyl betaine of proline, occurs in a number of plants (1). Its biogenesis has been the subject of an investigation by Klein and Linser (2) who found an increase in stachydrine content of the planbs after an injection of proline into the hollow stems of Guleopsis ochroleuca and Stachys palustris. They suggest two schemes for the biogenesis of proline, one from ornithine, the other from glutamic acid via pyrrolidonecarboxylic acid. The metabolic relationship of ornithine, proline, and glutamic acid has been studied in molds (3) and animals (4, 5). The most recent invest!igations of Stetten with animals (4) and of Fincham with molds (3) indicate that there are two likely pathways linking the three compounds. According to Stetten, the intermediate in the major pathway of proline biogenesis, i.e. glutamic semialdehyde, arises mainly by reduction of glutamic acid, and only to a small extent by 6 transamination of ornithine. The route from ornithine by ~1 transamination via Lu-keto-&aminovaleric acid is of minor importance in animals. In the higher plants, however, this last route is the only one which has been experimentally demonstrated (6), and our recent work showing that the biogenesis of the pyrrolidine ring present in the tropine part (III) of the alkaloid hyoscyamine proceeds from ornithine (7) strengthens this evidence. Stachydrine (I) may be regarded as the simplest of the pyrrolidine alkaloids, of which hygrine (II) and cuscohygrine are the most important members. These in turn may be related in structure to the tropane alkaloids with which they occur in I?rythroxylon Iruxillense Rushy, and, while some species of Convolvulzbs contain hygrine and cuscohygrine (C.