Alternative methods for the production and modification of natural products.

Abstract

Alternative methods for the production of several triterpenoid compounds were investigated. The first compound, 15-glucopyranosylglaucarubolone, has been isolated from the desert plant Castela emoryi (Gray) Moran and Felger (Simaroubaceae) and has been found to have potent activity against grape downy mildew (Plasmopara viticola) (Hoffmann et al., 1992). During the course of this research, methods for the production of C. emoryi callus, suspension, root, and shoot cultures were developed. These cultures were analyzed via HPLC for the presence of 15-glucopyranosylglaucarubolone as well as two other closely related compounds, glaucarubolone and holacanthone. Biotransformation of holacanthone and glaucarubolone was also investigated as a means of producing 15-glucopyranosylglaucarubolone. Microbial transformation of holacanthone by five different microbes produced glaucarubolone but not the glucoside. Excised root cultures of Castela emoryi successfully converted glaucarubolone into the active metabolite 15-glucopyranosylglaucarubolone. The excised shoot culture, on the other hand, converted glaucarubolone into the acetylated compound, holacanthone. The second half of this investigation involved the feasibility of converting three triterpenoids (incanilin, argentatin A, and argentatin B) from the hybrid, Parthenium argentarum x Parthenium tomentosa, into biologically active compounds. These compounds, which are isolated in high yields from the hybrid, are structurally similar to two compounds that have biological activity. Deacetoxypapyrific acid, from the plant Betula glandulosa has been found to have rodent antifeedant activity (Williams et al., 1992). Polacandrin from the plant Polanisia dodecandra, has cytotoxic activity (Shi et al., 1992). Microbial 12β-hydroxylation was investigated as a first step towards generating the desired activities. Microbial transformation of incanilin acetate and argentatin A acetate by Septomyxa affinis and Gibberella saubinetii generated the 3-keto reduction metabolites, 20,24-epoxy-lanost-8-ene-3,25-diol-16-acetate and 20,24-epoxy-cycloart-3,25-diol-16-acetate. In addition, the S. affinis transformations also produced several interesting A-ring scission products: 20,24-epoxy-3,4-seco-lanost-8-ene-4,25-diol-16-acetyl-3-oic acid; 20,24-epoxy-3,4-seco-cycloart-4,25-diol-16-acetyl-3-oic acid; 20,24-epoxy-3,4- seco-lanost-1,8-diene-4,25-diol-16-acetyl-3-oic acid; 20,24-epoxy-3,4-seco-cycloart-1-ene-4,25-diol-16-acetyl-3-oic acid; and 20,24-epoxy-3,4-seco-lanost-1,4(28),8-triene-25-ol-16-acetyl-3-oic acid. In the process of isolating incanilin and argentatin A, a new, previously unreported triterpenoid, cycloart-25-ene-3-one-16,24-diol, was isolated and identified by spectral analysis as the 16-acetate, 16-acetoxy-cycloart-25-ene-3-one-24-ol.