Monoterpene biosynthesis. I. Occurrence and mevalonoid origin of gentiopicroside and loganic acid in Swertia caroliniensis

Abstract

Gentiopicroside (l), a secoiridoid monoterpene glucoside, and loganic acid (2), a new naturally occurring iridoid monoterpene glucoside, have been isolated from the same higher plant, Swertia caroliniensis. These congeners have been characterized by chemical and spectral means. Doubleresonance nuclear magnetic resonance studies corroborated a recently revised structure 1 for gentiopicroside, isomeric to the previously designated one l a . Loganic acid has been identified by methylation to loganin (3), and acetylation to pentaacetate derivatives. Tracer experiments with acetate-2-14C, mevalonate-2-14C (6), and me~alonate-2-~H have established the mevalonoid origin of the aglucone moieties of the glucosides. Conversion of mevalonate-labeled gentiopicroside into genti-G entiopicroside (1) and loganic acid (2) belong to a class of highly oxygenated monoterpene glucosides referred to as secoiridoids and iridoids, respectively. (For a review of the iridoids (cyclopentanoid monoterpenes), see Bobbitt and Sege-

The iridoid glucoside secologanin is derived from the novel triose phosphate/pyruvate pathway in a Catharanthus roseus cell culture

“…Nowadays it is accepted that the pathway passes through 10‐hydroxygeraniol, 10‐oxogeranial, iridodial, iridotrial, loganic acid and loganin [9]. In this pathway, substantial data from tracer experiments for the intermediacy of mevalonate were obtained, although with low incorporation rates [10–12]. However, it was recently shown that in some essential oils, geraniol was not of mevalonoid origin but derived from 1‐deoxy‐ d ‐xylulose [13].…”

Chemotaxonomic Studies of Nine Gentianaceae Species from Western China Based on Liquid Chromatography Tandem Mass Spectrometry and Fourier Transform Infrared Spectroscopy

“…Although several xanthones were isolated from Gentiana species such as G. lutea, a traditional European food and medicine, iridoid glycosides were also the major components with notably high contents present in this species (Mustafa et al, 2014). According to previous studies, the biosynthesis of iridoid glycosides complies with traditional mevalonic acid (MVA) pathway ( Jensen and Schripsema, 2002) and 1-deoxy-D-xylulose 5-phosphate (DXP) pathway (Coscia et al, 2002;Lichtenthaler, 1999) in Gentianaceae species. Several possible biosynthetic branches of identified iridoid glycosides in this study are drawn in Fig.…”

Enzymic synthesis of loganin by carboxyl group methylation of loganic acid

“…Tender leaves and shoots from 4-8 month old V. rosecl plants were used for the preparation of cellfree extracts. Loganic acid was isolated from Swertia curoliniensis and purified as previously described [6] .…”