iridoids and tryptamine

Secologanin, a secoiridoid glucoside, is a pivotal terpenoid intermediate in the biosynthesis of biologically active monoterpenoid indole alkaloids such as reserpine, ajmaline, and vinblastine which are biosynthesized via strictosidine, an alkaloidal glucoside, formed from secologanin and tryptamine. In secologanin biosynthesis, the oxidative cleavage process of loganin to secologanin and the hydroxylation of 7-deoxyloganin to loganin have remained unknown enzymologically and mechanistically. Cornoside is a unique glucoside with 4-hydroxy-2,5-cyclohexadien-1-one (benzoquinol) ring and is widespread in families such as Cornaceae, Oleaceae, and Scrophulariaceae but its biosynthesis, especially the oxidative process, remain to be investigated. Shikonin is a red naphthazarin pigment derived from the roots of Lithospermum erythorhizon and produced biotechnologically by cell cultures. Its biosynthesis including the production regulation mechanism has been investigated in detail. However, the naphthazarin ring formation process, probably starting with the hydroxylation of the side chain of geranylhydroquinone, a key intermediate at the late stage of shikonin biosynthesis, remained unknown. In the present review, cytochrome P450 monooxygenases involved in the biosyntheses of three structurally and biosynthetically interesting compounds, secologanin, cornoside, and shikonin, a described together with the results of previous and recent biosynthetic studies. The biosyntheses of related compounds are also discussed.

Topics: Cyclohexanones; Cytochrome P-450 Enzyme System; Glucosides; Indole Alkaloids; Iridoid Glucosides; Iridoids; Naphthoquinones; Oxidation-Reduction; Plants; Secologanin Tryptamine Alkaloids; Tryptamines; Vinca Alkaloids

We report 14 harmala and tryptamine-iridoid alkaloids with various tri-, tetra- and pentacyclic cores from leaves and stem bark of six species of the large and complex neotropical genus Palicourea. Among them is the previously undescribed compound deoxostrictosamide which is related to strictosamide, a key intermediate in camptothecin biosynthesis. In addition, we describe the occurrence of 1,2,3,4-tetrahydronorharman-1-one for the first time within Rubiaceae and ophiorine A and B, two alkaloids with an unusual core bearing a betaine function and a zwitterion as new for the genus. Although the other compounds are already known from other species, their degree of structural diversity highlights the remarkable biosynthetic capabilities of the genus Palicourea. Furthermore, the present paper provides additional support for the hypothesis that tryptamine-iridoid alkaloids represent a distinct chemosystematic feature for the genus Palicourea.

Topics: Alkaloids; Biodiversity; Camptothecin; Costa Rica; Iridoids; Molecular Structure; Nuclear Magnetic Resonance, Biomolecular; Plant Extracts; Plant Leaves; Rubiaceae; Tryptamines; Vinca Alkaloids

The manipulation of pathways to make unnatural variants of natural compounds, a process often termed combinatorial biosynthesis, has been robustly successful in prokaryotic systems. The development of approaches to generate new-to-nature compounds from plant-based pathways is, in comparison, much less advanced. Success will depend on the specific chemistry of the pathway, as well as on the suitability of the plant system for transformation and genetic manipulation. As plant pathways are elucidated, and can be heterologously expressed in hosts that are more amenable to genetic manipulation, biosynthetic production of new-to-nature compounds from plant pathways will become more widespread. In this chapter, some of the key strategies that have been developed for metabolic engineering of plant pathways, namely directed biosynthesis, mutasynthesis, and pathway incorporation of engineered enzymes are highlighted. The iridoid-derived monoterpene indole alkaloids from C. roseus, which are the focus of this chapter, provide an excellent system for developing these strategies.

Topics: Biological Products; Biosynthetic Pathways; Carbon-Nitrogen Lyases; Catharanthus; Culture Media; Indole Alkaloids; Iridoid Glucosides; Iridoids; Metabolic Engineering; Monoterpenes; Mutagenesis, Site-Directed; Plant Proteins; Plasmids; Tryptamines; Vinca Alkaloids

Among the pharmacologically important terpenoid indole alkaloids produced by Catharanthus roseus are the anti-cancer drugs vinblastine and vincristine. These two drugs are produced in small yields within the plant, which makes them expensive to produce commercially. Metabolic engineering has focused on increasing flux through this pathway by various means such as elicitation, precursor feeding, and introduction of genes encoding specific metabolic enzymes into the plant. Recently in our lab, a feedback-resistant anthranilate synthase alpha subunit was over-expressed in C. roseus hairy roots under the control of a glucocorticoid inducible promoter system. Upon induction we observed a large increase in the indole precursors, tryptophan, and tryptamine. The current work explores the effects of over-expressing the anthranilate synthase alpha or alpha and beta subunits in combination with feeding with the terpenoid precursors 1-deoxy-D-xylulose, loganin, and secologanin. In feeding 1-deoxy-D-xylulose to the hairy root line expressing the anthranilate synthase alpha subunit, we observed an increase of 125% in hörhammericine levels in the induced samples, while loganin feeding increased catharanthine by 45% in the induced samples. Loganin feeding to the hairy root line expressing anthranilate synthase alpha and beta subunits increases catharanthine by 26%, ajmalicine by 84%, lochnericine by 119%, and tabersonine by 225% in the induced samples. These results suggest that the terpenoid precursors to the terpenoid indole alkaloids are important factors in terpenoid indole alkaloid production.

Topics: Anthranilate Synthase; Catharanthus; Indole Alkaloids; Iridoid Glucosides; Iridoids; Plant Roots; Tryptamines; Tryptophan; Xylulose

Jasmonates enhance the expression of various genes involved in terpenoid indole alkaloid (TIA) biosynthesis in Catharanthus roseus. We applied precursor feeding to our C. roseus suspensions to determine how methyl jasmonate (MJ) alters the precursor availability for TIA biosynthesis. C. roseus suspensions were induced with MJ (100 microM) on day 6 and fed loganin (0.30 mM), tryptamine (0.15 mM), loganin plus tryptamine, or geraniol (0.1-1.0 mM) on day 7. While MJ increased ajmalicine production by 3-fold, induced cultures were still limited by terpenoid precursors. However, both induced and non-induced cultures became tryptamine-limited with excess loganin. Geraniol feeding also increased ajmalicine production in non-induced cultures. But MJ appeared to increase geraniol availability in induced cultures, due presumably to the increased expression of Dxs with MJ addition.

Topics: Acetates; Acyclic Monoterpenes; Catharanthus; Cells, Cultured; Cyclopentanes; Iridoids; Oxylipins; Secologanin Tryptamine Alkaloids; Terpenes; Tryptamines

On the occasion of having won the Lajos Winkler Medal, at first the author confessed his intellectual relation to the famous scientist. Then he presented his results in the study on the three-dimensional molecular structure and chemotaxonomy of the more than 2500 alkaloids derived from secologanin and tryptamine, and isolated from three plant families, only. The multiple genetic and structural connections among the individual compounds were supported by current and common organic reaction mechanisms. The unified and well articulated picture obtained on detailed search in electronic data bases demonstrated the order of the parts in the whole. The final section of the lecture appreciated the interplay of multiplicity and unity in our culture and education as well.

Topics: Electronic Data Processing; Indole Alkaloids; Iridoid Glucosides; Iridoids; Models, Molecular; Plants; Tryptamines

From the dried roots of Neonauclea sessilifolia, two new chromone-secoiridoid glycosides, sessilifoside and 7"-O-beta-D-glucopyranosylsessilifoside, and three novel indole alkaloid glycosides, neonaucleosides A, B, and C, were isolated along with the main known glycosides, 5-hydroxy-2-methylchromone-7-O-beta-D-apiofuranosyl-(1-->6)-beta-D-glucopyranoside, sweroside, loganin, grandifloroside, and quinovic acid 3 beta-O-beta-D-quinovopyranoside-28-O-beta-D-glucopyranoside. The structures of these new glycosides were determined by spectroscopic and chemical means. Neonaucleoside A and its C-3 epimer were prepared from secologanin and tryptamine.

Topics: Glycosides; Indole Alkaloids; Iridoid Glucosides; Iridoids; Nuclear Magnetic Resonance, Biomolecular; Plant Roots; Rubiaceae; Spectrophotometry, Ultraviolet; Stereoisomerism; Tryptamines

A transgenic Saccharomyces cerevisiae was constructed containing the cDNAs coding for strictosidine synthase (STR) and strictosidine beta-glucosidase (SGD) from the medicinal plant Catharanthus roseus. Both enzymes are involved in the biosynthesis of terpenoid indole alkaloids. The yeast culture was found to express high levels of both enzymes. STR activity was found both inside the cells (13.2 nkatal/g fresh weight) and in the medium (up to 25 nkatal/l medium), whereas SGD activity was present only inside the yeast cells (2.5 mkatal/g fresh weight). Upon feeding of tryptamine and secologanin, this transgenic yeast culture produced high levels of strictosidine in the medium; levels up to 2 g/l were measured. Inside the yeast cells strictosidine was also detected, although in much lower amounts (0.2 mg/g cells). This was due to the low permeability of the cells towards the substrates, secologanin and tryptamine. However, the strictosidine present in the medium was completely hydrolyzed to cathenamine, after permeabilizing the yeast cells. Furthermore, transgenic S. cerevisiae was able to grow on an extract of Symphoricarpus albus berries serving as a source for secologanin and carbohydrates. Under these conditions, the addition of tryptamine was sufficient for the transgenic yeast culture to produce indole alkaloids. Our results show that transgenic yeast cultures are an interesting alternative for the production of plant alkaloids.

Topics: Biotechnology; Carbon-Nitrogen Lyases; Culture Media; Fruit; Genetic Engineering; Glucosidases; Indole Alkaloids; Iridoid Glucosides; Iridoids; Pyrans; Saccharomyces cerevisiae; Transgenes; Tryptamines

A spectrophotometric assay for strictosidine synthase is described. Strictosidine is extracted with ethyl acetate and, where high substrate concentrations are used, the organic extract is washed with dilute ammonia to remove coextracted secologanin; after evaporation of the solvent, the residue is heated with 5 M H2SO4 for 45 min and the A348 value is measured. Strictosidine production is calculated from the response of similarly treated standards. A minimum production of 10-25 nmol of strictosidine may be determined. The assay is demonstrated using extracts of cultured Cinchona ledgeriana cells.

Topics: Carbon-Nitrogen Lyases; Cinchona; Indole Alkaloids; Iridoid Glucosides; Iridoids; Plants, Medicinal; Pyrans; Spectrophotometry, Ultraviolet; Transferases; Tryptamines; Vinca Alkaloids