Naotaka Nagakura

The biosynthesis of monoterpenoid indole alkaloids from strictosidine

The differential incorporation of doubly labelled strictosidine and vincoside into several indole alkaloids belonging to the Corynanthe(3α and 3β series), Aspidosperma, and Iboga types in three plant families has been studied, and it has been demonstrated that only strictosidine is incorporated while vincoside is metabolically inert in these plants with regard to alkaloid formation. During the conversion of strictosidine into the 3β-indole alkaloids, the hydrogen atom at the 3-position is lost, while it is retained during the biosynthesis of the 3α alkaloids. The chemical synthesis of [7-3H]secologanin, an important intermediate for further work in the biosynthesis of monoterpenoid alkaloids, is also described.

S-adenosyl-L-methionine: (S)-scoulerine 9-O-methyltransferase, a highly stereo- and regio-specific enzyme in tetrahydroprotoberberine biosynthesis

Suspension cultures of Berberis species are useful sources for the detection and isolation of a new enzyme which transfers the methyl group from S-adenosyl-L-methionine specifically to the 9-position of the (S)-enantiomer of scoulerine, producing (S)-tetrahydrocolumbamine. The enzyme was enriched 27-fold; it is not particle bound, has a pH optimum of 8.9, a molecular weight of 63 000 and shows a high degree of substrate specificity.

Six tetrahydroisoquinoline-monoterpene glucosides from Cephaelis ipecacuanha

Abstract From the crude drug ‘Ipecac’ (dried root of Cephaelis ipecacuanha) six novel tetrahydroisoquinoline-monoterpene glucosides, 6-O-methylipecoside, ipecosidic acid, demethylalangiside, neoipecoside, 7-O-methyl-neoipecoside and 3,4-dehydroneoipecoside were isolated along with ipecoside, alangiside, sweroside and 7-dehydrologanin. The structures of new glucosides were determined by spectroscopic and chemical means. The biogenesis of these glucosides is also discussed.

Tetrahydroisoquinoline-monoterpene glucosides from Alangium lamarckii and Cephaelis ipecacuanha

Abstract From the dried fruits of Alangium lamarckii, a novel tetrahydroisoquinoline-monoterpene glucoside, 3-O-demethyl-2-O-methylalangiside, was isolated along with alangiside. Re-examination of the constituents of the roots of Cephaelis ipecacuanha led to the isolation and identification of this same compound, as well as alangiside and that of another new glucoside, 7-O-methylipecoside. The structures of these two new glucosides were determined by spectroscopic and chemical means.

Biosynthesis of the protoberberine alkaloid jatrorrhizine

Feeding experiments with distant single or doubly labelled precursors show that the methylene dioxy group of berberine is opened in the formation of jatrorrhizine.

Sambacosides a, e and f, novel tetrameric iridoid glucosides from jasminum sambac

Abstract Structures of three tetrameric iridoid glucosides, sambacosides A, E and F isolated from the leaves of Jasminum sambac (L) Ait. were elucidated as 2, 3 and 4 by chemical and spectrometric means. They represent the first tetrameric iridoid glucosides.

A secoiridoid glucoside from Fraxinus insularis

Abstract A new secoiridoid glucoside, insularoside, was isolated from Fraxinus insularis . The structural elucidation of insularoside by spectroscopic and chemical studies is described. The biogenesis of this glucoside is also briefly discussed.

6′-O-feruloyl- and 6′-O-sinapoyl-demethylalangisides, tetrahydroisoquinoline-monoterpene glucosides from Alangium platanifolium

Abstract From the leaves of Alangium platanifolium var. trilobum , two new tetrahydroisoquinoline-monoterpene glucosides, 6′- O -feruloyl-demethylalangiside and 6′- O -sinapoyl-demethylalangiside, were isolated along with demethylalangiside. Their structures were determined by spectroscopic methods.

Deacetylisoipecoside: the key intermediate in the biosynthesis of the alkaloids cephaeline and emetine

In contrast to previous assumptions, the precursor of the monoterpenoid ipecac alkaloids cephaeline (6) and emetine (5), which arise from the condensation of dopamine (1) and secologanin (2), is α-deacetylisoipecoside (3a) and not its β-epimer deacetylipecoside (4a); the latter is the precursor of ipecoside (4b) and alangiside (7a) both of which possess the β-configuration.

Two phenolic glucosides and an iridoid glucoside from Alangium platanifolium var. Trilobum

Abstract From the leaves of Alangium platanifolium var. trilobum , two new phenolic glucosides, 7- O -methylsalicin and 7- O -(2,6-dihydroxybenzoyl)salicin, and a new iridoid glucoside, 7- O -benzoylloganic acid, were isolated and their structures determined by spectroscopic and chemical studies. Six known compounds isolated for the first time from this plant were identified as salicin, quercetin-3- O -β- d -glucoside, rutin, adenosine, methyl caffeate and roseoside.