Structures of indole alkaloids from Strychnos angustiflora

by Au, Tak-yan

(Uncorrected OCR) ?Abstract of thesis entitled "Structures of Indole

Alkaloids from Strychnos angustiflora" submitted by ~

AU Tak-yan, Francis for the degree of Master of Science at the University of Hong Kong in March 1973.

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ABSTRACT

From the leaves of Strychnos angustiflora Benth,three orange-coloured alkaloids angustoline, angus tine and angustidine have been isolated in low yield.

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Molecular formulae and electronic spectra

indicate that all three alkaloids have the same highly

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conjugated polycyclic skeleton.

Structure~ shown below

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are proposed?

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Alkaloid Formula Rl R2 Angustoline C2'OH1702N3 CH(OH)CH3 H Angustine C20'H1SON3 CH=CH2 ! Angustidine Cl9H1SON3 H CH3 The major alkaloid, angustoline, is monoacidic and the hydrochloride-and the picr~te sa~ts have been prepared.

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The presence of a l-hydroxyethyl side chain shown by n.m.r. has been confir.med by acetylation to g~ve an

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acetate.

Chemical correlation between angustoline and angustine has been achieved in two ways. Firstly, the

former was converted to the latter 'by acidic catalysed dehydration ? Secondly, an~ustoline or its acetate on heating with collidine yielded dihydroangustine, also obtained from angustine by hydrogenation.

Arguments are presented for the structures of the three alkaloids, based substantially on n.m.r. data

(including long-range coupling and N.O.E. data) and biogenetic considerations.

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The three alkaloids are postulated to be derived biogenetically from vincoside, the fused pyridine ring being formed via opening of the iridoid glycoside ring by ammonia (or equivalent).