Luigi Canonica

Evidence about the catecholoxidase activity of the enzyme ascorbate oxidase extracted from Cucurbita pepo medullosa

Pure ascorbate oxidase (L-ascorbate:oxygen oxidoreductase, EC 1.10.3.3) isolated from Cucurbita pepo medullosa, which is known to be specific for ascorbic acid, shows a secondary catecholoxidase activity at approx. pH 6.7. This activity was tested against natural and synthetic compounds possessing a catechol-like structure. Among natural compounds (+)-catechin furnishes the same complex oxidation mixture obtained with other oxidases. Among synthetic compounds, 3,5-di-t-butylcatechol and 4-t-butylcatechol give the corresponding o-quinones. The significance of this secondary activity in the darkening process of fruits and vegetables which contain ascorbate oxidase is also discussed.

A novel method of isolation of phytoecdysones from kaladana seeds

Abstract A new simplified technique is described for the isolation and separation of phytoecdysones from kaladana seeds. Using this method ecdysone, crustecdysone, muristerone A, kaladasterone, calonysterone and makisterone A were obtained. In addition methyl 3,4-dihydroxycinnamate was found in the seed.

Unusual photochemical behaviour of the enone chromophore of the insect moulting hormone 20α-hydroxyecdysone

U.v. irradiation of the most representative insect moulting hormone 20α-hydroxyecdysone (1) in follows two unusual pathways the reduction products (2) and (4)(path a) together with the ketone (5) and the cyclobutanol(6)(path b).

Biosynthesis of mycophenolic acid

Incorporation experiments with labelled potential biosynthetic intermediates suggest that the methyl group at C-4 of the phthalide system in mycophenolic acid is introduced at the tetraketide stage. This then gives way to the aromatic system, which is further oxidised to 5,7-dihydroxy-4-methylphthalide. The isolation of 6-farnesyl-5,7-di-hydroxy-4-methylphthalide from the culture and the high incorporation of this compound into mycophenolic acid indicate that the most important process for the biosynthesis of the side-chain is the introduction of a C15 terpene chain followed by oxidative fission at the appropriate double bond. ‘Enzymic trap’ experiments confirm these results. Alternative pathways for the biosynthesis of the side-chain through 6-geranyl-5.7-dihydroxy-4-methyl-phthalide are discussed.

Fate of the 16β-hydrogen atom of cholesterol in the biosynthesis of tomatidine and solanidine

During the biosynthesis of tomatidine (1) in Lycopersicon pimpinellifolium, the 16β-hydrogen atom of cholesterol is inverted to the 16α-position; the same hydrogen atom is lost during the biosynthesis of solanidine (2) in Solanum tuberosum.

Incorporation of 5α-furostan-3β,26-diol into tigogenin by Digitalis lanata

Abstract 2,2′,4,4′-3H4-dihydrotigogenin was converted by Digitalis lanata plants into tigogenin.

Studies on proaporphine and aporphine alkaloids. Part V. Synthesis of (±)-glaziovine by 8,1′-ring closure of 1-benzylisoquinoline derivatives

A new, convenient synthesis of (±)-glaziovine (N-methylcrotsparine)(1) has been devised, involving as the key steps the nitration of (±)-4′-O-benzyl-N-methylcocclaurine (21), followed by catalytic hydrogenation to (±)-8-amino-N-methylcoclaurine (23), diazotization, and irradiation of the o-diazo-oxide (24). The synthesis of (±)-glaziovine by irradiation of (±)-8-bromo-N-methylcolaurine has been reinvestigated and improved. An attempted phenolic coupling reaction of (±)-N-trifluoroacetylcrotsparine (2) by vanadium oxide trichloride resulted in 8-chlorination and 4-hydroxylation [to give compounds (8) and (9)].

Studies on proaporphine and aporphine alkaloids. Part VI. Synthesis of (±)-glaziovine by spiran ring construction on a cyclopent[ij]isoquinoline; stereochemistry of reduced proaporphines

The Wittig reaction of methoxymethyltriphenylphosphonium chloride (11) with 2,3,8,8a-tetrahydro-6-hydroxy-5-methoxy-1-methylcyclopent[ij]isoquinolin-7(1H)-one (4), obtained from 1,2,3,4-tetrahydro-6,7-dimethoxy-2-methylisoquinoline-1-acetic acid (6) and polyphosphoric acid, gave the Z-enol ether (17) and, by hydrolysis, the cyclopent[ij]isoquinoline-7-carbaldehyde (19); the latter afforded (±)-11,12-dihydroglaziovine (20), along with a small amount of the 8,9-dihydro-isomer (21), on ring formation with methyl vinyl ketone, catalysed by 1,5-diazabicyclo[5.4.0]undec-5-ene. Bromination of the O-acetate of (20), followed by dehydrobromination, yielded (±)-glaziovine (1). The relative configurations of the asymmetric centres of compounds (20) and (21), as derived from an X-ray crystallographic analysis of the hydrobromide of (20), provide a reference in the stereo-chemistry of reduced proaporphines, such as amuronine (16), to which a revised (6aS,7aS)-configuration has been assigned.

Structure of calonysterone, an unusually modified phytoecdysone

The structure of 2β,3β,6,20R, 22R,25-hexahydroxycholesta-5,8(9),14-trien-7-one (I) has been assigned to calonysterone, a phytoecdysone isolated from kaladana (I pomoea sp.), by 13C and 1H n.m.r. spectroscopy.

Structure of muristerone A, a new phytoecdysone

Muristerone A, a new phytoecdysone isolated from I pomoea calonyction(Choisy) Hallier f. sp. nova, has been identified as 2β,3β,5β,11α,14α,20R,22R-hepta-hydroxycholest-7-en-6-one.