720. West african timbers. Part IV. Some reactions of gedunin

Abstract

Some reactions of gedunin are described, and it is shown that they are explained by a structure (11) similar to that recently proved for limonin.RECENTLY we described 1 the isolation of gedunin from the timber of Entandrophragma angolense. The formula C28H34(36)07 was assigned to this compound, and it was shown that on hydrogenation over palladised charcoal it gave a dihydro-derivative, which we have also obtained as a natural product from several timbers2 It was also shown that on steam-distillation from alkali gedunin gave furan-3-aldehyde which was isolated as its dinitrophenylhydrazone. The reactions now described indicate that the formula is C,,HM07.Gedunin shows absorption maxima in the ultraviolet (Am,, 215 and 335 mp, log E 4-12 and 1.8) and in the infrared region (1668 cm.-l) consistent with the presence of an a@unsaturated ketone group, and gives a red dinitrophenylhydrazone. The spectrum of dihydrogedunin does not show these characteristics, but has a new band a t 1709 cm.-l, suggesting that it is the corresponding saturated ketone. The maximum at 215 mp is due to absorption by both the @-unsaturated ketone group and the furan ring. When the spectrum of dihydrogedunin, which still has the furan ring (vmax. 1502 and 875 cm.-l), is subtracted from that of gedunin, the maximum for the unsaturated ketone appears at 227 mp (log E 4-0).The molecular-rotation difference between gedunin and dihydrogedunin is -173", in agreement with the change of -162" between 1,2-dehydrohinokione and hinokione, a 3-0xo-diterpene.~ (In ref. 1 the rotation of gedunin and of dihydrogedunin is given with the wrong sign, asinstead of +). Reduction of gedunin with sodium borohydride gave an alcohol which on re-oxidation with chromic acid in acetone gave dihydrogedunin. The molecular-rotation difference between dihydrogedunin and the borohydride reduction product was -110", in agreement with the change of -85" between p-amyrone and @-amyrin. This unusual reduction of an unsaturated ketone to the corresponding saturated alcohol has been reported by Albrecht and Tamm5 in the case of cholest-1-en3-one, and we consider that the evidence suggests that gedunin is a 3-oxo-Al-triterpene derivative.The maximum of cholest-1-en-3-one is at 230 mp (log E 4.0).Further evidence on this is described below.

Synthesis and antibacterial activity of 7-deacetoxy-7-hydroxygedunin

“…The novel protocol reported here for the synthesis of 7-deacetoxy-7α-hydroxygedunin gave higher yield 88% and did not require column chromatographic purification compared with previously reported method that gave 43.4% yield (Akisanya et al, 1961).…”

“…The pure 7-deacetoxy-7α-hydroxygedunin was obtained in 43.4% w/w yield (Akisanya et al, 1961). Naturally occurring 7-deacetoxy-7α-hydroxygedunin along with other hydroxylated gedunin derivatives were isolated from Cedrela sinensis (Mitsui et al, 2006) and from the root and leaf of Cedrela fissilis (Alessandra et al, 2006).…”

Phytochemistry and pharmacology of the genus Entandrophragma over the 50 years from 1967 to 2018: a ‘golden’ overview

“…It was firstly obtained from E. angolense and later from E. delevoyi . Compound 12 was characterized as being structurally close to the known limonin by some chemical transformations . Its relative stereochemistry and constitution were confirmed by X‐ray analysis of the dihydrogedun‐3β‐yl iodoacetate derivative .…”

“…The opening of ring D is done via ring expansion by a Baeyer–Villiger‐type oxidation . Gedunin ( 12 ) was the first isolated and documented limonoid from the family Meliaceae . It was firstly obtained from E. angolense and later from E. delevoyi .…”

“…[19] Gedunin (12) was the first isolated and documented limonoid from the family Meliaceae. [6,20] It was firstly obtained from E. angolense [6] and later from E. delevoyi. [17,21] Compound 12 was characterized as being structurally close to the known limonin by some chemical transformations.…”