An efficient synthesis of pterosin C and other pterosins

Abstract

A versatile synthetic route to pterosins, sesquiterpenoid indanones present in bracken, Pteridiumaquilinum, has been developed. The route is exemplified by the synthesis of (2S,3S)-pterosin C by Friedel–Crafts bisacylation of the methyl ether of 2-(2,6-dimethylphenyl)ethanol with methylmalonyl chloride. Demethylation of the resulting 1,3-indandione and reduction with zinc and acetic acid in the presence of acetic anhydride and sodium acetate afforded a mixture of racemic cis and trans isomers of pterosin C diacetate, which was hydrolysed to the corresponding pterosins. Separation and resolution via the S-(+)-α-phenylbutyric esters gave (2S,3S)-pterosin C and (2R,3R)-pterosin C. Other pterosins were prepared as racemates from the 1,3-indandione.

Isolation and characterisation of 13 pterosins and pterosides from bracken (Pteridium aquilinum (L.) Kuhn) rhizome

“…X-ray data for the two known pterosides (31 and 35) confirmed the absolute configuration determined previously by CD, i.e. (2R)-pteroside B (31) and (2S)-pteroside K (35) (Fukuoka et al, 1978;Kuroyanagi et al, 1979;Ng and McMorris, 1984) (Figs. 2 & 7,SI2, and deposited with the Cambridge Crystallographic Data Centre).…”

Variation in ptaquiloside content in bracken (Pteridium esculentum(Forst. f) Cockayne) in New Zealand

“…Pta-like substances and their products of hydrolysis, the pterosins, have been identifi ed in some basidiomycetes, e.g. either one or both of illudin S and M from Omphalotus illudens and O. olearis (McCloud et al 1996) and pterosins in Fomes annosus and Cyathus bulleri (Ng and McMorris 1984). Pta has been found in ferns grown in sterilised potting soil, and may be present in even higher concentrations than in similar ferns grown artifi cially in non-sterilised bracken soil (Smith et al 1990).…”

Final‐Stage Site‐Selective Acylation for the Total Syntheses of Multifidosides A–C

“…[10] Aretrosynthetic analysis for natural glycosides 5a-c [5a: (2S,3S)-wallichoside, 5b:( 2 R,3S)-wallichoside, 5c:p teroside B],t he precursors of the target natural glycosides 1-3,i s shown in Scheme 1. [11] Thetotal synthesis of 2 was investigated first (Scheme 2). Theaglycons 7a, 7b,and 9 are also natural products known as (2S,3S)-pterosin C, (2R,3S)-pterosin C, and (2R)-pterosin B, [10] respectively.T he b-hydroxyketone moieties of 7a and 7b could be constructed by an organocatalytic intramolecular asymmetric aldol reaction of the aromatic ketoaldehyde 11.A lthough the relative stereochemistry of the aldol reaction could not be predicted at this stage,b oth the syn and anti isomers were required because they are both constituents of the natural products, and the interconversion between them seemed possible by epimerization at C2.…”

“…Theaglycon 9 would be readily obtained by reductive removal of the hydroxy group of 7b. [11] Thetotal synthesis of 2 was investigated first (Scheme 2). Thea ldol precursor 11 was prepared from the commercially available tetrasubstituted benzene 12.C onsecutive lithiumhalogen exchange/hydroxyethylation and lithium-halogen exchange/formylation of 12 afforded at risubstituted benzaldehyde derivative,which was then underwent reduction of the formyl group and methoxycarbonylation of the resulting alcohol to give 13.After iodination of 13 with I 2 and PIFA, [12] intramolecular Ot oCacyl migration of the aryl magnesium species,g enerated by iodine-magnesium exchange of the resulting aryl iodine,a nd subsequent methanolysis gave the lactone 14.P rotection of the primary hydroxy group of 14 with aT BDPS group,a ddition of aG rignard reagent to the lactone,a nd Ley oxidation [13] of the resulting lactol gave 11.…”