Enzymatic resolution of dioxygenated dicyclopentadienes: Enantiopure hydrindanes, hydroisoquinolones, diquinanes and application to a synthesis of (+)-coronafacic acid

A 5, 10-dioxygenated-tricyclo[5.2.1.0(2,6)]decane derivative 6 has yielded to efficient enzymatic resolution to provide a range of chiral building blocks, whose absolute configuration has been determined through a total synthesis of naturally occuring (+)-coronafacic acid. (C) 1999 Elsevier Science Ltd. All rights reserved.

Chiral synthons from carvone. Part 53. First enantiospecific synthesis of (-)-9-pupukeanone

The first enantiospecific total synthesis of (-)-9-pupukeanone, starting from (R)-carvone employing a combination of Michael-Michael reaction and an intramolecular rhodium carbenoid C H insertion reaction as key steps, is described. (C) 2002 Elsevier Science Ltd. All rights reserved.

Chiral synthons from carvone, Part 56. Enantiospecific synthesis of (-)-4-thiocyanatoneopupukeanane

Enantiospecific total synthesis of the natural enantiomer of the marine sesquiterpene (-)-4-thiocyanatoneopupukeanane (6) is described. The bicyclo[2.2.2]octanonecarboxylate 11, obtained from (R)-carvone and methyl methacrylate via Michael-Michael reaction, was transformed into bicyclo[2.2.2]octenecarboxylic acid 8. Intramolecular cyclopropanation reaction of the diazo ketone 7, derived from the acid 8, followed by regioselective reductive cyclopropane ring cleavage generated neopupukeanol 20, which was transformed into (-)-4-thiocyanatoneopupukeanane 6.

Radical cyclization strategies to terpenoids; syntheses of (±)-β-cuparenone, (±)-laurene and epilaurenes

Radical cyclization of the bromide Image , obtained in 5 steps from the ketone Image , furnished exclusively Image Image 6-endo trig cyclization with out any observable amount of 5-exo trig product Image . 5-Exo dig radical cyclizatlon of the bromo acetate Image , prepared from Image Image the aldehyde Image , followed by routine transformations furnished the cyclopentenone Image , an immediate precursor to β-cuparenone (Image ). Similarly, total synthesis of laurenes Image and Image was achieved Image the 5-exo dig radical cyclization of the xanthate Image , obtained from the aldehyde Image .Syntheses to title compounds based on 5-exo-dig radical cyclisation, along with two unsuccessful approaches to cuparene, are described.

Synthetic approaches to homogynolides A and B

A four step, efficient and general methodology for the conversion of a cyclic ketone into the corresponding alpha-spiro-beta-methylene-gamma-butyrolactone, the key structural feature present in tricyclic sesquiterpenes bakkanes, has been developed employing a regiospecific 5-exo dig radical cyclisation reaction as the key step. The methodology has been extended to the total synthesis of bakkanes including homogynolide-B and chiral homogynolide-A.

Enantioselective formal total syntheses of Clavukerin A and isoclavukerin A via a ring-closing metathesis reaction

Enantioselective formal total syntheses of the marine trisnorsesquiterpenes clavukerin A and isoclavukerin A, starting from (R)-limonene employing an RCM reaction as the key step, are described.

Enantioselective and Protecting Group-Free Synthesis of 1-Deoxythionojirimycin, 1-Deoxythiomannojirimycin, and 1-Deoxythiotalonojirimycin

1-Deoxythioglyconojirimycins were synthesized by using a protecting group-free strategy, starting from readily available carbohydrates, in good overall yield. Use of benzyl-triethylammonium tetrathiomolybdate, BnEt3N](2)MoS4, as a sulfur transfer reagent and borohydride exchange resin (BER) reduction of a lactone enabled the efficient synthesis of the title compounds.

Enantioselective Synthesis of Possible Diastereomers of Heptadeca-1-ene-4,6-diyne-3,8,9,10-tetrol; Putative Structure of a Conjugated Diyne Natural Product Isolated from Hydrocotyle leucocephala

Enantioselective synthesis of possible diastereomers of heptadeca-1-ene-4,6-diyne-3,8,9,10-tetrol, a structure proposed for the natural product isolated from Hydrocotyle leucocephala is accomplished. The reported spectral data of the natural product did not match those of any of the isomers that were synthesized and established that the structure proposed for the natural product is not correct and requires revision.

Enantioselective synthesis of both (+)- and (-)-derivatives of bicyclo[4.3.0]nonan-8-one and 3,8-diones from R-carvone

Enantioselective synthesis of both the enantiomeric forms of the hydrindane derivatives mentioned in the title, potential chiral precursors in terpenoid synthesis, starling from R-carvone employing two different cyclopentannulation methodologies is described.

A new strategy for the alpha-vinylation of ketones: Application to an enantioselective synthesis of sesquiterpene (+)-alpha-elemene

A new, simple and preparatively useful protocol for the construction of a-vinyl ketones, particularly those bearing a quaternary carbon centre, from the corresponding alkenes has been devised. Our four-step strategy consists of dichloroketene addition, base catalysed ring contraction to 'push-pull' cyclopropane esters, reduction and eliminative cyclopropane fragmentation to unravel the a-vinyl ketone moiety. The generality of this approach has been demonstrated with a few representative olefins and good regio- and stereocontrol has been observed. As an application of this methodology, an enantioselective synthesis of sesquiterpene hydrocarbon (+)-alpha-elemene (42) from R-(+)-limonene (43) has been accomplished.

A catalytic michael/horner-wadsworth-emmons cascade reaction for enantioselective synthesis of thiochromenes

A catalytic enantioselective sulfa-Michael/Horner-Wadsworth-Emmons reaction cascade has been developed, taking advantage of phosphonate as an electrophilic activator and a traceless binding site. Using a chiral bifunctional urea derivative as the catalyst, a variety of aryl and heteroaryl substituted thiochromenes was obtained in excellent yield with a high level of enantioselectivity.

Enantioselective synthesis of macrolactone core of the natural product Sch725674

An enantioselective synthesis of the macrolactone core of natural product Sch725674 was accomplished from furfural. Key reactions in assembly of the macrolactone are the use of furan as a but-2-ene-dione equivalent and ring closing metathesis. (C) 2014 Elsevier Ltd. All rights reserved.

Catalytic Aldol-Cyclization Cascade of 3-Isothiocyanato Oxindoles with alpha-Ketophosphonates for the Enantioselective Synthesis of beta-Amino-alpha-hydroxyphosphonates

A cascade aldol cyclization reaction between 3-isothiocyanato oxindoles and alpha-ketophosphonates has been developed for the synthesis of beta-amino-alpha-hydroxyphosphonate derivatives. Catalyzed by a quinine-based tertiary amino-thiourea derivative, this reaction delivers 2-thioxooxazolidinyl phosphonates based on a spirooxindole scaffold bearing two contiguous quaternary stereogenic centers in high yields with excellent diastereo- (up to >20:1 dr) and enantioselectivities (up to >99:1 er).

Variations in the levels of aminoacylation and modified nucleotide content between total tRNAs from chloroplasts and etioplasts in cucumber cotyledons

Total tRNAs isolated from chloroplasts and etioplasts of cucumber cotyledons were compared with respect toamino acid acceptance, isoacceptor distribution and extent of modification. Aminoacylation of the tRNAs with nine different amino acids studied indicated that the relative acceptor activities of chloroplast total tRNAs for four amino acids are significantly higher than etioplast total tRNAs. Two dimensional polyacrylamide gel electrophoresis(2D-PAGE) of chloroplast total tRNAs separated at least 32 spots, while approximately 41 spots were resolved from etioplast total tRNAs. Comparison of the reversed-phase chromatography (RPC-5) profiles of chloroplast and etioplast leucyl-, lysyl-, phenylalanyl-, and valyl-tRNA species showed no qualitative differences in the elution profiles. However, leucyl-, lysyl- and valyl-tRNA species showed quantitative differences in the relative amounts of the isoaccepting species present in chloroplasts and etioplasts. The analysis of modified nucleotides of total tRNAs from the two plastid types indicated that total tRNA from etioplasts was undermodified with respect to ribothymidine, isopentenyladenosine/hydroxy-isopentenyladenosine, 1 -methylguanosine and 2-o-methylguanosine. This indicates that illumination may cause de novo synthesis of chloroplast tRNAmodifying enzymes encoded for by nuclear genes leading to the formation of highly modified tRNAs in chloroplasts. Based on these results, we speculate that the observed decrease in levels of aminoacylation, variations in the relative amounts of certain isoacceptors, and differences in the electrophoretic mobilities of some extra tRNA spots in the etioplast total tRNAs as compared to chloroplast total tRNAs could be due to some partially undermodified etioplast tRNAs. Taken together, the data suggested that the light-induced transformation of etioplasts into chloroplasts is accompanied by increases in the relative levels of some functional chloroplast tRNAs by post transcriptional nucleotide modifications.