Glenn J. McGarvey

Acyclic Stereoselective Synthesis of Carbohydrates

Abstract This review examines recent syntheses of carbohydrates in which the target compounds are viewed as acyclic carbon frameworks. The synthetic approaches are divided into two categories in which critical asymmetry is placed either by (a) stereo-selective carbon-carbon bond formation, or (b) stereoselective carbon-heteroatom bond formation. This account focuses its attention on the methodology utilized to place acyclic stereo-centers as the key feature of the synthetic strategy.

ENZYMES IN ORGANIC SYNTHESIS : RECENT DEVELOPMENTS IN ALDOL REACTIONS AND GLYCOSYLATIONS

Carbohydrates have not been as accessible as other biomolecules such as proteins and nucleic acids and are the least exploited. As a result of their highly asymmetric and densely functionalized nature, carbohydrates are difficult to synthesize using conventional chemistry. Enzymatic synthesis, however, with its high selectivity and mild reaction conditions is very useful for the preparation of carbohydrates. This review gives a brief overview of recent developments in the application of enzymatic aldol reactions and glycosylations to carbohydrate synthesis.

Polyene synthesis: A comparative study

Abstract As part of an effort to synthesize the polyene macrolide antibiotics, a comparison of several methods of polyene synthesis has been carried out with the finding that superior results were obtained using the Wollenberg vinyl ether method.

Studies on the stereoselective synthesis of C-allyl glycosides.

An investigation was carried out to explore the use of sulfoxide donors as common precursors to stereoisomeric C-glycoconjugates of glycoprotein and glycolipid tumor antigens. A study focusing on the effects of reaction conditions and substrate structure on the stereoselectivity of allylation was carried out. Although conditions were realized to selectively afford alpha-allylation products in good to excellent yields, the search for conditions favoring beta-selectivity proved less successful.

Development of chiral β-dicarbonyl equivalents. Enantiodivergent alkylation of aspartic acid.

Abstract L-Aspartic acid has been converted to derivatives which undergo alkylation reaction with stereoselectivities that are enantiomerically complimentary.

Cis- and trans-1,7,9-trioxadispiro[5.1.5.3]hexadecane: Synthetic studies

Abstract The first synthesis of the title compounds via thermodynamic spirocyclization of a diketodiol 2 is described. Three convergent synthetic approaches to protected derivatives of 2 have been developed, all of which have been converted into a 1.70:1.00 mixture of trans -3: cis -3. A practical consequence of these studies is the availability of the title compounds from dihydropyran and 1,5-pentanediol in 28% and 32% overall yields, respectively.

2-phenyloxazolines as carboxylate precursors - applications to the synthesis of asymmetric branched-chain structures

Abstract A synthetic approach to the title compounds is presented that features the asymmetric elaboration of a chiral, non-racemic oxazoline followed by a two-step oxidative ring cleavage of the heterocycle to a triamide for further transformation.

Studies on the stereoselective hydroboration of vinyl ethers

Abstract The diastereoselective hydroboration/oxidation of several asymmetric vinyl ethers is presented.

Synthesis of α- and β-C-glycosides of N-acetylglucosamine

Abstract As part of efforts to make available new classes of bioactive C-glycoconjugates, d -glucosamine has been effectively converted into a series of 2-deoxy-2-amino-C-glycosides. This versatile approach is keyed by a remarkably effective metal catalyzed olefin isomerization of the isomeric C-allyl amino sugars which, in turn, are readily available via radical allylation of d -glucosamine.

Cis- and trans-1,7,9-trioxadispiro[5.1.5.3]hexadecane: Stability studies and solution structures

Abstract The stability of cis- and trans-1,7,9-trioxadispiro[5.1.5.3]hexadecanes was examined through equilibration studies with the result that the trans-isomer was more stable by 0.3–0.7 kcal/mol, depending upon the solvent. NMR studies indicate that the central ring of these compounds is in a twist-boat conformation in solution which allows these isomers to best accommodate conflicting steric and electronic effects on their stability.