The four-carbon elongation of three-carbon chiral synthons using 2-(trimethylsiloxy)furan: highly stereocontrolled entry to enantiomerically pure seven-carbon α,β-unsaturated 2,3-dideoxy-aldonolactones

The first total synthesis and revision of absolute stereochemistry of natural cytotoxic lactone cleistanolate

Development of a synthetic route applicable to d-ribose and d-xylose enabled the synthesis of cleistanolate putative structure, its five stereoisomers, and led to revision and confirmation of absolute stereochemistry of the natural product. Key steps of the synthesis included zinc-mediated THF ring-opening and stereoselective dihydroxylation under the Upjohn conditions. The first total synthesis of cleistanolate was completed in eight steps starting from d-xylose. The C-5 stereocenter of the natural product was assigned the correct (5S)-stereochemistry. Cytotoxicity of natural product was briefly investigated.

Efficient synthesis of the C(1)-C(9) fragment of amphidinolides C, C2, and F

The synthesis of the C(1)-C(9) fragment of amphidinolides C, C2, and F was achieved by using a vinyloguous Mukaiyama aldol reaction on a chiral aldehyde with a silyloxyfuran and by using a C-glycosylation of a lactol derivative with an acetyl oxazolidinethione. From the available chiral acetonide-glyceraldehyde, all the stereogenic centers were perfectly induced along the synthesis. The C(1)-C(9) fragment was synthesized as a vinyl stannane at C(9) in 10 steps, with 16% yield.

Aminocyclopentanols as sugar mimics. Synthesis from unsaturated bicyclic lactones by Overman rearrangement

Bicyclic cyclopentane lactones, prepared from bromodeoxyaldonolactones, were transformed into aminocyclopentanols with an Overman rearrangement as the key step. Two of the compounds prepared, 7 and 19, were found to be good inhibitors of jack bean alpha-mannosidase and beta-D-N-acetylglucosaminidase, respectively.

The utility of furan-, pyrrole-, and thiophene-based 2-silyloxy dienes as demonstrated by modular synthesis of annonaceous acetogenin core units and their pyrrolidine and thiolane analogues

We report a modular strategy for obtaining the core units of annonaceous acetogenins and their nitrogen and sulfur analogues, which generates great structural diversity. This synthesis is based on the application of a reiterative vinylogous addition protocol involving a unique triad of silyloxy diene modules, 2-[(tert-butyldimethylsilyl)oxy]furan (TBSOF), N-(tert-butoxycarbonyl)-2-[(tert-butyldimethylsilyl)oxy]pyrrole (TBSOP), and 2-[(tert-butyldimethylsilyl)oxy]thiophene (TBSOT) and suitable heteroatom-stabilized carbenium ions. By combining TBSOF, TBSOP, and TBSOT nucleophilic synthons with certain tetrahydrofuran, pyrrolidine, and thiolane acceptors, the construction of varied, adjacently linked oligo-heterocyclic motifs related to the core segments of the annonaceous acetogenins is assured. At first, the reliability of the pivotal coupling maneuver was certified, by assembling a collection of 18 model constructs, covering all oxygen, nitrogen, and sulfur heteroatom combinations (i.e., compounds 7-9, 13-15, and 19-21). This uniformed protocol was then suited to forge advanced bis-tetrahydrofuran, bis-pyrrolidine, and bis-thiolane scaffolds encompassing the heterocyclic core portion of various binuclear annonaceous acetogenins and relatives. The utility of this synthesis was demonstrated by the preparation of a repertoire of eight isomeric bis-tetrahydrofuran units, 41-48, two bis-pyrrolidine units, 62 and 63, and four bis-thiolane units, 78-81.

Expeditious syntheses of sugar-modified nucleosides and collections thereof exploiting furan-, pyrrole-, and thiophene-based siloxy dienes

A series of individual sugar-modified pyrimidine nucleosides including enantiomerically enriched 2',3'-dideoxynucleosides 14a-c (alpha and beta anomers of L- and D-series), 2',3'-dideoxy-4'-thionucleosides 21a-c (alpha and beta anomers of L- and D-series), and 2',3'-dideoxy-4'-azanucleosides 28a-c (beta anomers of L- and D-series) were synthesized, with uniform chemistry and high stereochemical efficiency, exploiting a triad of versatile heterocyclic siloxy dienes, namely, 2-(tert-butyldimethylsiloxy)furan (TBSOF), 2-(tert-butyldimethylsiloxy)thiophene (TBSOT), and N-(tert-butoxycarbonyl)-2-(tert-butyldimethylsiloxy)pyrrole (TBSOP). The synthetic procedure advantageously used both enantiomers of glyceraldehyde acetonide (D-1 and L-1) as sources of chirality and as synthetic equivalents of the formyl cation. The outlined chemistry also allowed for the rapid assemblage of a 30-member collection of racemic nucleosides (D,L-L) as well as one 15-member ensemble of chiral analogues (L-L), along with some related sublibraries.

The synthesis of 5-C-(6-deoxy-1,2:3,4-di-O-isopropylidene-alpha-D-galactopyranos-6-yl)-2 ,3-O-isopropylidene-D-allo-pentofuranose [deaminotri-O-isopropylidene tunicamine]

Three approaches to the synthesis of deaminotunicamine and derivatives were developed. Tin tetrachloride condensation of 6-deoxy-1,2:3,4-di-O-isopropylidene-alpha-D-galacto-heptodialdo-1, 5-pyranose with 2-(trimethylsilyloxy)furan gave a mixture of stereoisomeric precursors. Condensation of 1,2:3,4-di-O-isopropylidene-alpha-D-galacto-hexodialdo-1,5-pyranos e with the phosphate carbanion obtained from diethyl (2-furyl)methoxymethyl phosphonate led to 6-deoxy-7-C-(2-furyl)-1,2:3,4-di-O-isopropylidene-L-glycero-alpha-D- galactoheptopyranose (13). This was converted, via the "delta 2"-butenolide route, to a mixture of stereoisomeric 5-C-(6-deoxy-alpha-D-galactopyranos-6-yl)-pentono-1,4-lacton es of the D-allo and D-talo configuration. In the third approach, 13 was transformed by the "enulose" approach to deamino-tri-(O-isopropylidene)tunicamine.