Stereoselective formal synthesis of the potent proteasome inhibitor: salinosporamide A

(2R,3S)-α-Methylenelactam 3, the key intermediate in Corey’s syntheses of salinosporamide A, has been synthesized from (S)-methyl 2-hydroxymethylpyroglutamate through chemoselective O-protection, regio- and stereoselective N-methylnitrone cycloaddition and quaternarization-elimination reactions as the main steps.     

Stereoselective synthesis of scyphostatin hydrophilic moiety

A stereoselective synthesis of scyphostatin hydrophilic moiety was accomplished. Substrate- and reagent-controlled dihydroxylation of tri- and monosubstituted alkenes afforded desired diols, respectively. Chemo- and stereoselective allylation of α-(methoxycarbonyl)cyclohexanone provided allylcyclohexanol. Oxidative cleavage of glycol and subsequent β-elimination of siloxycyclohexanone furnished the desired epoxycyclohexenone.     

Total synthesis of salinosporamide A

The total synthesis of salinosporamide A has been achieved through enzymatic desymmetrization, diastereoselective aldol reaction, intramolecular aldol reaction, and intermolecular Reformatsky-type reaction followed by 1,4-reduction as key reactions.     

Total synthesis of salinosporamide A

Total synthesis of potent proteasome inhibitor salinosporamide A (1) has been accomplished, which features strictly substrate-controlled operations starting with the only chiral center of (R)-pyroglutamic acid. The consecutive quaternary carbons within 1 have been efficiently constructed by manipulation of two intramolecular reactions: (1) carbonate-mediated internal acylation of imidate ester (4 --> 14) and (2) selenocyclization of aldehyde to exocyclic methylene group (5 --> 18).     

Stereoselective synthesis of heterosubstituted aziridines and their functionalization

Lithiated (α-chloroalkyl)heterocycles, generated by deprotonation with LDA at −78 °C in THF, add to various enantiopure imines affording ‘one pot’ chiral heterosubstituted aziridines in a diastereoselective manner. Lithiated heterosubstituted aziridines, obtained by deprotonation of the corresponding aziridines with n-BuLi at −78 °C in THF, were trapped by electrophiles (D₂O or CH₃I) with high stereoselectivity.     

A simple stereocontrolled synthesis of salinosporamide A

A simple and effective stereocontrolled synthesis of salinosporamide A has been developed. This process, the first synthesis of salinosporamide A, is capable of providing the compound in substantial quantities for further biological studies. Salinosporamide A was of special interest as a synthetic target because of its potent in vitro cytotoxic activity against many tumor cell lines (IC(50) values of 10 nM or less).     

A concise total synthesis of salinosporamide A

A concise and straightforward 14-step total synthesis of (+/-)-salinosporamide A, based on a diastereoselective acid-catalysed intramolecular cyclisation of to the pyrrolidinone , and a regioselective reduction of the malonate derivative 8b to the aldehyde 9, is described.     

Stereoselective synthesis and functionalization of 4-heterosubstituted β-lactams

Polyfunctionalized β-lactams were prepared with high stereoselectivity in an efficient manner. A palladium-catalyzed [2+2] carbonylative cycloaddition of allyl bromide with heteroaryliden-anilines afforded 2-azetidinones N-phenyl substituted, with an heteroaryl moiety linked at the C-4 carbon, and an alkenyl group at the C-3 carbon. The C-3 and the C-4 positions could be further functionalized inserting alkyl and hydroxyl groups in the azetidinone ring, through the generation of a stable azetidinyl anion then captured by various electrophiles.     

Stereoselective synthesis and functionalization of N-alkyl-β-lactams

Novel polyfunctionalized N-alkyl-β-lactams were prepared with high stereoselectivity in an efficient manner by a palladium-catalyzed [2+2] carbonylative cycloaddition of allyl bromide with heteroarylidene N-alkyl-amines The type of alkyl group linked to the nitrogen atom influences the reaction stereoselectivity. Moreover, the C-3 and the C-4 positions of the azetidinone ring can be further stereoselectively functionalized inserting various groups through the generation of a stable azetidinyl carbanion and then captured by various electrophiles.     

Adsorption-desorption behavior of phenols on novel polymers containing the pyrrolidinone moiety

Crosslinked polymers having a pyrrolidinone moiety (CPS, CPES, and CVP) were synthesized by radical copolymerization of 4-(2-oxo-1-pyrrolidinyl)methylstyrene, 4-[2-(2-oxo-1-pyrrolidinyl)ethoxy]methylstyrene, or 2-vinylpyrrolidinone with divinylbenzene in the presence of AIBN as a radical initiator. The adsorption-desorption behavior of phenols on these polymers was investigated. The polymers with spacers between the polymer main chain and pyrrolidinone moiety appeared to have a superior adsorption capability to those without such spacers. The amount of phenol adsorbed on the polymers in a solvent decreased in the following order: water > chloroform > methanol. In methanol, the interaction between the polymers and phenol was suggested to come only from charge-transfer stacking (C–T stacking), whereas in chloroform the interaction was caused mainly by both hydrogen bonding and C–T stacking. The interaction in water was attributed not only to both hydrogen bonding and C–T stacking, but also to a hydrophobic interaction. Characterization of polymers (CVP) containing adsorbed phenol was carried out by thermogravimetric analysis (TGA). The TGA curves indicated a two step weight-decrease, namely the first step in the temperature ranging from ca. 100-200°C was attributed to the desorption of phenol while the second step in the temperature ranging from ca. 350-500°C was based on thermal decomposition of the polymers. The desorption of phenol adsorbed on the polymers in water indicated an inverse tendency to the adsorption; that is, the amount of phenol desorbed from the polymers without a spacer was more than those from the polymers with spacers. © 1994 John Wiley & Sons, Inc.     

Formal synthesis of salinosporamide A via NHC-catalyzed intramolecular lactonization

An N-heterocyclic carbene (NHC) catalyzed intramolecular lactonization to prepare densely functionalized bicyclic γ-lactam-γ-lactone adducts from enals is reported. This method has been applied to the formal synthesis of salinosporamide A, a potent 20S proteasome inhibitor and anti-cancer therapeutic.     

Studies toward the synthesis of salinosporamide A, a potent proteasome inhibitor

An α-methylenepyrrolidinone bearing all the functionalities and relative configurations of an advanced intermediate in the synthesis of salinosporamide A and analogues has been synthesized from methyl pyroglutamate through regio- and stereoselective N-methylnitrone cycloaddition.     

Progress towards the total synthesis of trichodermamides A and B: construction of the oxazine ring moiety

Trichodermamides are modified heterocyclic dipeptides that possess a unique 4H-5,6-dihydro-1,2-oxazine ring. Starting from affordable, easily available (-)-quinic acid, the enantioselective synthesis of this oxazine moiety was achieved by an intramolecular epoxide ring-opening reaction by an oxime. [structure: see text]     

Stereoselective functionalization of the 1'-position of 4'-thionucleosides

Stereoselective synthesis of novel 1'-alpha-substituted-4'-thionucleosides was achieved starting from D-gulonic acid gamma-lactone via stereoselective nucleophilic substitution.     

Stereoselective synthesis of optically active disilanes and selective functionalization by the cleavage of silicon-naphthyl bonds with bromine

Optically active disilanes with one chiral silicon center, (R)-1,2-dimethyl-1-(naphth-1-yl)-1,2,2-triphenyldisilane and (R)-1,2,2-trimethyl-2-(4-methoxynaphth-1-yl)-1-(naphth-1-yl)-1-phenyldisilane, were obtained by the reaction of (S)-methyl(naphth-1-yl)phenylchlorosilane (> 99% ee) with methyldiphenylsilyllithium or by the reaction of methyldiphenylchlorosilane with optically active (S)-methyl(naphth-1-yl)phenylsilyllithium and by the reaction of (S)-methyl(naphth-1-yl)phenylchlorosilane (> 99% ee) with dimethyl(4-methoxynaphth-1-yl)silyllithium. Under the optimized conditions, the reactions proceeded with almost complete inversion for the cholorosilanes and retention for the silyl anions. Optically active disilanes with two chiral centers, (1R,2R)-1,2-dimethyl-1,2-di(naphth-1-yl)-1,2-diphenyldisilane and (1S,2S)-1,2-di(4-methoxynaphth-1-yl)-1,2-dimethyl-1,2-diphenyldisilane, were obtained in high optical purity by the reactions of corresponding optically active halogenosilanes (Cl or F) with optically active silyllithiums. The silicon-silicon bond and the silicon-naphthyl bond of (R)-1,1,2-trimethyl-1,2-di(naphth-1-yl)-2-phenyldisilane and (1R,2R)-1,2-dimethyl-1,2-di(naphth-1-yl)-1,2-diphenyldisilane were cleaved without selectivity on bromination. The silicon-(4-methoxynaphth-1-yl) bond of (R)-1,2,2-trimethyl-2-(4-methoxynaphth-1-yl)-1-(naphth-1-yl)-1-phenyldisilane was regiospecifically cleaved, followed by the stereoselective cleavage of the remaining chiral silicon-naphthyl bond (94% inversion). Although the silicon-(4-methoxynaphth-1-yl) bonds of (1S,2S)-1,2-di(4-methoxynaphth-1-yl)-1,2-dimethyl-1,2-diphenyldisilane (> 99% ee) were regioselectively cleaved without silicon-silicon bond scission, remarkable racemization could not be avoided during the one-pot reaction.     

Stereoselective synthesis of allylic sulfones via the oxonia-Cope rearrangement of homoallylic alcohols containing a homoallylic sulfone moiety

The homoallylic alcohols 3 that can be prepared by the indium-mediated addition of haloallylic sulfones 1 to aldehydes 2 undergo the oxonia-Cope rearrangement with aldehydes 2 to give rise to the allylic sulfones 4 containing a conjugated diene moiety in a highly stereoselective manner. Electron-rich aldehydes preferentially participate in this oxonia-Cope rearrangement with the homoallylic alcohols 3. Excellent correlations of the stereochemistry (anti-3 to trans-allylic sulfone 4 and syn-3 to cis-allylic sulfone 4) have been observed in the oxonia-Cope rearrangement.     

Stereoselective formal synthesis of aspergillide A

The stereoselective formal synthesis of aspergillide A (1), a cytotoxic 14-membered macrolide, is disclosed. The key intermediate, a trisubstituted tetrahydropyran core is prepared by SmI₂-induced intramolecular reductive cyclization as well as by using sequential α-aminooxylation, Horner-Wadsworth-Emmons olefination, and followed by Oxa-Michael cyclization. Other notable transformations in the synthesis include the use of Jacobsen’s hydrolytic kinetic resolution, esterification, ring-closing metathesis (RCM), and cross-metathesis (CM) reactions.     

Stereoselective total synthesis of simplactone A

The efficient and simple stereoselective approach toward the total synthesis of simplactone A is described. The key features of this synthetic strategy include stereoselective C-ethylation, selective triol protection, and Wittig olefination for the formation of the six-membered ring.     

Stereoselective one-pot three-component coupling approach towards the synthesis of the AC ring system of taxanes

The stereoselective one-pot three-component coupling reaction was accomplished by 1,4-addition of the protected cyanohydrin ether 9f to cyclohexenone 10g and subsequent addition of the resulting enolate to formaldehyde in high yield for the formation of the AC ring system of taxanes. We found that the bulky substituents at the 10-position in the A ring prevent the desired 1,4-addition. Similarly, the bulky trialkylsiloxy groups at the 4-position in the C ring prevent the 1,4-addition and electron-donating alkoxy groups at the same position induce the undesired retro-Michael reaction.     

Stereoselective total synthesis of cochliomycin A

A convergent and stereoselective synthesis of cochliomycin A, a 14-membered resorcyclic acid lactone, based on chiron approach is described. The key reactions involved olefin cross-metathesis and sodium hydride promoted one-pot intramolecular lactonization. l-Arabinose was used as a chiral pool material for the construction of the key fragment.