A photochemical organocatalytic strategy for the direct enantioselective β-benzylation of α,β-unsaturated aldehydes is reported. The chemistry capitalizes upon the light-triggered enolization of 2-alkyl-benzophenones to afford hydroxy-o-quinodinomethanes. These fleeting intermediates are stereoselectively intercepted by chiral iminium ions, transiently formed upon condensation of a secondary am...

Stereoselective synthesis of variably protected α- and β-l-Ara4N glycosyl H-phosphonates as key intermediates in the syntheses of β-l-Ara4N-modified LPS structures and α-l-Ara4N-containing biosynthetic precursors is reported. A facile one-pot approach toward β-l-Ara4N glycosyl H-phosphonates includes anomeric deallylation of protected 4-azido β-l-Ara4N via terminal olefin isomerization followed...

The L-arginine acts stereoselectively on the Pc1.LSU nuclear group I intron of Pneumocystis carinii, competitively inhibiting the first step of the splicing reaction and stimulating the second step. A number of arginine-related compounds are more potent than L-arginine as stimulators and inhibitors. The most potent peptides tested are 10,000 times as effective as L-arginine in inhibiting ribozy...

Two hundred thirteen cytochrome P450 (P450) genes were collected from bacteria and expressed based on an Escherichia coli expression system to test their hydroxylation ability to testosterone. Twenty-four P450s stereoselectively monohydroxylated testosterone at the 2alpha-, 2beta-, 6beta-, 7beta-, 11beta-, 12beta-, 15beta-, 16alpha-, and 17-positions (17-hydroxylation yields 17-ketoproduct). Th...

Benzoyl radicals are generated directly from (hetero)aromatic aldehydes upon tetrabutylammonium decatungstate ((n-Bu(4)N)(4)W(10)O(32)), TBADT) photocatalysis under mild conditions. In the presence of alpha,beta-unsaturated esters, ketones and nitriles radical conjugate addition ensues and gives the corresponding beta-functionalized aryl alkyl ketones in moderate to good yields (stereoselective...

Highly efficient stereoselective 1,4-addition of racemic -fluoronitro(phenylsulfonyl)methane (FNSM) as a fluoromethyl pronucleophile to , -unsaturated ketones using a wide range of chiral organobifunctional catalysts under moderate conditions in the absence of an additional base has been achieved. A series of catalysts was screened for the enantioselective addition of FNSM to chalcones and the ...

A detailed study on the lithiation-electrophilic trapping of N-sulfonyl ethylene aziridines is described. The optimum results required use of a N-2,4,6-tri-iso-propylbenzenesulfonyl activating group and lithiation using 3 equiv. of s-BuLi-PMDETA for 1 minute before addition of the electrophile. In situ trapping with Me3SiCl was also successful. Electrophilic trapping with aldehydes provided a s...

The benzyl-protected disaccharide building blocks of core 8 O-glycan (15a/15b) for glycopeptide were stereoselectively synthesized by two glycosidation reactions with the glycosyl fluoride method. The building blocks were utilized in the solid-phase synthesis of a glycopeptide carrying two O-glycans with the consensus sequence of the tandem-repeat domain of MUC5AC. The synthetic glycopeptide wa...

PKSE biosynthesizes an enediyne core precursor from decarboxylative condensation of eight malonyl-CoAs. The KR domain of PKSE is responsible for iterative β-ketoreduction in each round of polyketide chain elongation. KRs from selected PKSEs were investigated in vitro with β-ketoacyl-SNACs as substrate mimics. Each of the KRs reduced the β-ketoacyl-SNACs stereoselectively, all affording the corr...

The peculiar versatility of remotely enolizable 6-methyluracil-5-carbaldehydes as useful vinylogous pronucleophiles in direct, asymmetric [4+2] cyclizations with suitable nitroolefins has been demonstrated. Under the strategic exploitation noncovalent bifunctional organocatalysis, a dearomative remote enolization strategy was implemented, to generate oQDM-type dienolate intermediates that were ...