Asymmetric Synthesis of the Aromatic Fragment of Sespendole

Sespendole is an indole sesquiterpene alkaloid bearing two isoprenyl groups, one of which is highly oxidized. Herein, we disclose an eight-step synthesis of the aromatic fragment of sespendole in an optically pure form, starting from 4-bromo-2-fluoronitrobenzene. The key steps were a Claisen rearrangement at room temperature for introduction of the prenyl group and a coupling between the dianion generated from prenylated bromo-N-tosylanilide and a chiral epoxy aldehyde.

13-Demethyl-13-substituted-13,14-dihydroretinols as potential affinity labels of retinol-binding proteins: syntheses and stability studies

13-Demethyl-13-substituted-13,14-dihydroretinols were synthesized and their stability under various conditions was measured in order to evaluate whether they would be useful as affinity labels of retinol binding proteins and retinol metabolizing enzymes. The 13-chloro analog could not be isolated because it eliminated HCl under the Wittig reaction conditions of its preparation. The trans- and cis-13,14-epoxy analogs are stable in non-protic organic solvents, but undergo an elimination reaction under various chromatographic conditions and in mixtures of organic solvents with water or alcohol. The 13-hydroxy and 13-methoxy analogs are stable in aqueous solutions and are therefore suitable for biological studies.

A facile synthesis of enantiopure 2-aziridinesulfinimines and their highly diastereoselective reactions with phosphite anions

Two novel enantiopure 1-benzyl-2-aziridinesulfinimines bearing a chiral group on both sides of the carbon-nitrogen double bond were synthesized from the condensation of racemic 1-benzyl-2-aziridinecarboxaldehyde and enantiopure p-toluenesulfinamide. The addition reaction with phosphite anion followed by the ring-opening reaction with thiophenol provided chiral alpha,beta-diamino-phosphonic acid derivatives. The addition reactions showed the operation of a double-stereodifferentiation effect. The possible transition states of the reaction were proposed, and high diastereoselectivities of the addition reactions of phosphite anions to both aziridinesulfinimines were realized in the presence or absence of zinc bromide.

Diastereoselective formation of cyanohydrins from alpha-alkoxy aldehydes

[reaction: see text] The reaction of alpha-alkoxy aldehydes with Et4NAg(CN)2 or Me3SiCN in the presence of MgBr2 x OEt2 in CH2Cl2 at 0 degrees C gives the corresponding syn cyanohydrins in good yield with high diastereoselectivity. Excess MgBr2 x OEt2 (typically 5 equiv) is required for high diastereoselectivity. Et4NAg(CN)2 (but not Me3SiCN) is sufficiently reactive to give cyanohydrins at -78 degrees C, and higher diastereoselectivity is obtained at this temperature.