Cedric W. Holzapfel

The Chiral Synthesis of Thiazole Amino Acid Enantiomers

Abstract An efficient modified Hantzsch reaction is described for the synthesis of optically pure thiazole amino acid derivatives from the corresponding amino acids. The method is exemplified by the synthesis of a derivative of L-(Gln)Thz, the novel chiral thiazole amino acid moiety of dolastatin 3. The Cotton effects of thiazole amino acids correlate well with the absolute stereochemistry of these compounds.

Palladium-catalysed substitution reactions of geminal allylic diacetates

Abstract The Pd(0)-catalysed substitution of allylic 1,1-diacetates by both carbon and oxygen nucleophiles is described. The products isolated resulted from either single or double substitution reactions.

The isolation and structure of a toxic metabolite from Diplodia maydis (Berk.) Sacc.

Abstract Diplodiatoxin is a toxic metabolite of Diplodia maydis (Berk.) Sacc. Studies are described which have led to the structure as shown in 1a.

A Simple Cycloaddition Approach to a Racemate of the Natural Sweetener Monatin

Abstract The reaction of methyl 2-(3-indolylmethyl)-acrylate 2 with carbethoxyformonitrile oxide 3, followed by saponification and reduction, gives mainly racemic monatin 1. Preliminary attempts to adapt the 2+3 cycloaddition to a new chiral synthesis of monatin, is described.

STEREOSELECTIVE SMI2-MEDIATED CONVERSION OF CARBOHYDRATES INTO CYCLOPENTANOLS

Carbohydrate derivatives were employed as precursors in the synthesis of stereodefined cyclopentanols. This rapid conversion was effected by a zinc-assisted Grob-fragmentation, followed by a stereocontrolled SmI2-mediated cyclisation.

ONE-POT SMI2-PROMOTED TRANSFORMATION OF CARBOHYDRATE DERIVATIVES INTO CYCLOPENTANOLS

Abstract Selectively functionalised carbohydrate derivatives underwent SmI 2 -promoted Grob-fragmentation reactions. This was followed by an in situ , stereocontrolled SmI 2 -mediated cyclisation to afford the corresponding cyclopentanols.

A facile route to 3a,8a-dihydrofuro[2,3-b]benzofurans

Abstract Consecutive employment of palladium-catalysis and samanum(II)iodide-induced radical chemistry allows access to analogues of the ABC enol ether tricycle of aflatoxin B 1 ( 1 ). The Pd-assisted coupling of tubutylstannyl ethers of various 2-iodophenols with 2,5-diacetoxy-2,5-dihydrofuran ( 4 ) provided products that could be cyclised into 3a,8a-dihydrofuro [2,3- b ]benzofurans using SmI 2 . Elimination of an acetatosamarium species provides the requisite unsaturation situ .

The biosynthesis of the ochratoxins, metabolites of aspergillus ochraceus

Abstract The biosynthesis of ochratoxin A (Ia) was studied in Aspergillus ochraceus Wilh. by experiments in which dl -phenylalanine [U- 14 C], sodium acetate [1- 14 C] and methionine [ 14 CH 3 ] were supplied to a resting culture of the fungus. The carboxyl carbon of the amide group is shown to be derived from the C 1 -pool.

The nitration of electron-rich aromatics

Abstract The successful mononitration of a variety of electron-rich aromatic substrates is reported, employing either nitronium tetrafluoroborate or “claycop” as the nitrating agent. Dinitration of four of the substrates was achieved when employing nitronium tetrafluoroborate. Several of the products have previously been prepared only by indirect methods.

The Synthesis of a γ-Keto-α-amino Acid, a Key Intermediate in the Synthesis of Monatin, a New Natural Sweetener

Abstract An efficient method was developed for the synthesis of the ketoamino acid 2, a key intermediate in the synthesis of the novel sweet compound, monatin 1. Preparation of 2 entails coupling of a suitably protected indole acetate anion to an aspartic acid derivative.