James L. Charlton

Synthesis, isolation, and characterization of conjugates of ovalbumin with monomethoxypolyethylene glycol using cyanuric chloride as the coupling agent

The experimental conditions for the preparation of conjugates of ovalbumin (OA) and monomethoxypolyethylene glycol (mPEG) of a preselected average degree of conjugation, n, using cyanuric chloride as the coupling agent, have been investigated with emphasis on purification and characterization of the products. These conjugates served as prototypes of tolerogenic mPEG derivatives of antigenic proteins which were capable of suppressing in mammals the immunological response to the corresponding unmodified antigens. In other studies in this laboratory, the tolerogenicity of OA(mPEG)n conjugates was found to be a function of n. The reproducibility of the reaction leading to the production of OA(mPEG)n conjugates was shown to depend primarily on the reactivity of the mPEG-cyanuric chloride intermediate, which--for best results--had to be synthesized under completely anhydrous conditions. Isolation of the OA(mPEG)n conjugates was optimized by the use of ion-exchange chromatography whereby rapid removal of large amounts of uncoupled intermediate from the conjugate was achieved; the conditions of fractionation were affected by the degree of conjugation. This method of purification was superior to dialysis, ultrafiltration, and gel filtration. Furthermore, by the application of analytical hydrophobic interaction HPLC it was possible to differentiate among conjugates of different degrees of conjugation and to establish the absence of any detectable free OA in any of the preparations. The quantity of mPEG in the conjugates was determined directly by NMR.

Thermal generation of alpha-hydroxy-orthoquinodimethane and reaction with the fumarate, maleate and acrylate of S-methyl lactate

Abstract The thermal generation and reaction of α-hydroxy-o-quinodimethane with the furmarate, maleate and acrylate of S-methyl lactate is described.

Thomasidioic acid and 6-hydroxy-5,7-dimethoxy-2-naphthoic acid: Are they really natural products?

Abstract It has been shown that air oxidation of alkaline aqueous solutions of sinapic acid produces both thomasidioic acid ( 1 ), and 6-hydroxy-5,7-dimethoxy-2-naphthoic acid ( 2 ) in high yield, with the relative amounts dependent on the basicity of the solution. It has also been shown that naphthoic acid 2 is a secondary oxidation product of thomasidioic acid, a reaction that also produces 2,6-dimethoxy- p -benzoquione ( 3 ). The question of whether compounds 1, 2 and 3 are really natural products, as previously reported, is discussed.

Phase Transfer Catalysed Synthesis of Methyl α-Bromomethylacrylate

Abstract Methyl α-bromomethylacrylate 1 is an important intermediate both as a starting material for specifically functionalized polymers and for use in general organic synthesis. As an example of the former it has been used to prepare polymeric anthraquinoid dyes1. Synthetically, its bifunctional reactivity towards nucleophilic attack has made it useful in the preparation of both spiro2 and bicyclic3,4 ring systems. Several reports of synthetic methods leading to α-methylenelactones, having potential antitumor activity, have also been reported which use α-bromomethylacrylate as a starting point5.

Chemically induced dynamic nuclear polarization at zero magnetic field

Abstract A simple method is developed for calculation of nuclear polarization in products of radical coupling reactions carried out at zero magnetic field.

Conversion of phenolics to lignans: Sinapic acid to thomasidioic acid

Changes in sinapic acid when exposed to aqueous alkaline conditions were elucidated. Sinapic acid was exposed to a volatile buffer (pH 8.5) for 24 h, lyophilized, acidified, extracted, and characterized using nuclear magnetic resonance and mass spectroscopy. The product obtained was identified as the lignan thomasidioic acid. This identification was confirmed by comparison with a synthesized authentic sample of thomasidioic acid. Conversion of sinapic acid to thomasidioic acid under alkaline conditions previously has not been reported. Thomasidioic acid was present after exposure of sinapic acid to pH 8.5 for as few as 6 h. Thomasidioic acid also was formed at pH 7.

An asymmetric Diels-Alder cycloaddition to alpha-hydroxy-alpha-phenyl-orthoquinodimethane

Abstract The cycloaddition of the fumarate of methyl (R)-mandelate to α-hydroxy-α-phenyl- o -quinodimethane 3 gives a single diastereomer in high yield. The absolute stereochemistry of the cyctoadduct is established and the potential of the reaction for asymmetric lignan synthesis is discussed.

Asymmetric induction in Diels-Alder reactions of o-quinodimethanes

Abstract Asymmetric inductive effects have been measured on the Diels-Alder reaction of dimethyl fumarate with o-quinodimethane bearing a chiral α-alkoxy group. The chiral substituents used were 1-phenylethoxy, 2-(1-phenyl)propoxy, 1-(2-phenyl)propoxy, 2-(4-phenyl)-butoxy and 1-cyclohexylethoxy. The greatest asymmetric induction was found with the first of these chiral substituents (47% ee). A π-stacking effect, previously suggested as the rationale for asymmetric induction in a similar system, is shown to be inconsistent with the results from this study.

Synthesis of chiral esters of acetylenedicarboxylic acid

A general method for the preparation of acetylenedicarboxylic acid esters has been investigated and several esters have been prepared in excellent yield. The bis-(methyl (S)-lactyl), bis-(methyl (R)-mandelyl), and bis-menthyl esters were prepared, as well as achiral diaryl and dialkyl esters. The esters were synthesized from the corresponding dibromofumarates by 2,3-dibromo elimination using zinc or zinc amalgam in THF at room temperature or at reflux. The dibromofumarates were prepared by the esterification of dibromofumaryl chloride with the corresponding alcohols.

Lactate as chiral auxiliary in asymmetric photodeconjugation of unsaturated esters

Abstract The asymmetric photodeconjugation of the α,β-unsaturated esters 1 , 2 and 3 , to the, corresponding β,γ-unsaturated esters having a new chiral center at the α position, has been studied in a variety of solvents. In most solvents, the (S)-lactyl chirnal auxiliary induced the S configuration at the new chiral center. However, irradation of 1 in methanol or 2-propanol/water mixtures gave an unusual reversal of diastereoselectivity to produce the R configuration at the new chiral center.