Esters Diazomethane-Alumina

The methyl ester (100, R = CH3), derived from this A-nor acid by treatment with diazomethane, is different from the ester (102) obtained either by Favorskii rearrangement of 2a-bromo-5a-cholestan-3-one (101) or by the action of cyanogen azide on 3-methoxy-5a-cholest-2-ene (103) followed by hydrolysis on alumina. The ketene intermediate involved in photolysis of (99) is expected to be hydrated from the less hindered a-side of the molecule to give the 2j -carboxylic acid. The reactions which afford (102) would be expected to afford the 2a-epimer. These configurational assignments are confirmed by deuteriochloroform-benzene solvent shifts in the NMR spectra of esters (100) and (102). ... 

Other important porphyrins which can be derived from hemin are hematoporphyrin (5) and mesoporphyrin (6). Hematoporphyrin (5) which is commercially available at a relatively low price is sensitive towards acid due to the 1-hydroxyethyl groups, so commercial samples contain only 60 to 70% of hematoporphyrin. Pure hematoporphyrin dimethyl ester which is a racemic and diastereomeric mixture of four stereoisomers can be obtained by esterification with diazomethane and subsequent chromatography on neutral alumina.84 The pure stereoisomers can be prepared by enantioselective reduction of diacetyldeuteroporphyrin dimethyl ester.85a b The... 

Monoesterification of dicarboxylic acids. Chemiabsorption of a dicarboxylic acid on alumina or silica can be used to effect selective esterification of one acid group with diazomethane. The method was demonstrated by conversion of terephthalic acid, C6H4-l,4-(COOH)2) into the monomethyl ester in quantitative yield. 

Mono esters of dicarboxylic acids.1 Aliphatic straight-chain dicarboxylic acids when adsorbed on alumina react with diazomethane to form monomethyl esters in quantitative yield. Terephthalic acid, isophthalic acid, and 1,4-cyclohexanedi-carboxylic acid are also converted selectively to the monomethyl esters. However, phthalic acid does not show any enhanced selectivity under these conditions. Evidently selectivity for monoesterification results from adsorption of one of the acid groups on alumina. 

Urine. Urine samples collected from cows 821 and 59 in the 0-12 hour period after the administration of a 30 mg dose (injection 2) were utilized in the isolation and identification of metabolites. The isolation procedure involved ethyl acetate extraction of urine followed by solid phase extraction of the ethyl acetate extract on C-18 Bond Elut cartridges. The extract was derivatized into methyl esters with diazomethane and subjected to silica and alumina chromatography for further cleanup prior to analysis. The detailed procedure is described in flow diagram 1. 

Selective monomethylation of dicarboxylic acids has been reported using A/ /wi a as an additive (eq 9) " It is thought that one of the two carboxylic acid groups is bound to the surface of the alumina and is therefore not available for reaction. Carboxylic acids that are engaged as lactols will also undergo methylation with diazomethane to provide the methyl ester and aldehyde (eq 10). ... 

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