Carboxylic methyl esters

C-6 Pectic carboxyl, methyl ester, free acid... 

The bidentate formate ligand of OsH(K2-02CH)(CO)(P,Pr3)2 is converted into a monodentate group by carbonylation. Thus, the reaction of this compound with carbon monoxide gives 0sH K1-0C(0)H (C0)2(P Pr3)2. Similarly, the addition of a stoichiometric amount of trimethylphosphite yields 0sH k -0C(0)H (C0) P(OMe)3 (P Pr3)2, and the addition of a stoichiometric amount of ethyne di-carboxylic methyl ester leads to 0sH K1-0C(0)H (C0)(r 2-Me02CC=CC02Me) (P Pr3)2, which in solution partially dissociates the alkyne. As is shown in... 

Diazomethane gives with these compounds the easily hydrolyzed carboxyl methyl esters (78) ... 

Scheme 29 Cleavage of Phosphonate, Phosphonamidate, and Carboxylate Methyl Esters Using Lithium Propanethiolate 67 71 73 103 ...

The first evidence for the existence of the methylation of a prenylated peptidyl substrate was found in two jelly fungi, Tremella mesenterica and Tremella brasiliensis [30,31]. These peptide sequences are similar to the a-mating factor found in Saccharomyces cerevisiae, which is also prenylated at the C-terminus and contains an a-carboxyl methyl ester [32]. The gene product of the STEM in S. cerevisiae was found to be responsible for the methylation event for the a-factor-mating pheromone and the enzymatic activity of this methyltransferase was found only in the cellular membrane fractions [33,34]. Further analyses of Stel4p via epitope tagging determined that the enzyme is localized to the ER membrane and possesses six transmembrane segments, with majority of the enzyme exposed to the cytosol [35,36]. 

The four-step synthesis begins with the hydrogenation of PABA using Rh/AliOs to furnish a 92% yield of 77 as an 80 20 cisitrans mixture. Subsequent heating at 250°C in Dowtherm A to effect epimerization-cyclization afforded the bicyclic lactam (78) in 84% yield. Red-Al reduction furnished 2-azabicyclo[2.2.2]octane which was subsequently protected as the tosylate salt (79) in 85% yield. Employment of more concentrated Dowtherm mixtures and a decreased amount of Red-Al increased the yield for the cyclization step to 89% and the tosylate salt to 91% (overall yield 70%) [85]. Earlier, Werner [86] demonstrated that using the carboxylate methyl ester instead of the carboxylic acid allows the cyclization to occur at lower temperatures (190°C). 

The iodine-lithium exchange reaction of fcw(2,2,2-trifluoroethyl) iodomethylphosphonate with t-BuLi followed by a CO, quench gives fcw(2,2,2-trifluoroethyl) 1-(hydroxycarbonyl)metliyIphos-phonate, which cannot be obtained by hydrolysis of the carboxylic methyl ester." ... 

Palladium-catalyzed carbonylation of chloropyrazines in methanol and in amines yields the pyrazine carboxylic methyl esters and carboxamides, respectively. This procedure has been successfully applied to the synthesis of 2,5-pyrazinedicarboxylic acid derivatives and 3-methoxy-carbonylpyrazine 1-oxide from the corresponding dichloropyrazines and A-oxides <908923 >. 

Fig. 9.1. (A) Chromatogram of a ten

Perfluorocarboxylate polymers in the carboxylic methyl ester, potassium salt and carboxylic acid forms were analysed by FTIR transmission and ATR spectroscopies. Band assignments were made for most of the dominant peaks. An absorbance band ratio, comparing the 555/cm C-F band to the 982/cm C-O-C ether band, was found to be a direct measure of the equivalent weight of the polymers. In addition, the transition from the methyl ester form to the acid form was determined by examining the 2969/cm methyl ester band versus the broad 3200/cm band. Quantitative expressions were presented for use in the computation of equivalent weight and acid content based on the FTIR thin film absorbance measurements. The technique used provided a direct measure of the trade-off... 

The product of protein methylase II, carboxyl-methyl ester, undergoes rapid and spontaneous hydrolysis into methanol at physiological pH and temperature, and the proposed physiological role(s) of the reaction are mainly related to the neutralization of anionic charges of the protein, which may result in conformational changes. 

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