Acetic acid, labeled with methyl ester

This route is especially convenient because no over-alkylation of the anion of acetonitrile occurs. Over-alkylation can be a problem in attempts to methylate the anion of diethyl cyano-methylphosphonate (4) directly a mixture of unalkylated, monoalkylated and dialkylated products in a ratio of 1 2 1 is formed. The same problem arises with the alkylation of triethyl phosphonoacetate (11). For the preparation of a Ca-ester synthon, an alternative method to the propionitrile route is used (Scheme 7). This method has been used in the synthesis of labelled Cio-central units, described in the next Section. The starting material is acetic acid (9) which is converted into ethyl bromoacetate (10) as described above (Scheme 3). The ethyl bromoacetate (10) is reacted with triphenyl phosphine in a nucleophilic substitution reaction the phosphonium salt is formed (yield 97%). The phosphonium salt is deprotonated in a two-layer system of dichloromethane and an aqueous solution of NaOH. After isolation, the phosphorane 22 is reacted at room temperature with one equivalent of methyl iodide (19) the product consists mainly of the monomethylated phosphonium salt (>90%) which is deprotonated with NaOH, to give the phosphorane 23 in quantitative yield relative to phosphorane 22, and 23 is reacted with the aldehyde in dichloromethane. The ester product 12 can subsequently be reduced to the corresponding alcohol and reoxidized to the aldehyde 8. An alternative two-step sequence for this has also been used. First, the ester 12 is converted into the A -methyl-iV-methoxyamide (16) quantitatively by allowing it to react with the anion of A, 0-dimethylhydroxylamine as described above (Scheme 5). This amide 16 is converted, in one step, into the aldehyde 8 by reacting it with DIB AH in THF at -40°C [46]. 

CoASH for 15 minutes. Labeled microsomes were separated into equal aliquots for assays. Assay reactions contained ImM reduced dinucleotide and were allowed to proceed 1-3 h prior to terminating by extracting with 2 vol chloroform methanol (2 1) and addition of a few drops of 1 M oxalic acid. Chlorofom extracts were blown to dryness with N2 and lipids were methylated by first adding 0.5 ml sodium methoxide (18 mg/ml) in methanol for 30 min and then adding ethereal diazomethane. In order to ensure complete recovery of lipids, methyl esters were extracted with 2 vol of chloroform water was added for phase separation. Chloroform extracts were concentrated to a volume of 50 pi for analysis on silica gel TLC in hexane diethyl ether acetic acid (85 15 1). 

Illuminated Amaranthus chloroplasts synthesized fatty acids from [1- C]acetate (17,5 mmol/Ci) at constant rates (800-2,200 nmol acetate h Vmg chlorophyll) for at least 5 min, and the label was incorporated into free fatty acids, PA, DG, lyso-PA and acyl-ACP, The labeled acyl-ACPs were recovered from the chloroplasts by a precipitation method modified from that of Mancha et al. (1975) The incubation was stopped by adding 1 volume of 5% acetic acid/2-propanol, and acyl-ACPs were precipitated by successive additions of 25 yl of saturated (NH )2S0 and 5 ml of CHCl /CH OH (2 1,v/v) containing 1% (v/v) of acetic acid. Radioactivity of the acyl-ACPs, which was counted after their acyl groups were converted to methyl esters by treatment with NaOCH, reached the saturation level within 1 min, and the level remained almost constant until the rate of fatty acid synthesis began to fall off after 5-min incubation or more. When the rate of fatty acid synthesis was at 2,200 nmol acetate h Vmg chlorophyll after 5-min incubation, [18 1-ACP], [18 0-ACP] and [16 0-ACP] were calculated to be 44, 99 and 71 pmol/mg chlorophyll, respectively. 

Methyl 8-oxooctanoate-4,5-D2, 35, and methyl 12-oxododecarbate-4,5,8,9-D4, 36, have been synthesized32 as shown in equations 13 and 14 by monoozonization and sodium acetate cleavage of 1,5-cyclooctadiene and 1,5,9-cyclododecatriene, respectively. The resultant unsaturated aldehydic acids 37 and 38 have been converted to the corresponding acetal esters, which have been deuteriated with Wilkinson s catalyst33 and hydrolysed to the deuterium-labelled aldehydic esters 35 and 36 in 47% and 49% overall yields and... 

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