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(2R, 5S) - (+) -cis-3, 5-Dimethyl-2- (3-pyridyl) thiazolidin-4-one hydrochloride (SM 12502), a new PAF antagonist, was labeled with carbon-14 at C 2 of the thiazolidinone ring for use in metabolic studies. The synthesis was achieved according to the scheme illustrated in Fig, 3. 14C-Carbonation of 3-pyridyllithium (3) followed by chlorination and esterification gave mehyl [carbonyl-14C] nicotinate (6) . Reduction of 6 with diisobutylaluminium hydride produced a mixture of the alcohol (7) and the aldehyde (8) . Oxidation of the mixture with manganese dioxide gave 8 as a sole product. Condensation of 8 with methylamine and subsequent cyclocondensation of the imine (9) with (S) -2-mercaptopropionic acid (10) yielded a cis and trans mixture of the thiazolidinone (11) . Isolation of the desired stereoisomer by chiralphase HPLC and subsequent treatment with hydrochloric acid afforded 1. The overall yield of 1 was 22% from 2.

Two stereoisomers of empenthrin, (E) -1-ethynyl-2-methyl-2-pentenyl (1 R) -cis, trans-chrysanthemates, were regioselectively labeled with carbon-14 for use in metabolic studies on the characteristic ethynyl alcohol moiety. Action of ethyl [14C] formate (2) on ethylidenetri-phenylphosphorane gave the 14C-formylated phosphorane (3) . Wittig reaction of 3 with propanal stereoselectively yielded the E isomer of 2-methyl-2- [1-14C] pentenal (4), which was derivatized to a crystalline imidazolidine (5) for purification. Regeneration of 4 from purified 5 followed by reaction with ethynylmagensium bromide gave (E) -1-ethynyl-2-methyl-2- [1-14C] -pentenol (6), the a-ethynyl alcohol of 14C-labeled empenthrin, in 36% overall radiochemical yield from 2. Esterification of 6 with (1R) -cis- and (1R) -traps-chrysanthemoyl chlorides afforded the corresponding optically active [pentenyl-1-14C] empenthrins (1a and 1b) in good yields after chromatographic purification.

Farnesylacetic acid was efficiently labelled with 14C at the 5-position and gefarnate, a potent ulcer inhibitor, was prepared from it in radioactive form for use in metabolic studies. Condensation of [carbonyl-14C]acetyl chloride (5) with t-butyl 2-ethoxymagnesiomalonate (6) followed by acid-catalyzed deprotection and decarboxylation gave ethyl 3-oxo[3-14C]butanoate (8). Alkylation of the keto ester (8) with geranyl bromide (9) afforded the unsaturated keto ester (10), which was hydrolyzed and decarboxylated to give geranyl[2-14C]acetone (11). Grignard reaction of 11 with cyclopropylmagnesium bromide followed by treatment with hydrobromic acid yielded [4-14C]homofarnesyl bromide (13). Cyanation of 13 with potassium cyanide and subsequent hydrolysis gave [5-14C]farnesylacetic acid (1) in 6.1% yield from barium [14C]carbonate (3). Chlorination of 1 followed by esterification with geraniol afforded [5-14C]gefarnate (2) in 88% yield.

Bromobutide, a novel herbicide, was labeled with carbon-14 independently at the carbonyl group and the phenyl ring for use in metabolic studies. 14C-Carbonation of neopentylmagnesium chloride (3) gave 3,3-dimethyl[1-14C]butyric acid (4a) quantitatively. Chlorination of 4a with thionyl chloride followed by alpha-bromination with bromine yielded 2-bromo-3,3-dimethyl[1-14C]-butyryl halide (5a), which was subsequently condensed with alpha, alpha-dimethylbenzylamine (6a) to afford [carbonyl-14C]bromobutide (1a). The overall yield of 1a was 76% from barium [14C]-carbonate (2). Similarly, condensation of alpha, alpha-dimethyl[phenyl-14C]benzylamine (6b), which was prepared from alpha-methyl[phenyl-U-14C]styrene (7) in three steps, with 2-bromo-3,3-dimethylbutyryl halide (5b) gave [phenyl-14C]bromobutide (1b) in 67% yield after purification. The specific activities of 1a and 1b were 1.38 and 0.781 GBq/mmol (37.2 and 21.1 mCi/mmol), respectively.