Cesium alkanoates (chiefly the propionate) have been investigated for their solubility, nucleophilic reactivity, and degree of ion pairing in dimethylformamide (DMF) and, in some cases, dimethyl sulfoxide (DMSO) solutions.133Cs NMR has been used to establish the degree of ion pairing. From the data obtained it is concluded that the cesium ion is virtually completely solvated and that the carboxylates are essentially free and highly reactive. The consequences of this effect on macrocyclization by means of nucleophilic substitution are discussed.

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A glutathione S-transferase (GST) with activity toward 1,2-epoxy-2-methyl-3-butene (isoprene monoxide) andcis-1,2-dichloroepoxyethane was purified from the isoprene-utilizing bacterium Rhodococcus sp. strain AD45. The homodimeric enzyme (two subunits of 27 kDa each) catalyzed the glutathione (GSH)-dependent ring opening of various epoxides. At 5 mM GSH, the enzyme followed Michaelis-Menten kinetics for isoprene monoxide and cis-1,2-dichloroepoxyethane, withV max values of 66 and 2.4 μmol min−1 mg of protein−1 andKm values of 0.3 and 0.1 mM for isoprene monoxide and cis-1,2-dichloroepoxyethane, respectively. Activities increased linearly with the GSH concentration up to 25 mM.1H nuclear magnetic resonance spectroscopy showed that the product of GSH conjugation to isoprene monoxide was 1-hydroxy-2-glutathionyl-2-methyl-3-butene (HGMB). Thus, nucleophilic attack of GSH occurred on the tertiary carbon atom of the epoxide ring. HGMB was further converted by an NAD+-dependent dehydrogenase, and this enzyme was also purified from isoprene-grown cells. The homodimeric enzyme (two subunits of 25 kDa each) showed a high activity for HGMB, whereas simple primary and secondary alcohols were not oxidized. The enzyme catalyzed the sequential oxidation of the alcohol function to the corresponding aldehyde and carboxylic acid and followed Michaelis-Menten kinetics with respect to NAD+ and HGMB. The results suggest that the initial steps in isoprene metabolism are a monooxygenase-catalyzed conversion to isoprene monoxide, a GST-catalyzed conjugation to HGMB, and a dehydrogenase-catalyzed two-step oxidation to 2-glutathionyl-2-methyl-3-butenoic acid.

ether gave pure la (30 mg, 15%): mp 188-189 "C; NMR7 (acetone-d6 + DzO) d 3.04 (s, 3, CH3), 4.38 (d of q, 1, H3), 4.78 (d, 1, H4), 6.08 (d of d, 1, Hz), 7.25-8.25 (m, 7, H1 and aromatic), 8.73 trans-3,4-Dihydroxy-anti-1,2-epoxy-1,2,3,4-tetrahydro-7methylbenz[a]anthracene (2). A solution of la (23 mg, 0.083 mmol) and rn-chloroperbenzoic acid (230 mg) in 25 mL of dry THF was stirred under Nz for 2 h at room temperature. The solution was diluted with ether, washed twice with 10% aqueous NaOH solution and water, and dried. Evaporation of the solvent (avoiding heating), followed by trituration with ether, gave 2 (13 mg, 57%) as a white solid: mp 183-185 "C; NMR ( a~e t 0 n e -d~ 4.88 (d, 1, H4), 5.40 (d, 1, H1), 7.38-8.41 (m, 6, aromatic), 8.85 (s, trans -1,2-Dihydroxy-an ti -3,4-epoxy-1,2,3,4-tetrahydro-7methylbenz[a]anthraoene (4a). Epoxidation of 3a (23 mg, 0.08 mmol) was carried out by the procedure employed for the analogous reactions of la. Evaporation of the solvent (avoiding heating) gave crude 4a (20 mg, 74%) which showed one major peak (80%) on LC on a Ihpont Si1 column (THF-heptane, 4555). The major peak was collected and identified as 3a: NMR (acetone-d6 + The reactions of 1,2,6-trimethyl-3,5-bis(methoxycarbonyl)-l,4-dihydropyridine (2a), l-methyl-3,5-bis(methoxycarbonyl 1-1,4-dihydropyridine (2b), and l-benzyl-3-acetamido-1,4-dihydropyridine (1) with various sulfonium salts have been investigated. On thermal (60 "C) activation 2a,b react with, for example, methylphenacylphenylsulfonium tetrafluoroborate (3b) to give the respective pyridinium salts, acetophenone, and phenyl methyl sulfide. There is some competing isomerization of the 1,4-dihydropyridines to their (nonreactive) 1,2-dihydro isomers, this being catalyzed by the pyridinium salt formed on reduction of the sulfonium salt. Phenacyl-, acetonyl-, and in some cases benzylsulfonium salts can be reduced. The group to which hydride transfer takes place should be electron deficient. These reductions can be initiated at rwm temperature with visible light (at rmm temperature pyridinium :salt induced isomerization of the 1,4-dihydropyridine to its 1,2 isomer occurs only over a period of several days:i. The effect of visible light can be enhanced greatly by adding small amounts of dyes to the reaction mixtures. Eosin sodium salt, tetraphenylporphine, and R~"(2,2'-bpy)~Cl~ are all capable of increasing the rate of reduction; the last dye is by far the most effective. The results of mechanistic investigations are consistent with the hypothesis that the light-induced reductions are one-electron transfer reactions. In some cases there appears to be a separate thermal mechanism not sensitive to either light or sensitizers. Some sulfonium salts react with dihydropyridines to give the pyridinium salt and sulfide in less than quantitative yield and no reduction products from the sulfonium salt. As determined for the case of the reaction of bromomalonitrile with 1, and presumably also for other reactions, alkylation of an enamine carbon in the dihydropyridine is ...