sumtnmy : Redution 06 dicvry1 dAuR,jideA with I-benzyt-l,4-dihydtronicofivmmide (ENAH] ptoceeded &tough a had-&at chain heation, wkiee di.a.tkyL dhu&du wem dound to be inat to BNAH. Thiols, such as glutathione, and redox enzymes whose active site possesses two cysteine residues in proximity, reduce phisiologically important substances in living organisms. 1) In this process the thiol group in these coenzymes and enzymes is converted to the corresponding oxidized disulfide which is then reduced back to the original thiol with NADPH by the aid of the corresponding disulfide reductases , such as glutathione reductase, thioredoxin reductase, tic. 2) Earlier, Wang ti &. reported, based on only the spectral change of the reaction mixture after one month at room temperature under nitrogen in the dark, that both diphenyl disulfide and lipoamide were successfully reduced to the corresponding thiols with BNAH, a model of NADPH, though they did not isolate the reduction products. 3) When we followed their experiment under the same conditions as Wang eX &. applied, no reaction between diphenyl disulfide and BNAH was found to take place. However, the reduction of diary1 disulfides with BNAH was found to proceed nicely in a radical chain process, when the reaction was initiated by a certain radical initiator or irradiation with visible light. This letter deals with this reaction of diary1 disulfides with BNAH. When a solution of p,p'-dichlorodiphenyl disulfide (&, 0.X r;miole) and BNAH (1.00 mmolc) was heated at 80ยฐC in 2 ml of solvent in a degassed sealed tube, p-chlorobenzenethiol was found to be formed upon HPLC analysis at the initial stage of the reaction. After all the disulfide was consumed, l-benzyl-6-(p-chlorophenylthio)-1,4,5,6-tetrahydronicotinamide (&)4) benzyl p-chlorophenyl sulfide and nicotinamide were isolated as the major products, however the thiol was not detected in the final product mixture. The initial step of the reaction between $ and BNAH would involve an electron transfer and may be expressed by ea.1, forming the intermediate (BNA+), which