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<i>S</i>-Thyminyl-<i>L</i>-cysteine methyl ester hydrochloride (compound 1), a non-classical peptide nucleic acid monomer, was synthesized through the key intermediate, <i>N-tert</i>- butoxycarbonyl-<i>S</i>-thyminyl-<i>L</i>-cysteine (compound 3), which afforded from the reaction of <i>S</i>-thyminyl-<i>L</i>-cysteine hydrochloride (compound 2) with di-<i>tert</i>-butyl dicarbonate (Boc₂O). This was followed by the esterification and deprotection of compound 3 at an overall yield of 82%. The mixture of thionyl chloride and methanol was found as an efficient reagent for simultaneous deprotection of <i>tert</i>-butoxycarbonyl (Boc) group and esterification of carboxy group of compound 3. This high-yield two-step method was also applied to other analogues of compound 1 successfully. The chemical structures of four new compounds (5a-5d) were confirmed by ¹H NMR and ¹³C NMR.DOI: http://dx.doi.org/10.4314/bcse.v26i3.10