A convenient and highly efficient synthesis of one kind of peptide nucleic acid monomer

S-Thyminyl-L-cysteine methyl ester hydrochloride (compound 1), a non-classical peptide nucleic acid monomer, was synthesized through the key intermediate, N-tert- butoxycarbonyl-S-thyminyl-L-cysteine (compound 3), which afforded from the reaction of S-thyminyl-L-cysteine hydrochloride (compound 2) with di-tert-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 tert-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