Synthesis of a peptide nucleic acid with a novel 1‐methyl‐6‐mercaptopurine base

A novel peptide nucleic acid (PNA) monomer 16 containing a novel 1‐methyl‐6‐mercaptopurine base was synthesized by coupling the in situ generated acid chloride of (1‐methyl‐6‐mercaptopurin‐9‐yl)acetic acid ( 6 ) into an L‐lysine backbone ( 13 ) using 10% CCl 4 in pyridine and Ph 3 P. Compound 6 was synthesized from 6‐mercapto‐1‐methylpurine and ethylbromoacetate in the presence of NaH followed by alkaline hydrolysis and subsequent neutralization with a cation exchange resin. The L‐lysine backbone ( 13 ) was obtained by the reaction of Nϵ‐CBZ‐L‐lysine allyl ester with Boc‐aminoactaldehyde in the presence of NaBH 3 CN under reductive amination conditions. Oligomerization of the monomer 16 to PNA analogues was achieved using BOC‐BHA‐PEG‐PS resin as a solid support and the in situ generated acid chloride of 16 by 10% CCl 4 in DCM in the presence of Ph 3 P.