Improved approach for anchoring Nα‐9‐fluorenylmethyloxycarbonylamino acids as p‐alkoxybenzyl esters in solid‐phase peptide synthesis

Several Fmoc‐amino acids have been esterified by use of N,N‐dimethylformamide dineopentyl acetal (2) to 2,4,5‐trichlorophenyl 3‘‐(4“‐hydroxymethyl‐phenoxy)propionate (7), and the resultant handle derivatives (5) were purified and then quantitatively coupled onto aminomethyl supports. Compared to literature methodology, the present procedure is preferred because: (i) extra steps to selectively protect and liberate the carboxyl of the handle are circumvented; and (ii) the additional methylene group spacer reflecting substitution of a propionyl group for an acetyl group in the handle changes the electronic parameters of the resultant p‐alkoxybenzyl ester sufficiently so that the rates of acidolytic cleavage of the anchoring linkage are 2‐ to 3‐fold increased and useful improvements in yields can be achieved.