Table 3. Effectiveness of different coupling reagents^a.

entry	coupling reagentb, c	T/°C	time/h	% conversiond, e
1	triphosgene	45	0.5	94%
2	DIC/HOAt	45	0.5	34%
3	HATU/HOAt	45	0.5	11%
4	TFFH/HOAt	45	0.5	9%
5	PyBrOP/DMAP	45	0.5	trace
6	HBTU	25	12	trace
7	TBTU	25	12	trace
8	PyBOP	25	12	trace
9	amino acid chloridef	25	2	trace
10	DAST	25	2	trace

^aOptimization studies were performed with peptide 9 sequence; results of amide bond formation between an N-allylalanine residue and FmocGlu(tBu)-OH on Rink amide resin are shown.

^bWith microwave irradiation; see the experimental section for details.

^cDMF was used as a solvent with all coupling agents except for THF with triphosgene.

^dDetermined from analytical HPLC.

^eResults after three different treatments with the Fmoc amino acid and coupling agent.

^fPre-synthesized nosyl amino acid chloride.⁸