Exploration of Drug Science

Table 3

Scope of the C-terminal amino acids in conversion to amides

Entry	Xaa	Product	HPLC purity (%)^a
			Ammonolysis			Staudinger reaction
			4	2	8	4	2
1	Gly	2a	86	5	6	94	6
2	Ala	2b	80	4	9	84	7
3	Val	2c	82	2	8	91	1
4	Ile	2d	91	< 1	< 1	92	< 1
5	Leu	2e	74	5	13	94	4
6	Phe	2f	87	6	< 1	91	6
7	Pro	2g	90	1	4	86	2
8	Ser	2h	79	3	9	93	4
9	Thr	2i	71	3	13	91	3
10	Glu	2j	< 1	77	< 1	4 (74)^b	87
11	Cys	2k	39^c	< 1	< 1	26	7
12	Cys(Acm)	2k’	75	9	10	93	< 1
13	Met	2l	80	6	9	87	4
14	Tyr	2m	83	8	2	85	5
15	His	2n	45	39	4	68 (83)^b	28
16	Lys	2o	86	5	6	87	6
17	Arg	2p	91	6	< 1	91	5
18	Trp	2q	82	8	< 1	80	8

^a detected at 220 nm; ^b azidation was performed in TFA solution instead of acidic aqueous condition; ^c disulfide dimer of 2k was observed