. Author manuscript; available in PMC: 2009 Sep 15.

Published in final edited form as: Bioconjug Chem. 2006 Nov–Dec;17(6):1545–1550. doi: 10.1021/bc060154p

Table 1.

Optimization of N-TFA Cleavage Using Resin 34^a


			yields (%)^b
entry	conditions	time (min)	35	36	impurity^c
1	10% piperidine, 10% H₂O in DMF	30	0	100	0
2	0.6 M potassium silanolate in THF	30	0	100	0
3	15% N₂H₄ in DMF	75	9	91	0
4	15% N₂H₄ in DMF	180	34	64	2
5	15% N₂H₄, 15% MeOH in THF	300	100	0	0
6	15% N₂H₄, 15% MeOH in THF	180	99	>1	0
7	15% N₂H₄, 15% MeOH in THF	75	78	22	0
8	15% N₂H₄, 15% MeOH in THF	10	15	85	0
9	3% N₂H₄, 15% MeOH in THF	75	3	97	0
10	15% 0.5 M LiOH, 15% MeOH in THF	180	49	0	51
11	15% 0.5 M CsOH, 15% MeOH in THF	180	40	0	60

NDP-α-MSH Rink resin 34 (30 μL of resin slurry in THF) was placed into a small fritted 2 mL syringe and washed with an N-TFA cleavage solvent mixture. After the treatment, the resin was washed with THF and CH₂Cl₂, and the peptide was cleaved off the resin and side-chain protecting groups removed as described in the Materials and Methods section. The peptide was then dissolved in 30% aqueous MeCN and analyzed by HPLC using a linear MeCN/0.1% CF₃CO₂H aqueous gradient (10% to 40% in 30 min) at a flow rate of 1.0 mL/min.

Yields were determined as ratios of peak areas at 280 nm on HPLC analyses; product 35 had a retention time of 16.1 min, and product 36 had a retention time of 24.2 min.

Unidentified impurities.