Skip to main content
. Author manuscript; available in PMC: 2018 Jul 5.
Published in final edited form as: Tetrahedron Lett. 2017 May 25;58(27):2675–2680. doi: 10.1016/j.tetlet.2017.05.084

Table 1.

Optimization and evaluation on cyclization efficiency of linear hexapeptide precursors with different amino acid sequence.

graphic file with name nihms882555u1.jpg
Entry Linear hexapeptide substrates HO-AA1AA2AA3AA4AA5AA6-NH2 Linear yield (%) tR (min)a Linear purity (%)b Cyclic yield (%)c
1 HO-Asn(trt)-Val-d-Leu-Leu-Trp(boc)-d-Orn(boc)-NH2 (10) 55 6.93 100 (100) 72
2 HO-Val-d-Leu-Leu-Trp(boc)-d-Orn(boc)-Asn(trt)-NH2 (12) 49 6.92 98.2 (98.6) 65d
3 HO-d-Leu-Leu-Trp(boc)-d-Orn(boc)-Asn(trt)-Val-NH2 (13) 57 6.87 98.9 (98.6) 63
4 HO-Leu-Trp(boc)-d-Orn(boc)-Asn(trt)-Val-d-Leu-NH2 (14) 58 6.89/6.90 98.7 (99.7) 77
5 HO-Trp(boc)-d-Orn(boc)-Asn(trt)-Val-d-Leu-Leu-NH2 (15) 53 6.90 99.6 (98.0) 65
6 HO-d-Orn(boc)-Asn(trt)-Val-d-Leu-Leu-Trp(boc)-NH2 (16) 52 6.85 99.5 (99.6) 68
a

HPLC retention time.

b

Determined by HPLC analysis at 254 and 220 nm, respectively.

c

Yield refers to isolated peptides after silica gel column chromatography.

d

Desired product 11 (41%) and C-terminal d-Val epimer 18 (24%).