Synthesis and Chemical Structure of the Cyclic Heptapeptide Stylissamide H

We investigated the chemical structures and conformational
isomers
of the cyclic heptapeptides stylissamide H and euryjanicin A isolated
from marine sources. Despite sharing the same molecular structure,
stylissamide H and euryjanicin A exhibit different conformational
isomers in solution and solid states. The main difference arises
from the cis/trans configurations of the two Pro
residues. We prepared stylissamide H using Fmoc solid-phase peptide
synthesis and investigated its chemical structure in the solution
state and the solid state via NMR spectroscopy and X-ray crystallography,
respectively. The results indicated that the s-trans,cisPro conformer of stylissamide
H is more stable in solution, whereas the s-cis,cisPro conformer is more stable in the solid state.
We concluded that stylissamide H and euryjanicin A are the same molecules.

本研究针对从海洋生源中分离得到的环状七肽 (cyclic heptapeptide) Stylissamide H与Euryjanicin A的化学结构及构象异构体展开探究。尽管二者拥有完全相同的分子结构，但Stylissamide H与Euryjanicin A在溶液态与固态下呈现出不同的构象异构体。二者的构象差异主要源于两个脯氨酸（Pro）残基的顺反构型。本研究采用Fmoc固相多肽合成 (Fmoc solid-phase peptide synthesis) 法制备了Stylissamide H，并分别通过核磁共振波谱法 (NMR spectroscopy) 与X射线晶体学 (X-ray crystallography) 对其溶液态与固态的化学结构进行了表征。研究结果表明，Stylissamide H的s-反式、顺式脯氨酸构象异构体在溶液中更为稳定，而其s-顺式、顺式脯氨酸构象异构体在固态下更稳定。本研究最终得出结论：Stylissamide H与Euryjanicin A为同一分子。