Abstract
AbstractA cyclic heptapeptide, c(Gly‐Ile‐Pro‐Tyr‐Ile‐Ala‐Ala), which was isolated and identified from Stellaria yumumensis French (M), was synthesized by solution method for the first time. Protected heptapeptide Z‐Gly‐Ile‐Pro‐Tyr‐Ile‐Ala‐Ala‐OBzl was synthesized with 3‐(diethoxy‐phosphoryloxy)‐l,2,3‐benzotriazin‐4(3H)‐one (DEPBT) as a coupling reagent. After deprotection of benzyl and benzyloxycarbonyl groups, a free linear heptapeptide H‐Gly‐Ile‐Pro‐Tyr‐Ile‐Ala‐Ala‐OH was cyclized in DMF (2 × 10−3 mol/L) in the presence of nine different metal ions, i. e., Li+, Na+, K+, Cs+, Mg2+, Ca2+, Bai2+, Nr2+ and Cr5+ respectively, using DEPBT as a coupling reagent. Univalent metal ion Cs+ enhanced both the cyclization yield and cyclization rate of H‐Gly‐De‐Pro‐Tyr‐Ile‐Ala‐AlaOH, while some bivalent metal ions, such as Mg2+, Ca2+ and Ni2+ decreased the yields of c (Gly‐Ile‐Pro‐Tyr‐De‐Ala‐Ala) drastically. Trivalent metal ion Cr3+ even inhibited the cyclization reaction completely.
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