Total Synthesis of Cyclosenegalin A

A Pro-Gly-typed cyclopeptide, cyclosenegalin A, was firstly isolated from Annona senegalensis and Annona scleroderma. In this study, we reported synthesis the cycloheptapeptide with a combination of solid- and solution-phase synthetic methods. This study also compared the effectiveness of β-turn inducer type I and II in cyclosenegalin A to facilitate the cyclization process. The synthesis of cyclosenegalin A were prepared using two different sequences of linear peptides for cyclization. First sequence employed β-turn type I inducer (Ser-Ala-Val-Thr) as turning point and second sequence employed β-turn type II inducer (Thr-Pro-Gly-Leu). The successful cyclization was obtained using the linear sequence of NH₂-Ala-Val-Thr-Pro-Gly-Leu-Ser-OH with β-turn type II. The final product was obtained in 8.2 % yield with PyBOP/DIEA act as coupling agent. The synthetic cyclosenegalin A were characterized with HR-ToFMS, ¹H NMR, ¹³C NMR, HSQC, HMBC, TOCSY, and ROESY. The synthetic product was also evaluated for its antimicrobial activity.