New cytotoxic cyclic peptides and dianthramide from Dianthus superbus

Four new cyclic peptides, dianthins C-F (1-4), and a new dianthramide, 4-methoxydianthramide B (5), were isolated from the MeOH extract of the traditional Chinese medicinal plant Dianthus superbus. The sequences of cyclic peptides 1-4 were elucidated as cyclo(Gly¹-Pro²-Phe ³-Tyr⁴-Val⁵-Ile⁶-), cyclo(Gly ¹-Ser²-Leu³-Pro⁴-Pro ⁵-Ile⁶-Phe¹-), cyclo(Gly¹-Pro ²-Ile³-Ser⁴-Phe⁵-Val⁶-), and cyclo(Gly¹-Pro²-Phe³-Val ⁴-Phe⁵-) on the basis of ESI tandem mass fragmentation analysis, chemical evidence, and extensive 2D NMR methods. The conformation of compound 1 was established as an α-helix by CD analysis. Furthermore, compounds 3 and 5 showed cytotoxicities toward the Hep G2 cancer cell line with IC₅₀ values of 2.37 and 4.08, respectively.