Tunicyclin L, a cyclic peptide from Psammosilene tunicoides: Isolation, characterization, conformational studies and...

Tunicyclin L (1), cyclo (L-Pro¹-Gly-L-Phe¹-L-Ile-L-Pro²-L-Phe² -L-Thr-L-Val), and 11 known compounds, including one cyclic peptide (2), eight carboline alkaloids (3 -10), one lignan (11) and one flavone (12) were isolated from the roots of Psammosilene tunicoides. Their structures were elucidated on the basis of extensive UV, IR, MS, NMR spectroscopic data and comparison with literature. Single-crystal X-ray diffraction results revealed the stereochemistry of the 24-membered ring cyclic peptide (1). Among these known compounds, compound 6 was found to be a new natural product, and compounds 3, 4, and 11 were isolated from this plant for the first time. Five compounds (1, 3, 4, 7, and 9) showed moderate anti-acetylcholinesterase (AChE) activity.