Structural studies of FR900359, a novel cyclic depsipeptide from Ardisia crenata sims(Myrsinaceae)
The molecular structure and absolute configuration of FR900359, a novel cyclic depsipeptide from Ardisia crenata sims, has been determined by a combination of X-ray crystallographic analysis and g.c./m.s. study of the diastereomeric derivatives of its constituents. There are five intramolecular hydrogen bonds (or short contacts) in the FR900359 molecule. All the imino nitrogen and hydroxy oxygen atoms having a proton-donating ability efficiently participate in the hydrogen bond network. The FR900359 molecule contains two cis peptide bonds, in a conformation which can take part in the hydrogen bonds. This hydrogen bond network contributes to the stabilization of the overall structure of FR900359; constituents not restrained by this network are considered to be flexible. Since the N-methyldehydro-L-alanine residue falls within the unstable region of a Ramachandran (φ–ψ) plot, it is vulnerable to nucleophilic attack and may, therefore, be involved in the biological activity of FR900359.