Grassypeptolides A-C, cytotoxic bis-thiazoline containing marine cyclodepsipeptides.
Grassypeptolides A-C (1-3), a group of closely related bis-thiazoline containing cyclic depsipeptides, have been isolated from extracts of the marine cyanobacterium Lyngbya confervoides. Although structural differences between the analogues are minimal, comparison of the in vitro cytotoxicity of the series revealed a structure-activity relationship. When the ethyl substituent of 1 is changed to a methyl substituent in 2, activity is only slightly reduced (3-4-fold), whereas inversion of the Phe unit flanking the bis-thiazoline moiety results in 16-23-fold greater potency. We show that both 1 and 3 cause G1 phase cell cycle arrest at lower concentrations, followed at higher concentrations by G2/M phase arrest, and that these compounds bind Cu(2+) and Zn(2+). The three-dimensional structure of 2 was determined by MS, NMR, and X-ray crystallography, and the structure of 3 was established by MS, NMR, and chemical degradation. The structure of 3 was explored by in silico molecular modeling, revealing subtle differences in overall conformation between 1 and 3. Attempts to interconvert 1 and 3 with base were unsuccessful, but enzymatic conversion may be possible and could be a novel form of activation for chemical defense.
Department of Medicinal Chemistry, University of Florida, 1600 SW Archer Road, Gainesville, Florida 32610, USA.
Jason C
JC
Kwan
Ranjala
R
Ratnayake
Khalil A
KA
Abboud
Valerie J
VJ
Paul
Hendrik
H
Luesch
D002453:Cell Cycle; D018360:Crystallography, X-Ray; D000458:Cyanobacteria / Q000737:chemistry*; D047630:Depsipeptides / Q000737:chemistry* / Q000302:isolation & purification / Q000494:pharmacology*; D016193:G1 Phase; D020128:Inhibitory Concentration 50; D009682:Magnetic Resonance Spectroscopy; D008387:Marine Toxins / Q000737:chemistry*; D008968:Molecular Conformation; D015394:Molecular Structure; D013329:Structure-Activity Relationship
D047630:Depsipeptides; D008387:Marine Toxins; C555839:grassypeptolide A; C555840:grassypeptolide B; C555841:grassypeptolide C