SOLUTION CONFORMATIONS OF PATELLAMIDE-B AND PATELLAMIDE-C, CYTOTOXIC CYCLIC HEXAPEPTIDES FROM MARINE TUNICATE, DETERMINED BY NMR-SPECTROSCOPY AND MOLECULAR-DYNAMICS
T. Ishida et al., SOLUTION CONFORMATIONS OF PATELLAMIDE-B AND PATELLAMIDE-C, CYTOTOXIC CYCLIC HEXAPEPTIDES FROM MARINE TUNICATE, DETERMINED BY NMR-SPECTROSCOPY AND MOLECULAR-DYNAMICS, Journal of organic chemistry, 60(13), 1995, pp. 3944-3952
In order to elucidate a possible relationship between the chemical str
ucture and molecular conformation/stability of cytotoxic cyclic hexape
ptides from a marine tunicate, Lissoclinum patella, the solution confo
rmations of patellamides B and C, the chemical structures of which dev
iate from the C-2-symmetry at two positions, were analyzed by means of
H-1-NMR spectroscopy and restrained molecular dynamics simulation. Th
e two molecules took similar twisted ''figure eight-like'' backbone co
nformations without intramolecular hydrogen bonding (type III) in chlo
roform solution. The outline of these cyclic backbone conformations is
similar to that of a related non-C-2-symmetric patellamide D observed
in the crystal structure, but deviates significantly from the ''squar
e form'' (type I) of the C-2-symmetric ascidiacyclamide or the slightl
y structurally deformed patellamide A. Results indicate that preferenc
e for the type I or III conformation is dependent on the degree of asy
mmetry of the side chains attached to the two halves of the C-2-symmet
ric backbone structure. The possible conformation of the cytotoxic cyc
lic hexapeptide is discussed in relation to its biological activity.