Three challenges toward the assignment of absolute configuration of gymnocin-B.
The absolute configuration of gymnocin-B has been determined to be (S)-10 and (S)-37. Three challenges toward the configurational assignment of this largest of the polyether marine toxin include (i) introduction of p-(meso-triphenylporphyrin)-cinnamate group (TPPcinnamate) on sterically hindered 10-, 37-hydroxyls under mild conditions, (ii) conformational analysis in the presence of TPPcinnamates at C-10 and C-37 positions on the flexible seven-membered rings embodied in a large polyether ladder-like scaffold structure, and (iii) determination of the chirality at C-10 and C-37 on the basis of porphyrin/porphyrin circular dichroism exciton-coupled interaction over a large distance. The experimentally obtained positive exciton couplet by CD and FDCD of the bis-TPPcin derivative of gymnocin-B is in good agreement with that of theoretically calculated CD of the MMFF optimized structures, by employing DeVoe's coupled oscillator approach, thus establishing the full absolute configuration of gymnocin-B.
Tanaka
Katsunori
K
Department of Chemistry, Columbia University, 3000 Broadway, New York, New York 10027, USA.
Itagaki
Yasuhiro
Y
Satake
Masayuki
M
Naoki
Hideo
H
Yasumoto
Takeshi
T
Nakanishi
Koji
K
Berova
Nina
N
D002934:Cinnamates / Q000737:chemistry*; D002942:Circular Dichroism; D004988:Ethers, Cyclic / Q000737:chemistry*; D008968:Molecular Conformation; D015394:Molecular Structure; D011166:Porphyrins / Q000737:chemistry*; D013237:Stereoisomerism
D002934:Cinnamates; D004988:Ethers, Cyclic; D011166:Porphyrins; C505754:gymnocin-B