A CD method for determination of the absolute stereochemistry of acyclic glycols. 1. Application of the CD exciton chirality method to acyclic 1,3-dibenzoate systems

Absolute Stereostructures of Cell-adhesion Inhibitors, Peribysins A, E, F and G, Produced by a Sea Hare-derived Periconia sp.

“…Based on the above evidence, peribysin G (3) was found to be the C-7 stereoisomer of peribysin F (2). The absolute configuration of 3 was elucidated by application of CD spectrum [10]. Bis-pbromobenzoate 8 derived from peribysin G (3) exhibited positive first and negative second Cotton effect [253 nm (De ϩ8.8) and 238 nm (D e Ϫ4.5)] in the CD spectrum.…”

Configuration of heptopyranoside and heptofuranoside side chains: 2-anthroate, a powerful chromophore for exciton coupled CD

“…Proof that conformer A is the major contributor to the overall conformation of 19a comes from the vicinal coupling constants of J 1,2 = 6.8 (trans) and 3.6 Hz (gauche), indicating that the dihedral angles between the two protons are different. 7 Harada et al have also shown by MO theoretical calculations (MOPAC Ver. 7.0, AM1 program) that conformer A is the most stable.…”

“…A simple approach for the determination of the absolute configuration of such systems employing the exciton chirality method is described by Harada et al 7 Based on this method, the 1,2-diols are derivatized with p-substituted benzoate chromophores and the CD of the derivatives are measured. Derivatization, for example, of (2S)-1,2-propanediol 18 ( Fig.…”

“…3) with p-bromobenzoate furnishes compound 19a, which gives a positive CD bisignate curve in EtOH, 236 nm (−6)/253 nm (+15), A = +21. 7 Compound 19a can exist in three distinct conformations, A, B, and C, of which A and B lead to opposite CD exciton couplets. The exciton coupling of conformer C should be almost zero and therefore this conformation can only influence the amplitude but not the sign of the bisignate curve.…”

“…Many methods (reference 5 and references therein) have been developed over the years, including a difference CD approach reported by Mori et al 6 and a monochromophoric derivatization approach and exciton coupling between identical benzoate chromophores reported by Harada et al 7 and Uzawa et al 8 In the latter method, the absolute configurations of various diols have been assigned in an unambiguous manner. However, the CD spectra are sensitive to changes in the steric effects of substituents, and hence additional data regarding confor-mational distribution is usually required.…”