Chiroptical and Conformational Studies of Optically Active 2-Aryl-2H-1, 4-benzothiazin-3(4H)-one Derivatives, Related Compounds with a Novel Ca²⁺ Antagonist, Semotiadil (SD-3211)

Abstract

Chiroptical properties of (R)-(+)- and (S)-(-)-2-(2-hydroxy-5-methoxyphenyl)-4-methyl-2H-1, 4-benzothiazin-3(4H)-one ((R)- and (S)-2), and (S)-(-)-4-methyl-2-phenyl-2H-1, 4-benzothiazin-3(4H)-one ((S)-3), related compounds with a novel Ca²⁺ antagonist, Semotiadil ((R)-1; SD-3211), were reported. The absorption band of each chromophore was assigned by reference to the ultraviolet (UV) spectra of 2-unsubstituted benzothiazine (4) and thiazine (5); in the circular dichroism (CD) spectra of (R)-2, (S)-2 and (S)-3, their maximum wave lengths corresponded approximately to those of the UV absorptions of each chromophore. The CD spectra suggested that the conformation of (S)-3 was similar to that of (R)-2 and (S)-2, in contrast to the X-ray crystallographic result previously analyzed. The solution conformations of these compounds were discussed by reference to the helicity rule.