Optical resolution and absolute configuration of a nonsteroidal antiinflammatory drug, 2‐(10,11‐Dihydro‐10‐oxodibenzo‐[b,f]thiepin‐2‐yl)propionic acid

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Abstract
The title compound (±)‐1 (CN‐100) was efficiently resolved into a pair of enantiomers by fractional crystallization of the diastereomeric salts of (−)‐and (+)‐1‐phenylethylamine. The purity of the enantiomers was determined using the chiral cellulose column (CHIRALCEL OJ®) which allowed direct separation of the enantiomers. A separation factor (α) of 1.73 was obtained. X‐Ray crystallographic analysis of the (+)‐isomer [salt of (−)‐1‐(4‐bromophenyl)ethylamine] showed that this enantiomer has S‐configuration. Biological studies have shown that only the (+)‐isomer has antiinflammatory activity. Racemization of (−)‐isomer was carried out by heating its propionic acid solution in the presence of mineral acid, such as HBr.