Preferential enrichment: An essential crystal structure

The crystal structure of (+/-)-[2-[4-(2-hydroxyhexyloxy)phenylcarbamoyl]eth yl]dimethylsulfonium p-chlorobenzenesulfonate [(+/-)-SCC], which failed to effect preferential enrichment due to the chemical modification of the prot otype (+/-)-[2-[ 2-(3-ethoxy-2-hydroxypropoxy)phenylcarbamoyl] ethyl]dimeth ylsulfonium p-chlorobenzenesulfonate [(+/-)-SC] showing preferential enrich ment, has been determined by x-ray crystallographic analysis. The crystalli ne form of (+/-)-SCC is not a mixed crystal of the two enantiomers, but a r acemic compound. In addition, the revised crystal structures of (+/-)-[2-[4 -(3-ethoxy-2-hydroxypropoxy)phenylcarbamoyl] ethyl] dimethylsulfonium p-tol uenesulfonate [(+/-)-ST] and (+/-)-SC, both of which showed preferential en richment, are described. The crystal structure of (+/-)-SCC is different fr om that of (+/-)-SC, but very similar to that of (+/-)-ST. The formation of the crystal phase of the (+/-)-SC type, which can be followed by polymorph ic transition to afford the crystal one of (+/-)-ST type if necessary, stem s to be essential for successful preferential enrichment.