Due to the considerable analgesic potency exhibited by some 2-{4-[(substitutedphenyl)piperazin-1-yl]methyl}isothiazolopyridins of the Mannich base, a series of related compounds with a side chain, which represent a marked departure in the substructure of 4-arylpiperazine [i.e. N-(2pyrimidinyl)piperazine, N-methyl-N′-phenylethylenediamine, 1,2,3,4-tetrahydro-β-carboline, N-cyclohexylpiperazine] was synthesized. 1,2 These compounds were evaluated concerning the toxicity and analgesic action in

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... er to extend the structure-activity (SAR) studies and to find a correlation between the biological activity and the molecular structure within the investigated series and their non-4-arylpiperazine analogues. As a part of these investigations, in this paper we report on the results of an X-ray structure determination of the title 4,6-dimethyl-2-{4-[(2-pyrimidyl)-piperazin-1-yl]methyl}isothiazolo[5,4-b]pyridin-3(2H)-one ( Fig. 1) , which proved to be inactive as an analgesic agent under pharmacological screening. This compound was prepared in a Mannich reaction from 4,6dimethylisothiazolo-[5,4-b]pyridin-3(2H)-one, formaldehyde and commercially available N-(2-pyrimidyl)piperazine. 2 The identity of the investigated compound was established by its IR, 1 H NMR, elementary analysis, and was finally confirmed by an X-ray analysis. Colorless plate crystals suitable for X-ray diffraction analysis were grown by slow evaporation from an 1-heptane solution. X-ray data were collected by graphite-monochromatized Cu Kα radiation at 293 K, ω scans. The structure was solved by direct