Azapentalenes, aromatic biological activity

In the first part of this review we deal with the concept of heteroaromaticity and consider the aromaticity of heteropentalenes, particularly azapentalenes. Methods of synthesis, chemical reactivity, and spectroscopic properties are dealt with, and the review ends with a brief survey of their industrial uses and biological activity. 

Table VII lists biological activities that have been found for some aromatic azapentalenes. Among these, imidazo[2,l-6]thiazoles have probably been most studied, and this has partly followed the discovery454 that a tetrahydro derivative 480 possessed marked anthelmintic activity. This compound is marketed as Tetramisole (or as the L-isomer, Levamisole) and is at present one of the most effective agents for the treatment of roundworm infestations. Anthelmintic activity has been found for aromatic imidazo[2,l-6]thiazoles (Table VII), and it has been suggested331 that a 6-aryl substituent is necessary for activity in this series.

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