or in which the benzothiazole nucleus is reduced, are described. The compounds were prepared as non-photosensitizing antimicrobial agents and the relationships between structure and these properties are discussed. 2-Benzylthiobenzothiazole basic ethers show greater activity against bacteria, fungi, and protozoa than the compounds described previously.IN Part I11 the preparation of some 2-phenylbenzothiazole basic ethers was described and from these 5-chloro-2-(~-2-diethylaminoethoxyphenyl) benzothiazole was chosen for clinical investigation. This substance proved to be an effective topical fungicide but was found to possess biological photosensitizing properties (see Discussion). A study was therefore made of the relationships between structure , photosensitizing properties, and anti-microbial activity with the object of devising new non-irritant antifungal agents. This report deals with the chemistry and ultraviolet absorption spectra of 2-substituted benzothiazole basic ethers differing from those described in Part I11 in that the phenyl and benzothiazole nuclei are not directly linked, or in which the benzothiazole nucleus is reduced.The photosensitizing 2-phenyl-compounds previously described have absorption peaks in the 315-330 mp region and, although in general such photosensitization results from the absorption of a wide spectrum of radiation, the effects produced by these compounds may be related, as in the case of the furocoumarins,2 to a specific range of wavelengths. In the case of the related 2-methylbenzothiazoles there is no photosensitization and absorption only occurs below 300 mp. Since the lower limit of solar ultraviolet radiation is in the region of 290 mp it is probable that compounds whose principal absorption maxima are below this limit will not cause photosensitization. The problem of overcoming photosensitivity could therefore be approached by reducing the conjugation in the 2-phenylbenzothiazole system so that light absorption occurred at lower wavelengths and for this reason compounds of type (111), in which the conjugation between phenyl and benzothiazole rings is broken, were prepared.In a first group of compounds a single atom separated the two rings (111; Y = CH,, S, NH, or 0) and these compounds had absorption peaks at wavelengths lower than that shown by 5-chloro-2-(~-2-diethylaminoethoxyphenyl) benzothiazole. The compounds were not photosensitizers but possessed no significant anti-microbial activity. In a second group, a two-atom chain was introduced between the rings (111; Y = CH,*CW,, SCH,, CH,-S, NHCH,, CH,*NH, or CH,*O) and two benzylthiobenzoxazoles were also prepared. The compounds again had maximum absorption at lower wavelengths and were not photosensitizers but, in the case of phenethyl-and benzylthio-compounds, antifungal activity comparable with that shown by the compounds described in Part I11 was obtained. The relationship between structure and anti-microbial activity in these two series was therefore more closely investigated by the preparation of compounds in whic...
