A series of quaternary 2-phenylimidazo[1,2-a]pyridinum salts has been prepared and evaluated for antiparasitic activity. Primary attention was focused on derivatives with amido, substituted hydrazone, and heterocyclic functionality at the para position of the phenyl substituent. Guanylhydrazones and N-substituted guanylhydrazones of the 4'-formyl-substituted compounds are very active against the blood state Trypanosoma rhodesiense in mice by subcutaneous or oral administration. The most potent compounds attain 100% survival for 30 days at doses of less than 1.0 mg/kg (sc) and greater than 5.0 mg/kg (po). Weaker activity is noted for certain other 4'-substituents such as carboxamidines and carboxamide oximes. Considerable variation in structure, including replacing of the imidazo [1,2-a]pyridinium ring by other cationic heterocyclic rings and insertion of linking groups between the heterocyclic ring and phenyl group, can be done, and a high level of activity is maintained. Relationships between these structural changes and biological activity are discussed.

A series of substituted 2‐aryl imidazo[1,2‐a]pyridines has been prepared in which a variety of substituents are introduced on the 4′‐position of the phenyl ring and on the 3, 5, 6 or 7 position of the heterocyclic ring. Most examples have acetamido, bromo, cyano, or formyl substituents at the 4′‐position. Analogous imidazo‐[2,1‐b]fhiazoles and imidazo[1,2‐a]pyrimidines have also been prepared. Another series of compounds consisting of 4′‐formylphenoxymethyl derivatives of imidazole, the three positional isomers of pyridine, thiazole, benzimidazole and ring‐substituted imidazo[1,2‐a]pyridines has been prepared. 2‐(4′‐Formylphenylethenyl) derivatives of imidazole and imidazo[1,2‐a]pyridine were also prepared.

Disulfur monoxide (S20) reacts with 2,3-disubstituted butadienes to form 4,5-disubstituted 3,6-dihydro-l,2dithiin 1-oxides. The structure of 4,5-diphenyi-3,6-dihydro-1,2-dithiin 1-oxide (3) was established by independent synthesis. Reaction of cisor

ROTATIONAL SPECTRUM OF WATER 1165 borhood of the 131 cm-I quartz absorption. The overall agreement is ±0.014 cm-I (rms deviation). For the energy levels presented in Ref. 2 it was possible to make 39 comparisons. Again excluded were blended lines, the lines seen in the 131-cm-1 region, and additionally one other line.o The over-all agreement is ±0.011 cm-I 5 It appears that the value of the 927 energy level as given in Ref. 2 is in error. It should be 0.100 cm-1 lower. K. N. Rao (private communication) has confirmed this. THE JOURNAL OF CHEMICAL PHYSICS (rms deviation) with the line involving the 927 energy level being excluded. The agreements are comparable, with a slight preference for the energy levels derived from the near-infrared data. ACKNOWLEDGMENT

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