Containing Potential Mercapto Groups

Apparently no data are available for mercapto compounds with hetero atoms-1,2 or for 4-(or 5)-mercapto compounds with hetero atoms-1,3. From the data available, the tautomerism of potential 

For the most part, only compounds of the type 150 151 have been 

OxazoIe-2-thiones have been shown to exist in the thione form (152) 

Although early infrared and chemical data (e.g., reference 175) were interpreted to the contrary, later infrared and ultravio- 

Randall, R. G. Fowler, N. Fuson, and J. R. Dangl, Infrared Determination of Organic Structures. Van Nostrand, New York, 1949. 

For the most part, only compounds of the type 150 151 have been investigated up to the present, and all the evidence available indicates that they exist predominantly in the thione form (151). 

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In recent years there has been a growing interest in the use of polymeric herbicides, pesticides and drugs. Several reviews have appeared on this general area (69-71) and we earlier noted several examples of such potential behavior with poly(vinyl alcohol) modifications. These included modifications containing 6-methylthiopurine (an antileukemia drug) (55), 2,6-dichloro-benzaldehyde (a herbicide) (56), various enzymes (52,53), aspirin (analgesic)(51) and mercapto groups (46-49). 

Six-membered rings are formed by reaction of a three-carbon fragment with an aza heterocycle containing any of (i) an a-methyl, (ii) an a-amino or (iii) a potential a-mercapto group. Examples of... 

Ultraviolet spectra of numerous pyrazines have been recorded, but in many cases without regard to the effects of ionization, and in various solvents. All pyrazines are basic and thus have both neutral (e.g., 5) and cationic (e.g., 6) forms. Pyrazines with a substituent containing an ionizable hydrogen, such as a carboxy, hydroxy, or mercapto group, may also exist in the anionic form (e.g., 7), the tautomeric neutral form (e.g., 2, R = H), a potentially zwitterionic form (8, R = H) or an isomeric cationic form (e.g., 9, R = H). Many published spectra are in fact of mixed ionic species to determine the spectrum of each ionic form it is necessary to measure its spectrum in a solution buffered at least two units above or below the pAa value (or values) of the substance. In nonaqueous solvents, the neutral (uncharged) species are favored. The ultraviolet spectra of pure species may then serve to characterize the pyrazine, may permit the correlation of spectra with structure, and may be used in quantitative determinations. 

Gebelein and coworkers have prepared monomers and polymers based on the antineoplastic agents 5-fluorouracil and 6-mercapto-purine (26). These polymers would be potentially useful in treating various types of cancer or leukemia and some derivatives have shown biological activity. Previous work by this group has Included the synthesis of polyisoprene derivatives containing sulfa drug, carbamate, urea, oxazolldone and oxazole units (27.28). 

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