1.3.4- Oxadiazoles physical properties

Polycyclic oxadiazoles linked to phenyl groups have been prepared. Table 8 compares their physical properties with those of the corresponding polyphenyls the solubility of polyoxadiazoles in organic solvents is much higher and their melting point is lower 18 a). 

The physical properties of 1,2,4-oxadiazoles are unexceptional. The boiling point of the parent compound is 87 °C, within the the normal range of other two-carbon compounds. The heats of vaporization of the first three homologs (39.5-42 kJ moF1) are comparable to that of ethanol. Thermodynamic functions have been calculated over the range... 

The following pages will be devoted mainly to the syntheses, the reactivity, the physical properties, and the uses of 1,3,4-oxadiazoles. 

The tryptophan and quinone classes of IDO inhibitors have been limited by their potency and poor physical properties and to date have not progressed into preclini-cal setting. However, the oxadiazoles identified by Incyte (above, 13-14) represent a new class of competitive IDO inhibitor, which have progressed further toward preclinical development for the treatment of a variety of cancers. 

The physical and chemical properties of the 1,2,4-oxadiazoles are also reviewed in this report. In particular, the stability of the ring system is discussed when only one or no substituent is present, and when the substituents contain functional groups. Attention is also particularly drawn to some novel routes of synthesis leading to the oxadiazole ring. 

The properties (chemical, physical, and spectral) of general ortho (structure I, benzo [d][l,2,3]oxadiazole) and para (structure II, 2-oxa-3,4-diazabicyclo[3.2.2] nona-l(7),3,5,8-tetraene) isomers of diazophenols are very similar indicating that the structures should also be similar. Even though the cyclization and formation of two rings does not seem to be unreasonable for the ortho-isomer, it definitely does not look probable for the para-isomer. It is therefore assumed that the structures I and II are rather improbable for diazophenols [5]. This assumption was confirmed when structure I was prepared and shown to be unstable even in a solid argon matrix. The meta-(3-diazo) isomer has not been reported [5, 6]. 

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