QSAR for upper-respiratory tract irritation.

A recent paper by Muller and Greff (Fd. Chem. Toxicol., 22 (1984) 661) presents QSAR equations for upper respiratory tract irritation by compounds falling into various chemical families. In the present paper the relationships are analysed further. It is found that a general QSAR equation, covering a diverse range of structures, correlates the biological activity reported by Muller and Greff with a single physicochemical parameter, TB'. The parameter TB' is the boiling point at atmospheric pressure (TB), adjusted for compounds with Trouton constants different from 22 cal deg-1 mol-1: TB' = (Tr X TB/22) + 40(1 - Tr/22) where Tr is the Trouton constant. Some of the compounds studied were found to be more irritant than predicted by the general equation: their enhanced activity can be rationalised in terms of their chemical reactivity as electrophiles, their metabolism to electrophiles, or their hydrolysis to more irritant products.