Effect of nitrogen insertion on the antitussive properties of menthol and camphor

Aromatic vapors of monoterpenoids such as menthol and camphor are known to possess antitussive effects for the symptomatic relief of upper respiratory tract. The lactams 10 and 11 of menthol and camphor, respectively, have been synthesised and evaluated first time for their antitussive activity in citric acid-induced cough in guinea pig model. The effect of nitrogen insertion in the chemical architecture of menthol and camphor on the antitussive activity was reflected by the significant decrease of the cough frequency and increase in the cough latency exhibited by aerosolized 10 and 11. Prior exposure of aerolsolised 10 for 5 min at different concentrations (15, 30, and 60 μg/l) significantly reduced cough response induced by citric acid and also increased latency to initial cough response. Similarly 11 has showed greater inhibitory cough response in comparison to camphor at concentrations such as 125, 250, and 500 lg/l. However, latency to initial cough response was only increased at the concentrations of 250 and 500 μg/l.