Azo-containing urethane analogues for colonic drug delivery: synthesis, characterization and in-vitro evaluation

A urethane‐based analogue containing an azo aromatic linkage in the backbone was synthesized for use in colon‐specific delivery systems by reacting toluene‐2,6‐diisocyanate with a mixture of an aromatic azo diol, (bis‐4‐hydroxyphenyl)‐4,4′‐diazobiphenyl, poly(ethylene glycol) (Mn = 4000; number‐average molecular weight) and 1,2‐propanediol (propylene glycol). The resultant compounds (UR‐1 and UR‐2) were characterized by IR spectroscopy, 1H NMR spectroscopy, DSC studies, X‐ray diffraction studies and molecular weight determination by gel permeation chromatography. The compounds exhibited low molecular weight, lacked film‐forming properties and crystallinity in the structure. An in‐vitro bacterial degradation test to demonstrate the susceptibility of azo bond to bacterial enzymes was performed using media inoculated with lactobacillus culture. The results indicated degradation of films by azoreductase. In‐vitro permeation of 5‐aminosalicylic acid was studied in control and lactobacilli‐treated films. The permeability of the lactobacilli treated films was significantly increased suggesting the potential of these compounds for application in colonic targeting.