The purpose of the present study was to synthesize and characterize novel thiolated polymers mediated by carbodiimide. Cysteine was covalently linked to sodium carboxymethyl starch (CMS) and carboxymethyl guar gum (CMG). Depending on the weight-ratio polymer to cysteine during the coupling reaction, the resulting CMGCysteine conjugates displayed 80% ± 2.6 thiol groups per gm of polymer were as CMS-Cysteine conjugates displayed 78% ± 2.1. (mean ± S.D.; n=3).In aqueous solution above pH 6.0 polymers were capable of forming interand/ or intra-molecular disulfide bonds. Mucoadhesion studies carried out on freshly excised sheep intestinal mucosa. The CMS-Cysteine displayed less mucoadhesion where as CMG-Cysteine conjugate were displayed increased mucoadhesion. The swelling behaviour of the CMS-Cysteine conjugate was influenced by the covalent attachment of the sulfhydryl compound. In contrast the swelling behaviour of CMG-Cysteine was not influenced by the immobilisation of cysteine. Furthermore, in aqueous solutions the cumulative % drug release time of tablet based on the CMG-Cysteine was prolonged 1.5 fold as compared to tablet containing CMS-Cysteine conjugate. Due to a high crosslinking tendency by the formation of disulfide bonds stabilizing drug carrier systems based on thiolated polymers and permeation enhancing effect, CMG-Cysteine conjugates represent promising excipients for the development of novel drug delivery system.
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