Synthesis and in vitro biological evaluation of a carbon glycoside analogue of morphine-6-glucuronide

Attachment of a glucose moiety to 6-β-aminomorphine afforded compound 3, where the glucose moiety was linked to the C-6 nitrogen atom by a two-carbon bridge. The synthesis of 3 was accomplished in eight steps from 3-triisopropylsilyl-6-β-aminomorphine and 2,3,4,6-tetra-O-benzyl-d-glucose. The C-glycoside 3 was prepared with the objective of examining a metabolically stable analogue of morphine-6-glucuronide and determining the potency and selectivity of opioid receptor binding. Competition binding assays showed that 3 bound to the μ opioid receptor with a Ki value of 3.5 nM. The C-glycoside 3 exhibited δ/μ and κ/μ selectivity ratios of 76 and 165, respectively. The synthetic intermediate (i.e., benzyl precursor, compound 11) bound to the μ opioid receptor with a Ki value of 0.5 nM, was less selective for the μ opioid receptor. The [35S]GTPγS assay was used to evaluate the functional properties of compounds 3 and 11. Compound 3 was determined to be a full agonist at the μ opioid receptor, whereas compound 11 was found to be a partial agonist. Compound 3 was determined to be very stable in the presence of human liver S9, and rat and monkey liver microsomes: no detectable loss of 3 was observed up to 90 min. Compound 3 was also very stable at pH 2 and pH 7.4, suggesting that 3 possessed properties for sustained duration of action.