ß-cyclodextrin complex formation and protonation equilibria of morphine and other opioid compounds of therapeutic interest.

The inclusion complex formation of morphine and its 18 opioid derivatives with ß-cyclodextrin has been studied using nuclear magnetic resonance spectroscopy. Initially, the protonation equilibria and the acid-base properties of dibasic opioid compounds have been fully characterized. Apparent protonation constants and the relative concentration of the microspecies in cyclodextrin excess were also determined. The 1:1 complex stoichiometry was confirmed by the continuous variation method of Job using UV-VIS spectroscopy. The stability constants of the different protonation forms were determined by 1H NMR titrations. The highest stability was observed in highly alkaline solutions where the amino group is in its unprotonated, neutral state. The structures of the complexes were investigated by two-dimensional ROESY experiments. Based on the stability constants and ROESY experiments, morphine derivatives with longer side chain on the nitrogen atom such as nalbuphine and naltrexone show stronger complexation. The protonation state of the phenolate group, positioned outside the CD cavity, has only a slight influence on the complex stability.

Synthesis of 3-O-Carboxyalkyl Morphine Derivatives and Characterization of Their Acid-Base Properties.

The C-3 phenolic hydroxy group containing morphine derivatives (morphine, oxymorphone, naloxone, naltrexone) are excellent candidates for the synthesis of 3-O-functionalized molecules. Achieving free carboxylic group containing derivatives gives the opportunity for further modification and conjugation that could be used for immunization and immunoassays. For this purpose ethyl bromo- and chloroacetate can be used as O-alkylating agents. Hydrolyzing the products affords the appropriate free carboxylic group containing 3-O-carboxyalkyl derivatives. As these molecules contain an acidic and a basic functional group the protonation macro- and microconstants were determined too, using pH-potentiometry and NMR-pH titration, beside fully characterizing their structure using IR, CD, NMR and HR-MS measurements.

Synthesis of Potential Haptens with Morphine Skeleton and Determination of Protonation Constants.

Vaccination could be a promising alternative warfare against drug addiction and abuse. For this purpose, so-called haptens can be used. These molecules alone do not induce the activation of the immune system, this occurs only when they are attached to an immunogenic carrier protein. Hence obtaining a free amino or carboxylic group during the structural transformation is an important part of the synthesis. Namely, these groups can be used to form the requisite peptide bond between the hapten and the carrier protein. Focusing on this basic principle, six nor-morphine compounds were treated with ethyl acrylate and ethyl bromoacetate, while the prepared esters were hydrolyzed to obtain the N-carboxymethyl- and N-carboxyethyl-normorphine derivatives which are considered as potential haptens. The next step was the coupling phase with glycine ethyl ester, but the reactions did not work or the work-up process was not accomplishable. As an alternative route, the normorphine-compounds were N-alkylated with N-(chloroacetyl)glycine ethyl ester. These products were hydrolyzed in alkaline media and after the work-up process all of the derivatives contained the free carboxylic group of the glycine side chain. The acid-base properties of these molecules are characterized in detail. In the N-carboxyalkyl derivatives, the basicity of the amino and phenolate site is within an order of magnitude. In the glycine derivatives the basicity of the amino group is significantly decreased compared to the parent compounds (i.e., morphine, oxymorphone) because of the electron withdrawing amide group. The protonation state of the carboxylate group significantly influences the basicity of the amino group. All of the glycine ester and the glycine carboxylic acid derivatives are currently under biological tests.