Mechanistic study on exchange between labeled cyanide and nitriles

The potential of a clean, rapid exchange between the nitrile function of mandelonitrile and cyanide was examined for the preparation of labeled mandelonitrile which could be subsequently rapidly reduced with borane to labeled phenylethanolamine (PEOH). The mandelonitrile exchange (CN-CN) was studied using [13C]-NaCN with crown ethers in THF, monitoring the results with 13C-NMR. A large increase in the intensity of the signal due to [13C]-nitrile was observed. The exchange was also carried out using [14C]-NaCN, and the exchanged nitrile was reduced to [14C]-PEOH. The chemical yield for the reduction of [14C]-mandelonitrile to [14C]-PEOH was 60% and the overall radio-chemical yield of the cyanide-exchange and borane reduction (based on [14C]-NaCN used) was 20%. Mechanisms are proposed which were found to be consistent with results of cyanide exchange of appropriately selected nitriles. (author)