Acetonide protection of dopamine for the synthesis of highly pure N-docosahexaenoyldopamine

Direct acetonide protection of the catechol of dopamine has proven to be problematic due to the formation of Pictet-Spengler isoquinolines. Here we report an efficient method for acetonide protection of dopamine, allowing the preparation of a dopamine prodrug without complications from the Pictet-Spengler reaction. Acetonide-protected dopamine was first synthesized by pre-protecting the amino group with phthaloyl followed by refluxing with 2,2-dimethoxypropane in the presence of MOH. Further work demonstrated that Fmoc and trifluoroacetyl were also suitable N-protective groups, while Boc-protected dopamine gave an isoquinoline product. Acetonide-protected dopamine was coupled to DHA (all cis-4,7,10,13,16,19-docosahexaenoic acid) to produce the N-DHA-dopamine prodrug with high purity. (C) 2010 Elsevier Ltd. All rights reserved.