Expedious and practical synthesis of the bioactive alkaloids rutaecarpine, euxylophoricine A, deoxyvasicinone and their heterocyclic homologues

Efficient assembly of pyrimido-beta-carbolines 1 and 2, including the bioactive alkaloids rutaecarpine, euxylophoricine A, and deoxyvasicinone (3), is reported from suitable aromatic amino acids 7 or corresponding aromatic amino esters 8 and imino-thio-ethers 5 or 6 in a one-step sequence in moderate to good yields. The key step of this methodology is based on an intramolecular aza-displacement of a methylthio group followed by spontaneous cyclodehydration. Furthermore, when aromatic amino esters 8 were used instead of amino acids, a tandem amino-methylthio displacement/amino ester cyclization takes place. (c) 2006 Elsevier Ltd. All rights reserved.