GABA-analogous spirocyclic amino acid esters, 5. n-benzyl-7-azaspiro[4.5]decane-l-carboxylates

N-Benzyl-7-azaspiro[4.5]decane-1-carboxylates (4a and 4b) were prepared in a seven step synthesis starting from ethyl cyclopentanonecarboxylate (5). Aminolysis of the ß-keto ester (5) with benzylamine led to the ß-keto amide (9) which gave the a-substituted ß-keto amide (10) by addition of acrolein. Reduction of 10 with LiAlH4 resulted in a reductive cyclization yielding a mixture of the epimeric spirocyclic alcohols (12a and 12b, 3:1). Oxidation of the alcohols (12a and 12b) was archieved with (COCl)2/DMSO giving the spirocyclic ketone (14). Treatment of 14 with tosylmethyl isocyanide and tert-BuOK yielded a mixture of diastereomeric nitriles (15a and 15b, 6:4) which was separated by chromatography. Hydrolysis and esterification of 15a and 15b led to the diastereomerically pure amino acid esters (4a and 4b) which represent novel analogs of GABA with restricted conformational flexibility.