合成路线1

An efficient synthesis of 7(S)-(tert-butoxycarbonylamino)-5-azaspiro[2.4]heptane (XI), a key intermediate in the synthesis of DU-6859a, via an asymmetric microbial reduction has been described: The reaction of N-benzylglycine (I) with tert-butoxycarbonyl anhydride gives N-benzyl-N-(tert-butoxycarbonyl)glycine (II), which is condensed with the potassium salt of ethyl hydrogen malonate (III) by means of carbonyldiimidazole (CDI) in THF yielding 4-[N-benzyl-N-(tert-butoxycarbonyl)amino]-3-oxobutyric acid ethyl ester (IV). The cyclopropanation of (IV) with 1,2-dibromoethane (V) by means of K2CO3 in refluxing acetone affords the cyclopropane derivative (VI), which is cyclized by means of trifluoroacetic acid in dichloromethane to give 5-benzyl-5-azaspiro[2.4]heptane-4,7-dione (VII). The enantioselective microbial reduction of (VII) by means of Phaeocreopsis sp. JCM 1880 in a complex medium containing glucose and polypeptone yields 5-benzyl-7(R)-hydroxy-5-azaspiro[2.4]heptan-4-one (VIII), which by reaction with triphenylphosphine, diethyl azodicarboxylate and diphenylphosphoryl azide (DPPA) followed by reduction with LiAlH4, is converted into 7(S)-amino-5-benzyl-5-azaspiro[2.4]heptane (IX). The protection of (IX) with tert-butoxycarbonyl anhydride as usual gives the protected amine (X), which is finally debenzylated by hydrogenation with H2 over Pd/C in ethanol affording the desired 7(S)-(tert-butoxycarbonylamino)-5-azaspiro[2.4]heptane (XI).