Tetrahydro-pyrrolo-[2,3-b]indole-1,2,8-tricarboxylic acid ester in the enantiospecific preparation of α-methyltryptophan: Application in the preparation of carbon-14 labeled PD 145942 and PD 154075

Article abstract of DOI:10.1002/(SICI)1099-1344(199712)39:12<1019::AID-JLCR43>3.0.CO;2-T

[2R-(2α,3aβ,8aβ)]-2,3,3a,8a-Tetrahydro-pyrrolo[2.3-b]indole-1,2,8 -tricarboxylic acid-1,8-dibenzyl ester 2-methyl ester, its [2S-(2β,3aα,8aα)]-isomer, and the tribenzyl ester analogs were prepared. From these [2,3-b]indole-1,2,8-tricarboxylic acid esters we accomplished a simple, high yielding preparation of enantiopure α-methyltryptophan and methyl ester derivatives. Using this protocol, we inexpensively made (R)-α-[¹⁴C]methyltryptophan methyl ester, and in subsequent reactions converted it into [1-(2-hydroxy-cyclohexylcarbamoyl)-2-(1H-indol-3-yl)-1 -[¹⁴C]methylethyl]carbamic acid adamantan-2-yl ester (PD 145942) and [2-(1H-indole-3-yl)-1-[¹⁴C]methyl-1(1-phenyl-ethylcarbamoyl)-ethyl]carbamic acid benzofuran-2-yl methyl ester (PD 154075). Both of these compounds are drug candidates in preclinical study for the treatment of anxiety and emesis respectively.