Improved synthesis of beta-CIT and [11C]beta-CIT labeled at nitrogen or oxygen positions.

The important radiotracer precursor 2 beta-carbomethoxy-3 beta-(4-idophenyl)-tropane (beta-CIT, RTI-55) was made in 52% overall yield from cocaine. Key steps were improved conjugate Grignard addition to anhydroecgonine methyl ester with > 3.5:1 2 beta: 2 alpha-isomer selectivity, and a mild new direct aromatic iodination with I2 and silver triflate in CH2Cl2. The [11C]beta-CIT was labeled at either the N or O positions with [11C]methyl triflate; and efficient reversed-phase HPLC was used to preparatively separate [N-11C]beta-CIT from N-nor-beta-CIT for the first time, and a fast solid-phase extraction (SPE) method was applied to preparatively separate [O-11C]beta-CIT from beta-CIT-acid precursor.