4 6 9 × ▁increase ▁at ▁S ERT , ▁with ▁greater ▁aff inity ▁for ▁DAT ▁than ▁c oca ine ▁& ▁was ▁approximately ▁equip ot ent ▁to ▁N ET . ▁ 1 9 7 b ▁was ▁ 1 3 7 × , ▁and ▁ 1 9 6 c ▁ 2 7 × ▁less ▁pot ent ▁at ▁binding ▁to ▁the ▁ser ot on in ▁trans porter , ▁but ▁both ▁had ▁a ▁N ET ▁/ ▁DAT ▁ratio ▁that ▁made ▁for ▁a ▁better ▁dop am iner g ic ▁than ▁c oca ine . ▁ ▁Bio is ost ere ▁ 2 - position ▁car bm eth ox y - ester ▁functional ▁rep lac ements ▁ ▁Ben zo yle c gon ine , ▁i . e . ▁comp ound ▁ 1 9 7 e , ▁( d iffer ing ▁from ▁its ▁c oca ine ▁parent ▁only ▁by ▁de - m eth yl ation ▁of ▁the ▁C 2 ▁car bm eth ox y ▁to ▁that ▁of ▁a ▁car box y ) ▁has ▁an ▁extreme ▁loss ▁in ▁pot ency ▁( its ▁approximate ▁aff inity ▁being ▁ 1 9 5 , 0 0 0 ▁n M ) ▁as ▁displayed ▁by ▁in ▁vit ro ▁method ologies ▁for ▁determ ining ▁binding ▁effic acy ▁( where in ▁B BB ▁pen etr ation ▁does ▁not ▁factor - in ▁on ▁the ▁matter ▁in ▁the ▁manner ▁as ▁in ▁v ivo ▁studies ) ▁and ▁is ▁pos ited ▁to ▁be ▁due ▁possibly ▁to ▁zw itter ion ▁formation . ▁ ▁V iny log ous ▁ 2 β - position ▁car bm