Table 2.

Relative Exchange Efflux Rate, Uptake Inhibition of [³H]-Gabapentin, and IC₅₀ Values in HEK-hLAT1 Cells for α-Substituted Phenylalanine Derivatives

Compounda	R’	%L-Phe Effluxb	% Inhibitionc	IC50 (μM)d
50 (L-Phe)	H	100	85	69 ± 29
50-D (D-Phe)	H	96	74	46 ±23
92	Me-	$\overline{100}$	-	130 ±28
92-D	Me-	$\overline{100}$	-	810 ±350
93	PhCH2 (achiral)	23	11	-
94	(CH3)2CHCH2-	19	15	-
94-D	(CH3)2CHCH2-	27	2.1	-
98	CH3S(CH2)2-	56	21	240 ± 63
98-D	CH3S(CH2)2-	27	−0.20	-
107		13	19	-

^aCell assay data was obtained at least in triplicate (wells). Amino acids were either purchased (50, 93), synthesized according to Scheme 2 (92), or as previously published (98,⁸² 107^83,84). All compounds above are either single enantiomers of l configuration, or achiral (93), with the exception of the following compounds: 94-D (86% ee), 98 (78% ee), 98-D (80% ee), as determined by chiral HPLC analysis (Supporting Information).

^bCompounds were tested at 200 μM for their ability to cause efflux (fmol/min) of [³H]-gabapentin from preloaded HEK-hLAT1 cells. Efflux of [³H]-gabapentin was calculated at 3 min after adding test compound. %Efflux was normalized relative to L-Phe (50), which had an efflux rate of 2.7 ± 0.3 fmol/min, from an average of seven experiments.

^cCompounds were tested at 200 μM for their ability to inhibit uptake of [³H]-gabapentin into HEK-hLAT1 cells. Data are presented as % inhibition relative to background signal in the absence of a test compound.

^dFor IC₅₀ determinations, varying concentrations of each compound were added, from 0.1 to 500 μM. IC₅₀ and standard deviation of each compound were calculated by Graphpad Prism version 5.0. %[³H]-gabapentin uptake at each concentration was normalized relative to %inhibition by BCH^80,81 at 2 mM, which was set to 100% inhibition.