A phenylacetic acid derivative discovered in a high throughp
A phenylacetic nigericin derivative (), discovered in a high throughput screen for CRTH2, inhibited the binding of H-PGD to CRTH2 receptors on 293 cells with an IC of 0.010μM, and inhibited the binding of H-PGD to DP receptors with an IC of only 8.3μM (). Compound also inhibited CRTH2 mediated cell migrations in response to PGD with an IC of 0.0047μM using hCRTH2 stably transfected CEM cells. Compound and many its derivatives (– and –) were synthesized according to . 4-Chloro-3-nitrobenzoyl chloride was reacted with amines to form the corresponding amides. Displacement of the chlorine adjacent to the nitro group with hydroxyphenylacetic acids gave the bis-aryl ethers in good yields. Reduction of the nitro group followed by treatment with sulfonyl chlorides in pyridine afforded the sulfonamides. Compounds , and were synthesized in three steps (), as described in , steps b, c and d. The synthesis of compound is shown in . 4-Chloro-3-nitrobenzaldehyde was protected as the diethyl acetal, which was carried into the same three steps as described in . Finally, the aldehyde was unmasked and converted into the ethyl benzyl amine via reductive amination. Compound () was also synthesized similarly in three steps, as described in . Compounds and were synthesized from compound . Reaction of propionyl chloride with yielded amide and reaction of ethyl isocyanate with afforded urea . The non-commercially available 3-hydroxy-5-chloro phenylacetic acid was synthesized according to . Monochloro displacement of 3,5-dichlorobenzoic acid by methoxide gave 3-chloro-5-methoxybenzoic acid. The carboxylic acid was then converted into the acyl chloride, which was treated with trimethylsilyldiazomethane to afford the diazoketone. Wolff rearrangement of the diazoketone provided the homologated methyl ester. Finally, demethylation afforded 3-hydroxy-5-chloro phenylacetic acid. The optimization began with the examination of the effect of substitutions on the sulfonamide benzene ring (). It was found that the substitutions had little effect on the compounds’ affinity for CRTH2, as the unsubstituted compound has similar potency to other compounds in . However, in vitro metabolic stability studies let us have a preference for the benzenesulfonamides with halogen substitutions, such as the 2,4-dichloro benzenesulfonamide (), because the stability studies using liver microsomes indicated that the benzene ring of the benzenesulfonamides might be a vulnerable site of oxidative metabolism and benzenesulfonamides with alkyl groups or other electron-donating substitutions tend to have less optimal microsomal stability. Next we investigated the role of the ethyl amide moiety. Analogs devoid of the hydrogen bond donor NH, such as tertiary amide and methyl ketone , has significant decreased activity. Likewise, analogs lacking the carbonyl group, such as compounds (compared with ) and (compared with ), also has significantly decreased CRTH2 activity. This data suggests that a hydrogen bond donor and a hydrogen bond acceptor together is likely to be beneficial for the activity on CRTH2, as demonstrated by the primary or secondary amides ( to ), the reversed amide () and the urea () derivatives. Evaluation of the phenylacetic acid moiety revealed that modifications in this part of the molecule affect the selectivity of the antagonists to the CRTH2 and DP receptors (). Compound () and compounds in , that feature the acetic acid moiety to the oxygen-linker are selective for CRTH2 over DP receptor. However, compounds that feature the acetic acid moiety to the oxygen-linker, such as display CRTH2 and DP dual inhibitory activity. Since we were interested in identifying dual antagonists of CRTH2 and DP receptors, we decided to explore the analogs of . Replacement of the acid moiety of with a tetrazole group () maintained the affinity for the DP receptor, but the affinity for CRTH2 was greatly reduced. Likewise, addition of a methyl group at the methylene next to the carboxylic acid () resulted in a moderate enhancement of the affinity for DP, but a significant loss of the CRTH2 affinity.