In addition several other considerations were
In addition, several other considerations were made for the optimization exercise. While the structural features of the endogenous ligands for long-chain fatty ezh2 pathway receptors suggest obtaining orthosteric agonists with drug-like properties may be challenging, the optimization efforts were committed to maintaining molecular weight in the range of compound (MW<400) while hoping to realize high plasma drug concentrations, as plasma protein binding was expected to limit the free fraction of the drug. With these goals in mind, our efforts directed toward the identification of improved small molecule FFA4 agonists commenced. The general synthesis of the phenylpropanoic acid agonists is shown in . Alkylation of substituted 4-hydroxyphenylpropanoic esters with substituted benzyl halides or benzyl alcohols followed by ester hydrolysis directly yielded the desired phenylpropanic acids. The ease of synthesis of the desired compounds coupled with the commercial availability of the starting materials allowed for rapid SAR generation. Phenylpropanoic acid headgroups were prepared as shown in . In general, ketone or benzaldehyde derivatives ( were olefinated and reduced to provide the corresponding propanoates (, which in some cases required demethylation (BBr) to provide the desired phenols. Hydroxyl derivative was obtained via the aldol reaction of the corresponding benzaldehyde derivative () with bis-lithiated species of acetic acid. The phenylpropanoic acid derivative for alcohol was obtained from the corresponding aldehyde () which in turn was prepared by a titanium-mediated formylation/deprotection sequence from . Isobutyl derivative was prepared by the Mitsunobu-initiated Claisen-rearrangement of the corresponding phenol (, R′=H) with 2-methyl-2-propenol followed by alkene reduction to afford intermediate . Benzyl alcohols and their activated derivatives were prepared as outlined in . Benzoic acids with the desired 2,5-disubstitution pattern were reduced directly to the desired benzyl alcohol derivatives (). Variation of ether group at the 2-position holding the 5-methyl substituent constant () was accomplished starting from 5-methyl salicylic acid by simple alkylation followed by reduction. Formylation of 4-trifluoromethyl phenol followed by reduction and conversion to the mesylate derivative allowed for incorporation of a trifluoromethyl group at the 5-position of the benzyl alcohol derivatives. 5-Methyl-3-alkoxy-disubstituted benzyl alcohols were prepared starting from 3-methoxy-5-bromobenzene utilizing a sequence consisting of deprotection followed by alkylation to furnish bromide , which underwent subsequent metal-halogen exchange and trapping to provide the intermediate aldehyde which was reduced to afford the desired benzyl alcohol derivatives (). Select compounds were derivatized following construction of the benzyl ether bond (), for instance, compounds containing 5-methyl-3-alkoxy substitution on the benzyl tail were prepared starting from 3,5-dimethylbromobenzene. Radical halogenation followed by benzyl ether formation provided the arylbromide intermediate which underwent palladium catalyzed etherification followed by saponification to provide the desired diphenylether . Our initial studies explored substitution about the phenylpropanoic acid headgroup while holding a 2-thiotrifluoromethylbenzyl tail constant (). Parent compound provided a nearly balanced FFA1/FFA4 (2-fold selective for FFA4) starting point and it was hoped that further improvements in potency for FFA4 could be realized utilizing the benzyl tail of compound . Addition of polarity ( & ) along the propanoic acid chain or simple substitution () eroded activity at both receptors. Incorporation of a methyl substituent at R2 () or dimethyl substitution at R3 and R5 () provided no improvement in potency, while methyl substitution at R3 () increased activity at FFA4 while diminishing FFA1 activity. Dimethyl substitution () provided a selective FFA4 agonist while growing the substitution in the form of a naphthalene ring () led to diminished activity at FFA4. Small nonpolar substituents at R3, such as the chloro group of , provided a further improvement in FFA4 potency and afforded excellent selectivity over FFA1, which stands in contrast to the incorporation of more polar ( & ) or larger () R3 substituents which led to a reduction in activity at both receptors.