One effective approach to fine tuning the lipophilicity prof

One effective approach to fine-tuning the lipophilicity profile of FFA1 agonists is to ‘decorate’ the 3-phenylpropahoic colorimetric assay scaffold with polar heterocyclic moieties. Alternatively, this scaffold could be replaced with heterocyclic isosteres (as in Takeda’s compounds 1,2 and 3 as well as Amgen’s indole-based compound 4 shown in Fig. 2). Recently, we have reported on the design and synthesis of a series of compounds containing the 3-(1,3,4-thiadiazol-2-yl)propionic acid moiety (cLogP=−0.09) in lieu of the 3-phenylpropanoic acid moiety (cLogP=1.84). The best compound in the series (5) displayed moderate agonist potency against GPR40 (EC50=5.93μM) and an excellent in vitro ADMET profile (plasma protein binding, aqueous solubility and microsomal stability). The lower potency of 5 (compared, for example to TAK-875, GPR40 EC50=0.014μM) can be rationalized by the overly polar character of the 1,3,4-thiadiazole-2-carbozamide used in lieu of the (4-benzyloxy)phenyl moiety (vide supra). In this work, we investigated two compound series that stem from the initial series (represented by compound 5): (i) 1,3,4-thiadiazole-2-carbozamides 6 designed to bring back the lipophilicity of the series (introduction of an additional phenyl ring results in a cLogP increase by two units) and thus improve its potency; (ii) 3-phenylpropanoic acids 7 containing the 1,3,4-thiadiazole-2-carbozamide periphery, designed with the same ‘polar appendage’ approach in mind as explored by us earlier (Fig. 3).
Results and discussion Compounds 6a–e were synthesized from known 2-chloroacetamides 8 according to the previously reported protocol.14, 17 Treatment of 8 with elementary sulfur and morpholine (in the presence of Et3N) gave N-aryl-2-moropholino-2-thiooxacetamides 9. The latter furnished hydrazino adducts 10 on reaction with hydrazine hydrate. Isolated by simple filtration and without further purification (see Section 4), these adducts were transformed, in good to excellent yields, into target compounds 6a–e on reaction with succinic anhydride in glacial acetic acid (Scheme 1). 3-Phenylpropanoic acids 7a–l containing the 1,3,4-thiadiazole-2-carboxamide periphery were synthesized in a similar fashion from 2-chloroacetamides 11. The hydrazino adducts 12 were condensed (via CDI-promoted N-acylation and subsequent cyclodehydration on treatment with HCl) with [4-(3-tert-butoxy-3-oxopropyl)phenoxy]acetic acid (13) which, in turn, was obtained by alkylation of commercially available tert-butyl 3-(4-hydroxyphenyl)propionate (14) with ethyl bromoacetate and subsequent ester hydrolysis (Scheme 2). Both sets of potential GPR40 agonists (6a–e and 7a–l) were tested for FFA1 activation using calcium flux assay conducted on Chinese hamster ovary (CHO) cells engineered to stably express human GPR40. All compounds were tested in concentration–response (% GPR40 activation) mode in order to determine EC50 values, which are presented in Table 1. In analyzing the data on biological activity against FFA1, it should be borne in mind that the anilide periphery in the series of the receptor agonists represented by compound 5 was designed so as to impart higher lipophilicity to otherwise overly hydrophilic 3-(1,2,4-thiadiazol-2-yl)propanoic acid scaffold (vide supra) and thus increase affinity to the receptor. From the data obtained for a even a small set (6a–e) of higher-LogP analogs of compound 5, it becomes apparent that using lipophilicity as a driver of potency against FFA1 was a correct choice. Indeed, four out of five analogs had significantly higher potency compared to 5 (with the best compound, 6a, leading into the sub-micromolar range). The lower potency of 6e most is likely due to conformational rigidity requirement in the portion of the molecule opposite to carboxylic acid functionality, which is present in biphenyl analogs 6a–d and is lost after introduction of the –CH2O– linker in 6e.