5-alkyl-1,3-oxazole derivatives of 6-amino-nicotinic acids as alkyl ester bioisosteres are antagonists of the P2Y12 receptor.

BACKGROUND: Recently, we reported ethyl nicotinates as antagonists of the P2Y12 receptor, which is an important target in antiplatelet therapies. A potential liability of these compounds was their generally high in vivo clearance due to ethyl ester hydrolysis. RESULTS: Shape and electrostatic similarity matching was used to select five-membered heterocycles to replace the ethyl ester functionality. The 5-methyl and 5-ethyl-oxazole bioisosteres retained the sub-micromolar potency levels of the parent ethyl esters. Many oxazoles showed a higher CYP450 dependent microsomal metabolism than the corresponding ethyl esters. Structure activity relationship investigations supported by ab initio calculations suggested that a correctly positioned alkyl substituent and a strong hydrogen bond acceptor were necessary structural motifs for binding. In rat pharmacokinetics, the low clearance was retained upon replacement of an ethyl ester with a 5-ethyl-oxazole. CONCLUSION: The use of shape and electrostatic similarity led to the successful replacement of a metabolically labile ethyl ester functionality with 5-alkyl-oxazole bioisosteres.

Synthesis, structure-property relationships and pharmacokinetic evaluation of ethyl 6-aminonicotinate sulfonylureas as antagonists of the P2Y12 receptor.

The present paper describes the development of a new series of P2Y12 receptor antagonists based on our previously reported piperazinyl urea series 1 (IC50 binding affinity = 0.33 µM, aq solubility <0.1 µM, microsomal CLint (HLM) ≥300 µM/min/mg). By replacement of the urea functionality with a sulfonylurea group we observed increased affinity along with improved stability and solubility as exemplified by 47 (IC50 binding affinity = 0.042 µM, aq solubility = 90 µM, microsomal CLint (HLM) = 70 µM/min/mg). Further improvements in affinity and metabolic stability were achieved by replacing the central piperazine ring with a 3-aminoazetidine as exemplified by 3 (IC50 binding affinity = 0.0062 µM, aq solubility = 83 µM, microsomal CLint (HLM) = 28 µM/min/mg). The improved affinity observed in the in vitro binding assay also translated to the potency observed in the WPA aggregation assay (47: 19 nM and 3: 9.5 nM) and the observed in vitro ADME properties translates to the in vivo PK properties observed in rat. In addition, we found that the chemical stability of the sulfonylureas during prolonged storage in solution was related to the sulfonyl urea linker and depended on the type of solvent and the substitution pattern of the sulfonyl urea functionality.

A novel series of piperazinyl-pyridine ureas as antagonists of the purinergic P2Y12 receptor.

A novel series of P2Y(12) antagonists for development of drugs within the antiplatelet area is presented. The synthesis of the piperazinyl-pyridine urea derivatives and their structure-activity relationships (SAR) are described. Several compounds showed P2Y(12) antagonistic activities in the sub-micromolar range.

Design of small molecule inhibitors of acetyl-CoA carboxylase 1 and 2 showing reduction of hepatic malonyl-CoA levels in vivo in obese Zucker rats.

Inhibition of acetyl-CoA carboxylases has the potential for modulating long chain fatty acid biosynthesis and mitochondrial fatty acid oxidation. Hybridization of weak inhibitors of ACC2 provided a novel, moderately potent but lipophilic series. Optimization led to compounds 33 and 37, which exhibit potent inhibition of human ACC2, 10-fold selectivity over inhibition of human ACC1, good physical and in vitro ADME properties and good bioavailability. X-ray crystallography has shown this series binding in the CT-domain of ACC2 and revealed two key hydrogen bonding interactions. Both 33 and 37 lower levels of hepatic malonyl-CoA in vivo in obese Zucker rats.

Design, synthesis and biological evaluation of thrombin inhibitors based on a pyridine scaffold.

A series of 2,4-disubstituted pyridine derivatives has been designed, synthesised and evaluated as thrombin inhibitors. A Grignard exchange reaction was used to introduce various benzoyl substituents in position 4 of the pyridine ring, where they serve as P3 residues in binding to thrombin. In position 2 of the pyridine ring, a para-amidinobenzylamine moiety was incorporated as P1 residue by an SNAr reaction using ammonia as nucleophile followed by a reductive amination. A crystal structure obtained for one of the compounds in the active site of thrombin revealed that the basic amidine group of the inhibitor was anchored to Asp 189 at the bottom of the S1 pocket. A comparison with melagatran, bound in the active site of thrombin, revealed a good shape match but lack of hydrogen bonding possibilities in the S2-S3 region for the thrombin inhibitors reported in this study.

Synthesis and biological evaluation of leucine enkephalin turn mimetics.

A cyclic Leu-enkephalin mimetic containing a 7-membered ring, and two linear analogues, has been prepared on solid phase. In the cyclic mimetic the intramolecular (1-4) hydrogen bond found in crystalline Leu-enkephalin has been replaced by an ethylene bridge. In addition, the amide bond between Tyr1 and Gly2 has been replaced by a methylene ether isostere and Gly3 has been deleted. The two linear analogues both contain the methylene ether isostere instead of the Tyr1-Gly2 amide bond and the shorter of the two lacks Gly3. The three compounds, and a beta-turn mimetic analogous to the 7-membered turn mimetic but with Gly3 included, were evaluated for specific binding to micro- and delta-opioid receptors in rat brain membranes. With the exception of the beta-turn mimetic the three other Leu-enkephalin analogues all bound with varying affinity to the micro- and delta-opioid receptors. From the results it could be concluded that Leu-enkephalin binds in a turn conformation to the opiate receptors, but that this conformation is not a (1-4) beta-turn.

Synthesis and conformational studies of a beta-turn mimetic incorporated in Leu-enkephalin.

A beta-turn mimetic in which the four amino acids of a beta-turn have been replaced by a 10-membered ring has been designed, synthesized, and subjected to conformational studies. In the mimetic, the intramolecular CO(i)-HN(i)(+3) hydrogen bond that is often found in beta-turns has been replaced by an ethylene bridge. In addition, the amide bond between residues i and i + 1 was exchanged for a methylene ether isoster. Such a beta-turn mimetic, based on the first four residues of Leu-enkephalin (Tyr-Gly-Gly-Phe-Leu), was prepared in 15 steps. The synthesis relied on a beta-azido alcohol prepared in five steps from Cbz-Tyr(tBu)-OH as a key, i-position building block. tert-Butyl bromoacetate, glycine, and a Phe-Leu dipetide were then used as building blocks for positions i + 1, i + 2, and i + 3, respectively. Conformational studies based on (1)H NMR data showed that the beta-turn mimetic was flexible, but that it resembled a type-II beta-turn at low temperature. This low energy conformer closely resembled the structure determined for crystalline Leu-enkephalin.

Conformations and receptor activity of desmopressin analogues, which contain gamma-turn mimetics or a psi[CH(2)O] isostere.

Three analogues of the antidiuretic drug desmopressin ([1-desamino,8-D-arginine]vasopressin) have been prepared. In two of these, gamma-turn mimetics based on a morpholin-3-one framework have been inserted instead of residues Phe3-Asn5, whereas the third analogue has a methylene ether isostere in place of the amide bond between residues 3 and 4. The three analogues were used to probe if the structure determined for desmopressin in aqueous solution, which contains an inverse gamma-turn centered around Gln4, is important in interactions with the vasopressin V(2) receptor. Conformational studies revealed that the analogues that contain either an inverse gamma-turn mimetic or a methylene ether isostere mimicked the conformation of desmopressin fairly well and very well, respectively. Despite this, the analogues displayed only very low agonistic activities at the vasopressin V(2) receptor. Consequently, an inverse gamma-turn involving residues Phe3-Asn5 does not appear to be important when desmopressin is bound to the V(2) receptor. In addition, it was concluded that the amide bond between Phe3 and Gln4 in desmopressin is crucial for interactions with the antidiuretic V(2) receptor.

Synthesis and pharmacological evaluation of an analogue of the peptide hormone oxytocin that contains a mimetic of an inverse gamma-turn.

Oxytocin is a neurohypophyseal peptide hormone that induces labor and lactation in mammals. An inverse gamma-turn mimetic corresponding to the tripeptide Ile-Val-Asn has been synthesized and incorporated instead of residues 3-5 of oxytocin to probe the hypothesis that a gamma-turn involving these residues is found in the receptor bound conformation of oxytocin. In the turn mimetic, residues i and i + 1 are connected by a psi[CH(2)O] isostere while a covalent methylene bridge replaces the hydrogen bond that is often found between residues i and i + 2 in gamma-turns. The turn mimetic was assembled from three types of building blocks: an azido epoxide, an alpha-bromo acid, and a protected beta-amino alcohol. The oxytocin analogue did not induce contractions of the uterus nor did it inhibit oxytocin-induced contractions. It is suggested that the loss of bioactivity is mainly due to the presence of a psi[CH(2)O] isostere instead of an amide bond between residues i and i + 1 in the turn mimetic.