The synthesis of more than fifty 36-residue oligopeptide analogs of neuropeptide Y (NPY) and their affinity to human Y, and Y, receptors is described. Each amino acid of the natural sequence was replaced by L-alanine, the four alanine residues at position 12, 14, 18 and 23 were replaced by glycine. Additional residues .were exchanged to closely related ones in order to characterize the prerequisites for binding. A combination of automated single and multiple peptide synthesis using fluoren-9-ylmethoxycarbonyl/tert-butoxy strategy was applied. The purified peptides were characterized by electrospray mass spectrometry, analytical HPLC and amino acid analysis. Binding was investigated by displacement of '251-labelled neuropeptide Y from human neuroblastoma cell lines Whereas Pro2 and the integrity of the neuropeptide Y loop is important for the binding to the Y, receptor, exchanges within the C-terminal helix affect the affinity to the Y, receptor. The Cterminal pentapeptide amide is important for both receptors and probably represents the binding site. However, Arg33 and Arg35 may not be exchanged by L-alanine in the Y, system, whereas Arg35 and Tyr36 are the most susceptible residues in the Y, system. In order to distinguish between conformational effects and direct hormone/receptor interaction via the side chains of neuropeptide Y, circular dichroic studies of the alanine-containing peptides were performed and structure affinity relationships are discussed.Comparing the affinities of the neuropeptide Y analogs to Y, and Y, receptors significant differences were found for the two binding sites, which suggests a different active conformation of neuropeptide Y at the two subtypes of receptors. Using molecular dynamics calculations, two distinct conformations were identified which are in good agreement with the data obtained by structure/ affinity investigations. SK-N-MC and SMS-KAN.Neuropeptide Y (NPY) is a 36-amino-acid amide which exhibits a high similarity to the pancreatic polypeptide and peptide YY. It was isolated from pig brain and sequenced (Tatemoto) in 1982.Information about the secondary structure of pancreatic polypetptide hormones has been obtained through the work of Blundell and co-workers who performed X-ray analyses on avian (turkey) pancreatic polypeptide Wood, 1982., Glover et al., 1983). Residues 1-8 of the crystalline avian pancreatic polypeptide form a type I1 proline helix followed by a loop (residues 9-14) and an a-helical segment (residues 15-32). The four C-terminal amino acids adopt a relatively flexible loop-like conformation. Hydrophobic interactions of the proline helix and the amphiphilic ahelix lead to the hairpin structure. Comparative circular dichroic measurements of different pancreatic polypeptides and Correspondence to A. G.

Starting from the recently reported nonpeptidic angiotensin II (AII) receptor antagonists DuP753 (1) and Exp 7711 (2), we have designed and investigated novel substituted benzimidazoles. Systemic variation of several substituents at the benzimidazole ring positions 4-7 led to the finding that substitution in position 6 with acylamino groups results in highly active AII antagonists. Compounds with 6-membered lactam or sultam substituents in position 6 of benzimidazole showed receptor activities in the low nanomolar range but were only weakly active when given orally to rats. In contrast, analogous substitution of the benzimidazole moiety with basic heterocycles resulted in potent AII antagonists which were also well absorbed after oral application. The most active compound of this series, 33 (BIBR 277), was selected as a candidate for clinical development. On the basis of molecular modeling studies a binding model of this new class of AII antagonists to the AT1 receptor is proposed.

The structure-activity relationships in two series of hypoglycemic benzoic acid derivatives (5, 6) were investigated. Series 5 resulted from meglitinide (3) when the 2-methoxy was replaced by an alkyleneimino residue. Maximum activity was observed with the cis-3, 5-dimethyl-piperidino (5h) and the octamethyleneimino (5l) residues. Series 6 resulted from the meglitinide analogon 4 bearing an inversed amido function when the 2-methoxy, the 5-fluoro, and the alpha-methyl residue were replaced by a 2-piperidino, a 5-hydrogen, and a larger alpha-alkyl residue, respectively. An alkoxy residue ortho to the carboxy group further increased activity and duration of action in the rat. The most active racemic compound, 6al (R4 = isobutyl; R = ethoxy), turned out to be 12 times more active than the sulfonylurea (SU) glibenclamide (1). Activity was found to reside predominantly in the (S)-enantiomers. Compared with the SUs 1 and 2 (glimepiride), the most active enantiomer, (S)-6al (AG-EE 623 ZW; repaglinide; ED50 = 10 micro/kg po), is 25 and 18 times more active. Repaglinide turned out to be a useful therapeutic for type 2 diabetic patients; approval was granted recently by the FDA and the EMEA. From investigations on the pharmacophoric groups in compounds of type 5 and 6, it was concluded that in addition to the two already known-the acidic group (COOH; SO2NH) and the amidic spacer (CONH; NHCO)-the ortho residue R1 (alkyleneimino; alkoxy; oxo) must be regarded as a third one. A general pharmacophore model suitable for hypoglycemic benzoic acid derivatives, SUs, and sulfonamides is proposed (Figure 6). Furthermore, from superpositions of low-energy conformations (LECs) of 1, 2, and (S)-6al, it was concluded that a common binding conformation (LEC II; Figure 10B) may exist and that differences in binding to the SU receptor and in the mechanism of insulin release between repaglinide and the two SUs may be due to specific hydrophobic differences.

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