Syntheses and biological activities of atrial natriuretic polypeptide analogs

Recently several peptides with natriuretic and diuretic potencies were isolated from human and rat atrial extract, and the precursors of the peptides were sequenced. Of the peptides, -human and rat atrial natriuretic polypeptides (-hANP, -rANP), consisting of 28 amino acids, are thought to be essential to the potency and to play an important role in the blood pressure regulation system. The amino acid sequence of -hANP is different from that of -rANP only at the position 12 (isoleucine in -rANP). In the present study, we synthesized ANPs and their analogs using a new deprotection procedure based on the concept of push-pull mechanism. Using the synthetic ANP analog, we also developed a radioimmunoassay for -ANP and examined the structure-activity relationship. Synthetic -hANP caused potent, rapid, and short-acting increases in Na⁺ and Cl^– excretion, and also an increase in urine flow and K⁺ excretion of lesser magnitude, when injected into rat. Also, we synthesized a cyclic part of -hANP, -ANP(7–23)-NH₂. Since this peptide had a little diuretic and natriuretic potency, we attempted to synthesize a chemically stable -hANP analog. We considered that the disulfide bond would be equivalent to propylene with regard to interatomic distance and employed 8-aminocaprylic acid instead of cystine. This cyclic peptide, named cyclonatrin-54, had a somewhat higher potency than -hANP(7–23)-NH₂ for diuresis and natriuresis, as expected. Furthermore, using a synthetic intermediate of cyclonatrin-54, we prepared a linear ANP analog, -hANP(8–22), Phe-Gly-Gly-Arg-Met-Asp-Arg-Ile-Gly-Ala-Gln-Ser-Gly-Leu-Gly. This linear 15-amino acid peptide had a dose-dependent natriuretic and diuretic activity, but no hypotensive effect. It was surprising that a linear peptide exhibited a potent natriuretic activity. For the first time, a linear peptide has been prepared that has substantial natriuretic and diuretic potency. We synthesized some analogs of this 15-amino acid peptide and investigated the structure-activity relationship.This article was presented during the proceedings of the International Conference on Macromolecular Structure and Function, held at the National Defence Medical College, Tokorozawa, Japan, December 1985.     

Syntheses and biological activities of sandostatin analogs containing stereochemical changes in positions 6 or 8

In a continuation of our research efforts on the design and synthesis of novel peptidomimetic structures, we have synthesized a series of sandostatin amide analogs in which stereoisomers of threonine and beta-hydroxyvaline(beta-Hyv) are employed. The analogs D-Phe1-c[Cys2-Phe3-D-Trp4-Lys5-Xaa6-Cys 7]-Xbb8-NH2 (Xaa = allo-Thr, D-allo-Thr, D-beta-Hyv, beta-Hyv, D-Thr, and Xbb = Thr or Xaa = Thr and Xbb = allo-Thr, D-allo-Thr, beta-Hyv, D-Thr) explore the effects on biological activity of stereochemical modifications and beta-methylation at positions 6 or 8. By these modifications, we examine the role of the two residues in binding to somatostatin receptors. We describe the synthesis and biological activity of these analogs. In combination with the results of the conformational analysis, this study provides new insights into the structural requirements for the binding affinity of somatostatin amide analogs to somatostatin receptors [Mattern et al., Conformational analyses of sandostatin analogs containing stereochemical changes in positions 6 or 8].     

Studies of peptide antibiotics. XLIV. Syntheses and biological activities of gramicidin S analogs containing delta-hydroxy-L-norvaline or glycine

The antibiotic gramicidin S (GS) has the structure of cyclo (-L-Val1-L-Orn2-L-Leu3-D-Phe4-L-Pro5-L-Val1'-L-Orn2'-L-Leu3'-D-Phe4'-L-Pro5'-) and is basic in character. Five GS analogs including [Gly1,1']-GS and the neutral [L-Hnv2,2']-GS (Hnv represents delta-hydroxynorvaline) were synthesized by the solid-phase method to evaluate the role of L-Val1,1' and L-Orn2,2' residues in GS. The hybrid analogs [( Gly1]-GS and [L-Hnv2]-GS) and [D-Tyr4,4']-GS showed high antibacterial activities, whereas [Gly1,1']-GS and [L-Hnv2,2']-GS possessed no activity. Inhibitory effects by these analogs for the adsorption of 14C-labeled GS on cells of bacteria sensitive to GS were determined. The structure-activity relationship of GS is discussed on the basis of the results on these GS analogs.     

Syntheses and biological activities of deoxy-d-allose fatty acid ester analogs

We describe the syntheses of three different deoxy-D-allose analogs [2-deoxy-D-allose (2-DOAll), 1,2-dideoxy-D-allose (1,2-DOAll), and 1,2-didehydro-1,2-dideoxy-D-allose (1,2-DHAll)] and their fatty acid esters via regioselective lipase-catalyzed transesterification. Among them, 2-DOAll and its decanoate (2-DOAll-C10) showed higher inhibitory activity on plant growth, which is similar to D-allose (All) and its decanoate (All-C10). Bioassay results of deoxy-All-C10 on four plant species suggest that the hydroxy group at the C-1 position might be important showing growth inhibitory activity. In addition, co-addition of gibberellin (GA₃) with 1,2-DHAll-C10 and 2-DOAll-C10 recovered plant growth, suggesting that they might mainly inhibit biosynthesis of gibberellin.     

Syntheses and biological activities of daunorubicin analogs with uncommon sugars

To study the effects of the sugar structure on the activity of anthracycline against cancer cells, six daunorubicin analogs containing different uncommon sugars were synthesized. Their cytotoxicities were tested against colon cancer cells by MTS assay. The results showed that the aglycon without sugar moiety has 70-100-fold lower activity against cancer cells than daunorubicin derivatives with various uncommon sugars. It suggests that the sugar structure in daunorubicin plays a critical role in determining its anticancer activity. In the compounds with various sugars, the 4'-OH of the sugar is an important determinant for their activity, while the axial-3'-substituent in the sugar interferes with the binding of daunorubicins to DNA. Therefore, 2,6-dideoxy sugars are a better choice for generating biologically active daunorubicin analogs than 6-deoxysugars, 2,3,6-trideoxysugars, or 2,3,4,6-tetradeoxysugars.     

Cyclic enkephalin analogs containing a cystine bridge

Two conformationally constrained enkephalin analogs were synthesized by substitution of cysteines in positions 2 and 5 and oxidative disulfide bond formation. In the guinea pig ileum assay the obtained cyclic analogs, [D-Cys²-L-Cys⁵]enkephalinamide and [D-Cys²-D-Cys⁵]enkephalinamide, showed potency ratios of 37.9 ± 0.8 and 73.3 ± 0.9, respectively, relative to [Met⁵]enkephalin. The extremely high potency of the analogs was shown to be a consequence of the conformational restrictions introduced by cyclization. Rat brain membrane binding studies with [³H]naloxone and [³H](D-Ala², D-Leu⁵)enkephalin as radiolabels revealed a moderate preference of both analogs for μ-receptors over δ-receptors. Furthermore, the cystine-containing analogs were shown to be highly resistant to enzymatic degradation.     

Synthesis of novel sulfonamide analogs containing sulfamerazine/sulfaguanidine and their biological activities

Sulfamerazine and sulfaguanidine are clenched with p-nitrobenzoyl chloride and the products obtained are reduced to Na_xS in ethanol–water. Novel sulfonamides (6a–g and 9a–g) were synthesized by the reaction of these reduced products (4 and 8) with various sulfonyl chlorides (5a–g). The structures of these compounds were characterized using spectroscopic analysis (IR, ¹H-NMR, ¹³C-NMR and HRMS) technique. Antimicrobial activity of sulfonamides (3, 4, 7, 8, 6a–g and 9a–g) was evaluated by the agar diffusion method. These compounds showed antimicrobial activity against tested microorganism strains (Gram-positive bacteria, clinic isolate and yeast and mold). Compounds 9d, 9e, 9a, 6d and 6e showed particularly antimicrobial activity against tested Gram-positive (Bacillus cereus and B. subtilis) and Gram-negative (Enterobacter aerogenes) bacteria.     

Conformation of cyclic analogs of enkephalin. II. Analogs containing a cystine bridge

A systematic survey has been made, using molecular mechanics, of the conformation of the ring entity of the enkephalin analogs, [D -Cys²-L -Cys⁵]-enkephalinamide and [D -Cys²-D -Cys⁵]enkephalinamide. These molecules are considerably more flexible than the analog Tyr-cyclo(N^γ-D -A₂bu-Gly-Phe-Leu-), but the favored conformations of all three are very similar. The results of these studies are compatible with a Gly³-Phe⁴ type II′ bend in the active conformation of enkephalin.     

Design, synthesis and biological activities of thiourea containing sorafenib analogs as antitumor agents

A novel series of diaryl thiourea containing sorafenib derivatives 9a-t was designed and synthesized. The structures of all the newly synthesized compounds were determined by (1)H NMR, (13)C NMR and HRMS. Their antiproliferative activities against HCT116 and MDA-MB-231 cell lines, and their inhibitory activities against the phosphorylation of VEGFR were evaluated and described. Some of the compounds showed significant activities against both cell lines and VEGFR. Compounds 9g, 9m, 9o and 9p demonstrated competitive antiproliferative activities to sorafenib, the reference standard, while compounds 9d, 9m, and 9p showed significant inhibitory activities against the phosphorylation of VEGFR.     

Syntheses and biological evaluation of ring-C modified colchicine analogs

Ring-C modified alkaloids were synthesized from colchicine using iminonitroso Diels–Alder reactions in a highly regio- and stereoselective fashion. Several analogs exhibited cytotoxic activity similar to that of colchicine itself against PC-3 and MCF-7 cancer cell lines, by serving as prodrugs of colchicine through retro Diels–Alder reactions under the assayed conditions. In vitro microtubule polymerization assays indicated that these modifications affected their interaction with tubulin.     

Syntheses and biological activities of pyranyl-substituted cinnamates

Twenty-two kinds of pyranyl-substituted cinnamates were synthesized by the reaction of 4-hydroxy-6-(2-phenylethyl)-2H-pyran-2-one or 4-hydroxy-6-methyl-2H-pyran-2-one (HMP) with a variety of substituted cinnamic acids, and their antifungal and plant growth inhibitory activities were investigated. Among the compounds prepared, 6-methyl-2-oxo-2H-pyran-4-yl 3-(4-isopropylphenyl)propenoate (H5) showed the strongest antifungal activity against Rhizoctonia solani and Sclerotium dellfinii, and 6-methyl-2-oxo-2H-pyran-4-yl 3-(2-methylphenyl)propenoate (H2) had the highest plant growth inhibitory activity toward Brassica rapa.     

Syntheses and biological activities of potent bombesin receptor antagonists.

Bombesin receptor antagonists are potential therapeutic agents due to their ability to act as inhibitors of cellular proliferation. On the basis of our hypothesis concerning the mechanism of action of gastrin associating an activating enzyme to the receptor and on the results reported in the literature, we have synthesized bombesin analogs which have been modified in the C-terminal part. Potent bombesin receptor antagonists were obtained by replacement of Leu-13 with a statyl residue or with a residue bearing an hydroxyl group in place of the carbonyl function of Leu-13. Several inhibitors were able to recognize the bombesin receptor on rat pancreatic acini and antagonized bombesin stimulated amylase secretion in the nanomolar range. These compounds were also able to recognize the bombesin receptor and to inhibit [3H] thymidine incorporation in 3T3 cells with the same potency.     

Immunological and biological activities of fragments and analogs of bradykinin.

Using a number of analogs and fragments of a short-chain peptide bradykinin, a series of experiments have been carried out to assess the effect of modifications to the basic structure of the parent molecule on its myotropic and immunoreactive properties. Binding kinetics of both an antibody raised against the authentic nonapeptide and its specific biological receptor found in the guinea pig ileum were used to study these alteration effects. Peptide derivatives of bradykinin with an extension at the N-terminal (Lys- and Met-Lys-bradykinin) cross-react with the antibody raised to bradykinin 59 and 70% respectively. On the other hand, internal fragments with intact C-termini (2-9 and 3-9 bradykinin) react with this same antibody to an extent of 250 and 875% respectively, indicating that they are more potent antigens than the vasopressor molecule itself. Other internal fragments, as well as 9-substituted analogs effectively and not interact. These results indicated that the C terminal arginine of bradykinin is indeed essential in the binding mechanism with its antibody. This in turn illustrates the role of the carrier ovalbumin in the development of antiserum to the ovalbumin-toluene-diisocyanate-bradykinin complex. The physiological experiments with the guinea pig bioassay preparations lead to similar conclusions. Most internal fragments of bradykinin are devoid of activity, whereas N-terminal fragments (2-9, 3-9, and 5-9 bradykinin) have retained some activity again indicating a need for an intact arginine residue at the C-terminus of the molecule. Any modification in position 9 results in severe impairment of biological activity. Thus, the C-terminal residue of bradykinin must be conserved in order that the molecule may retain its immunological and physiological activities. Any extensions, deletions, or modifications of this site will severely retard these functions.     

Syntheses and biological activities of azido ubiquinone derivatives

A general method for the synthesis of azido-ubiquinone derivatives has been developed directly by substituting one hydrogen atom on the benzoquinone ring with an azido group under weakly acidic conditions. The reaction takes several hours and the yield is generally low. The azido-ubiquinone was purified by preparative thin layer chromatography, and identified by NMR, IR and mass spectra. All the synthesized azido-ubiquinone derivatives show partial activity in mediating biological electron transfer in the dark, and show partial or complete inhibition upon photolysis.