Dehydrophenylalanyl analogs of bradykinin: Synthesis and biological activities

We have synthesized three analogs of the potent vasodilator peptide bradykinin, ArgProProGlyPhe SerProPheArg (BK), containing dehydrophenylalanine (Δ^zPhe) in place of the phenylalanyl residues at positions 5 and/or 8. The analogs, [Δ^zPhe⁵]BK, [Δ^zPhe⁸]BK, and [Δ^zPhe^5,8]BK, were assayed for their effects on isolated smooth muscle tissues and on the systemic arterial blood pressure of rats. In these assays [Δ^zPhe⁵]BK showed considerably high biological activities, particularly in terms of its blood pressure-lowering effects, being over 23 times more potent than BK when given intravenously. [Δ^zPhe⁸]BK was less potent than BK and [Δ^zPhe^5,8]BK had effects comparable to those of BK. All three synthetic analogs appear to be more resistant than BK to enzymic degradation during passage through the pulmonary vascular bed.     

Synthesis, biological activity and conformation of enkephalin analogs structurally related to kyotorphin

[D-Arg2,Leu5]Enkephalin and two series of its N-terminal short-chain analogues with a free and modified C-terminal carboxylic group, viz. amides and ethyl esters of tri- and tetrapeptides, were synthesized in solution and by solid-phase method. Their analgesic activity, assayed by the "tail pinch" method following intracisternal and intravenous administration to mice, was compared with activity of enkephalins and morphine. To study the space structure of the synthesized compounds, conformational calculations and fluorescence spectroscopy were applied to measure distance between aromatic nuclei of tyrosine and phenylalanine residues in the two tetrapeptides. Ethyl esters of the tri- and tetrapeptides exceed in analgesic activity the corresponding carboxylic acids and amides. In contrast to the pentapeptide, the tetrapeptide analogues were active upon intravenous administration. Conformational aspects of this series of analogues are discussed in detail; the abrupt increase in activity upon transition from tri- to tetrapeptides does not appear to be related to conformational changes.     

Synthesis,conformation, and antiviral activity of 5-methoxymethyl-2'-deoxycytidine analogs

Analogs of 5-methoxymethyl-2'-deoxycytidine, MMdCyd (1) by substitution at N4 were synthesized to impart resistance against deamination. The anti HSV-1 activity and solution conformation of analogs were determined. N4-Butanoyl-MMdCyd (10) was a potent inhibitor of HSV-1 replication while N4-hexanoyl-MMdCyd (11), N4-propanoyl-MMdCyd (9) and N4-acetyl-MMdCyd (8) had good activity against HSV-1 replication. All other analogs were devoid of activity against HSV-1.     

Synthesis, conformation, and biological activity of the carbohydrate-free vespulakinin 1

Synthesis of the carbohydrate-free heptadecapeptide corresponding to the amino acid sequence of vespulakinin 1 was achieved by the continuous flow solid phase procedure on 4-hydroxymethyl-phenoxyacetyl-norleucyl derivatized Kieselguhr-supported polydimethylacrylamide resin, as well as by a combination of solid phase and solution syntheses. Preformed Fmoc-amino acid symmetrical anhydrides (Boc derivative for the N-terminal residue) were used for amine acylation in the continuous flow method. Serine and threonine were side chain protected as tert.-butyl ethers and the 4-methoxy-2, 3, 6,-trimethyl-benzenesulfonyl group was used for masking the guanidino function of arginine residues. After cleavage from the resin the final peptide was purified by ion exchange chromatography and characterized by amino acid analysis, high voltage electrophoresis, and RP-HPLC analysis. Alternatively, the protected N-terminal octapeptide, Fmoc-Thr(But)-Ala-Thr(But)-Thr(But)-Arg(Mtr)-Arg-(Mtr)-Arg(Mtr)-Gly-OH was prepared on 4-hydroxymethyl-3-methoxyphenoxyacetyl-norleucyl derivatized Kieselguhr-supported polydimethylacrylamide resin and the C-terminal nonapeptide H-Arg(NO2)-Pro-Pro-Gly-Phe-Ser-Pro-Phe-Arg-(NO2)-OBzl was synthesized in solution through the fragment condensation method. The two fragments were coupled by the DCC-HOBt procedure and the resulting heptadecapeptide was deblocked and purified. The conformational features of the synthesized peptides are reported. Preliminary pharmacological experiments indicated that carbohydrate-free vespulakinin 1 is more potent than bradykinin in lowering rat blood pressure.     

Synthesis, biological activity and conformational analysis of cyclic GRF analogs

A novel cyclic GRF analog, cyclo(Asp8-Lys12)-[Asp8,Ala15]-GRF(1-29)-NH2, i.e. cyclo8,12[Asp8,Ala15]-GRF(1-29)-NH2, was synthesized by the solid phase procedure and found to retain significant biological activity. Solid phase cyclization of Asp8 to Lys12 proceeded rapidly (approximately 2 h) using the BOP reagent. Substitution of Ala2 with D-Ala2 and/or NH2-terminal replacement (desNH2-Tyr1 or N-MeTyr1) in the cyclo8,12[Asp8,Ala15]-GRF(1-29)-NH2 system resulted in highly potent analogs that were also active in vivo. Conformational analysis (circular dichroism and molecular dynamics calculations based on NOE-derived distance constraints) demonstrated that cyclo8,12[Asp8,Ala15]-GRF(1-29)-NH2 contains a long alpha-helical segment even in aqueous solution. A series of cyclo8,12 stereoisomers containing D-Asp8 and/or D-Lys12 were prepared and also found to be highly potent and to retain significant alpha-helical conformation. The high biological activity of cyclo8,12[N-MeTyr1,D-Ala2,Asp8,Ala15]-GRF(1-29)- NH2 may be explained on the basis of retention of a preferred bioactive conformation.     

Isosteric analogs of lenalidomide and pomalidomide: Synthesis and biological activity

A series of analogs of the immunomodulary drugs lenalidomide (1) and pomalidomide (2), in which the amino group is replaced with various isosteres, was prepared and assayed for immunomodulatory activity and activity against cancer cell lines. The 4-methyl and 4-chloro analogs 4 and 15, respectively, displayed potent inhibition of tumor necrosis factor-α (TNF-α) in LPS-stimulated hPBMC, potent stimulation of IL-2 in a human T cell co-stimulation assay, and anti-proliferative activity against the Namalwa lymphoma cell line. Both of these analogs displayed oral bioavailability in rat.     

Antiplasmodial activity of hydroxyethylamine analogs: Synthesis,biological activity and structure activity relationship of plasmepsin inhibitors

Malaria, particularly in endemic countries remains a threat to the human health and is the leading the cause of mortality in the tropical and sub-tropical areas. Herein, we explored new C₂ symmetric hydroxyethylamine analogs as the potential inhibitors of Plasmodium falciparum (P. falciparum; 3D7) in in-vitro cultures. All the listed compounds were also evaluated against crucial drug targets, plasmepsin II (Plm II) and IV (Plm IV), enzymes found in the digestive vacuole of the P. falciparum. Analog 10f showed inhibitory activities against both the enzymes Plm II and Plm IV (K_i, 1.93?±?0.29?µM for Plm II; K_i, 1.99?±?0.05?µM for Plm IV). Among all these analogs, compounds 10g selectively inhibited the activity of Plm IV (K_i, 0.84?±?0.08?µM). In the in vitro screening assay, the growth inhibition of P. falciparum by both the analogs (IC₅₀, 2.27?±?0.95?µM for 10f; IC₅₀, 3.11?±?0.65?µM for 10g) displayed marked killing effect. A significant growth inhibition of the P. falciparum was displayed by analog 12c with IC₅₀ value of 1.35?±?0.85?µM, however, it did not show inhibitory activity against either Plms. The hemolytic assay suggested that the active compounds selectively inhibit the growth of the parasite. Further, potent analogs (10f and 12c) were evaluated for their cytotoxicity towards mammalian HepG2 and vero cells. The selectivity index (SI) values were noticed greater than 10 for both the analogs that suggested their poor toxicity. The present study indicates these analogs as putative lead structures and could serve as crucial for the development of new drug molecules.     

Synthesis and biological activity of cyclic analogs of angiotensin

Biological properties of five novel angiotensin analogues synthesized, using the conventional methods of peptide chemistry, have been studied. Cyclization was attained by means of amide linkage with the aid of diphenylphosphorylazide or pentafluorophenyl esters. Unlike the natural hormone, the cyclic analogues of angiotensin show no pressor activity, but elicit a depressor effect untypical of angiotensin. A slight pressor activity was exhibited by the compound containing aspartic acid in position 1. The cyclic analogues in question release histamine from peritoneal mast cells in rats.     

CD-n.m.r. study of the solution conformation of bradykinin analogs containing alpha-aminoisobutyric acid

The conformation in aqueous solution of several alpha-aminoisobutyric acid (AIB)-containing analogs of bradykinin (BK) has been probed by complementary CD and 1H n.m.r. measurements. The conclusion reached is that substitution of AIB for Pro2 and/or Pro3 in BK stabilizes a degree of beta-turn conformation in the N-terminal tetrapeptide moiety of the resulting analogs. Changing the solvent from water to DMSO or TFE further enhances the contribution of particular hydrogen bonded structures to the time-averaged conformation of these peptides. Bradykinin and [AIB7]-BK adopt similar hydrogen bonded conformations in TFE, apparently with a contribution from a beta-turn involving their common Arg1-Pro2-Pro3-Gly4 moiety. The contrasting biological activities of BK and its AIB-analogs are considered in terms of the conformational analogy between the AIB-residue and cis' Pro and the propensity for a beta-turn at the N-terminus of the peptide.     

Modified chemotactic peptides: Synthesis,conformation, and biological activity of for-Thp-Leu-ΔzPhe-OMe

For-Thp-Leu-Δ^zPhe-OMe ( 2 ), an analogue of the chemotactic tripeptide For-Met-Leu-Phe-OMe, containing 4-aminotetrahydrothiopyran-4-carboxylic acid (Thp) and (Z)-2,3-didehydrophenylalanine (Δ^zPhe) as achiral, conformationally restricted mimics of Met and Phe, respectively, has been synthesized. In the crystal the new formyltripeptide adopts a type I β-turn conformation stabilized by a weak H bond between the formylic oxygen and the Δ^zPhe NH. ¹H-nmr analysis based on NH solvent accessibility and nuclear Overhauser effect experiments suggests that the β-turn is not preferred in CDCl₃ solution where a γ-turn, centered at the Thp residue, prevails. The biological activity of 2 has been determined on human neutrophils and compared to that of previously studied analogues. The tripeptide 2 is practically unable to elicit superoxide anion production and lysozyme release, while slight, but not statistically significant activity was induced in chemotaxis. The role of the orientation of the aromatic ring with respect to the backbone adjacent atoms is discussed. © 1994 John Wiley & Sons, Inc.     

Synthesis,conformation and biological activity of centrally modified pseudopeptidic analogues of For-Met-Leu-Phe-OMe

Summary. For-Met-βAlaψ[CSNH]-Phe-OMe (3), For-Met-βAlaψ[CH₂NH]-Phe-OMe (5), For-Met-NH-pC₆H₄-SO₂-Phe-OMe (8a), For-Met-NH-mC₆H₄-SO₂-Phe-OMe (8b) and the corresponding N-Boc precursors (2, 4, 7a, b) have been synthesized and their activity towards human neutrophils has been evaluated in comparison with that shown by the reference tripeptide For-Met-Leu-Phe-OMe (fMLF-OMe). Chemotaxis, lysozyme release and superoxide anion production have been measured. ¹H NMR titration experiments and IR spectra have been discussed in order to ascertain the preferred solution conformation adopted by the tripeptide 3 with particular reference to the presence of a folded conformation centred at the centrally positioned thionated β-residue.     

Synthesis and biological activity of N-methylated analogs of endomorphin-2

In this paper, we describe the synthesis of a series of endomorphin-2 analogs containing N-methylated amino acids, consecutively in each position. The μ-opioid receptor binding affinities of the new analogs were determined in the displacement experiments. Their in vivo antinociceptive activity was assessed in the hot-plate test in mice after central (icv) and peripheral (ip) administration. [Sar²]endomorphin-2, which had the highest μ-receptor affinity, also showed the strongest analgesic effect when administered centrally and was the only analog that retained activity after peripheral injection.     

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.     

Synthesis and biological activity of nucleoside antibiotics, ascamycin and its amino acid analogs

Synthesis of an alanylsulfamoyl nucleoside antibiotic, ascamycin was achieved by the condensation of N6-t-butyloxycarbonyl-2-chloro-9-(2',3'-O-isopropylidene-5'-O-sulfamoyl- beta-D- ribofuranosyl)adenine(3) with t-butyloxycarbonyl-L-alanylimidazole in the presence of NaH in DMF. Deprotection with 90% trifluoroacetic acid gave ascamycin in 61% overall yield. This procedure may be applicable for preparation of a number of amino acid analogs of ascamycin.     

Synthesis of desthio prenylcysteine analogs: sulfur is important for biological activity

N-Acetyl-S-farnesyl cysteine (AFC) is the minimal synthetic substrate for the enzyme Icmt, which methylates prenylated proteins. The desthio-AFC isostere 2 has been synthesized in racemic form. This analog was not an Icmt substrate, but instead a weak inhibitor with an IC50 of approximately 325 microM.     

Synthesis and biological activity of position 1 analogs of LH-RH.

(Formyl-sarcosine)1-LH-RH (I), (acetyl-sarcosine)1-LH-RH (II), (2-pyrrolidone-4-carboxylic acid)1-LH-RH (III), (N-methyl-2-pyrrolidone-4-carboxylic acid)1-LH-RH (IV, hydroxyproline1-LH-RH (V) and (cylcopentane-carboxylic acid)1-LH-RH (VI) were synthesized by solid phase methods on a benzhydrylamine resin support. Peptides I-IV were assayed for LH- and FSH-releasing activity over a 4-h period after subcutaneous infection into immature male rats in order to detect any prolongation ofactivity. The peptides were found to have the following integrated LH-releasing activities compared with LH-RH: I, 64%; II, 72%; III, 19%; IV, 58%. None of the peptides were found to be longer acting than LH-RH. Peptides V and VI were far less active, 0.001% and 1.4%, respectively.     

Synthesis and biological activity of five -Cys analogs of human insulin

Five analogs of human insulin with -Cys in different positions (A⁶, A⁷, A¹¹, A⁶⁺¹¹, B⁷) have been synthesized by the fragment condensation approach, combined with selective disulfide formation. All of them have physicochemical properties noticeably different from those of human insulin. They possess very low biological activity (0.03−1.2%, glucose oxidation in rat fat cells). In contrast, the potency for antibody binding ranges from 7 to 70% of that of insulin. The two analogs with -Cys in positions A⁶ and A⁷ have been obtained in crystalline form.