Stimulation of rat uterine collagen synthesis by relaxin

Immature, ovariectomized, estrogen-primed rats respond to the administration of porcine relaxin by an increase in the incorporation of labeled amino acids ([14C]leucine, [14C]phenylalanine, [3H]proline) into uterine proteins in vitro. The maximum response occurs about 12 hr after a single injection of 0.1 mg relaxin in benzopurpurine 4B solution; subsequently, the relaxin effect declines but is still apparent after 24 hr. Smaller, but still significant increases in incorporation rates can be induced by relaxin in the absence of estrogen priming. Uterine collagen synthesis, as indicated by the incorporation of [3H]proline and its conversion to hydroxyproline, appears to be a primary target of the relaxin stimulus, since the effect of relaxin upon proline incorporation into uterine collagen is significantly greater than its effect upon labeling of noncollagen protein.     

Extending the concept of template-assembled synthetic proteins.

The creation of native-like macromolecules in copying nature's way represents a fascinating challenge in protein chemistry today. In the absence of a detailed knowledge of the complex folding pathway the ultimate goal in protein de novo design, the construction of artificial proteins with predetermined three-dimensional structure and tailor-made functions based on a defined, generally valid set of rules, appears to be still out of reach. With progress in synthesis strategies and biostructural characterization methods, topological templates have become a versatile tool for inducing and stabilizing secondary and tertiary structures, such as protein loops, beta-turns, alpha-helices, beta-sheets and a variety of folding motifs. In this article, we extend the concept of template-assembled synthetic proteins for the construction of protein-like topologies with multiply bridged, oligocyclic chain architectures termed locked-in tertiary folds that exhibit unique physicochemical and folding properties because of the highly confined conformational space. Furthermore, we show that some fundamental questions in protein assembly can be approached applying the template concept. Using covalent template trapping of self-associated peptide assemblies in aqueous solution the structural and physical forces guiding protein folding, supramolecular assembly and molecular recognition processes can be studied on a molecular level.     

Novel synthesis of new pyrazole thioglycosides as pyrazomycin analogues

This study reports a novel method for the synthesis of a new class of pyrazole thioglycosides 7a-h as pyrazomycin analogues. These series of compounds were designed through the reaction of sodium 2-cyano-3-oxo-3-(4-substitutedphenylamino)prop-1-ene-1,1-bis(thiolate) salts 2 with phenyl hydrazine in ethanol at room temperature to give the corresponding sodium 5-amino-4-(substitutedphenylcarbamoyl)-1-phenyl-1H-pyrazole-3-thiolates 3a-d. The latter compounds were treated with tetra-acetylated glycosyl bromides 4a,b in DMF at ambient temperature to give the corresponding pyrazole thioglycosides 6a-h. Treatment of pyrazole salts 3a–d with hydrochloric acid at room temperature afforded the corresponding 3-mercaptopyrazole derivatives 5. The latter compounds were treated with tetra-acetylated glycosyl bromides 4 in sodium hydride-DMF to tolerate the S-glycosyl 6a-h compounds. Ammonolysis of the latters afforded the corresponding free thioglycosides 7a-h. The structures of the reaction products were elucidated based on spectral data and elemental analysis.     

Total synthesis of human relaxin and human relaxin derivatives by solid-phase peptide synthesis and site-directed chain combination

Human relaxin, a two-chain protein hormone, was synthesized by solid-phase peptide synthesis in combination with a novel thiol-protecting group strategy whereby the three disulfide bonds could be synthesized sequentially and without error. The final product was shown to be homogeneous by reversed-phase high performance liquid chromatography and electrophoresis and had the correct amino acid composition and sequence. Tryptic digestion and peptide mapping of the synthetic relaxin by reversed-phase high performance liquid chromatography resulted in a pattern identical with that produced by standard tryptic relaxin fragments synthetized by different methods. Three human relaxin derivatives containing oxidized methionine, formyltryptophan, and bis[B13,B17-citrulline]-relaxin, were produced and their biological activity and structural similarity to human relaxin was assessed. All derivatives, except those containing modified tryptophan residues, showed indistinguishable circular dichroic spectra, indicating that the modifications did not cause significant structural changes. However, only human relaxin and the tryptophan- and methionine-protected relaxin derivatives showed bioactivity. The derivative in which the two arginines in positions B13 and B17 had been replaced by the uncharged isosteric amino acid citrulline were biologically inactive. This observation confirms preliminary studies (Büllesbach, E. E. and Schwabe, C. (1988) Int. J. Pept. Protein Res. 32, 361-367) that suggested that these two conserved arginines located in the midregion of the relaxin B chain are essential for the function of the hormone.     

Novel C-4 heteroaromatic kainoid analogues: a parallel synthesis approach

New C-4 thiazole 4, 5 and aminothiazole 6, 7 kainoid analogues were efficiently synthesised in five steps from commercially available (-)-alpha-kainic acid I and exhibited strong binding to the kainate receptors. A reactive alpha-bromoketone 10 was generated and reacted with thioamides and thioureas to form thiazole and aminothiazole heterocycles 11-14. Deprotection gave the new kainoid amino acids 4-7 in excellent yield.     

Improved chemical synthesis and demonstration of the relaxin receptor binding affinity and biological activity of mouse relaxin

The primary stored and circulating form of relaxin in humans, human gene-2 (H2) relaxin, has potent antifibrotic properties with rapidly occurring efficacy. However, when administered to experimental models of fibrosis, H2 relaxin can only be applied over short-term (2-4 week) periods, due to rodents mounting an antibody response to the exogenous human relaxin, resulting in delayed clearance and, hence, increased and variable circulating levels. To overcome this problem, the current study investigated the therapeutic potential of mouse relaxin over long-term exposure in vivo. Mouse relaxin is unique among the known relaxins in that it possesses an extra residue within the C-terminal region of its A-chain. To enable a detailed assessment of its receptor interaction and biological properties, it was chemically synthesized in good overall yield by the separate preparation of each of its A- and B-chains followed by regioselective formation of each of the intramolecular and two intermolecular disulfide bonds. Murine relaxin was shown to bind with high affinity to the human, mouse, and rat RXFP1 (primary relaxin) receptor but with a slightly lower affinity to that of H2 relaxin. When administered to relaxin-deficient mice (which undergo an age-dependent progression of organ fibrosis) over a 4 month treatment period, mouse relaxin was able to significantly inhibit the progression of collagen accumulation in several organs including the lung, kidney, testis, and skin (all p < 0.05 vs untreated group), consistent with the actions of H2 relaxin. These combined data demonstrate that mouse relaxin can effectively inhibit collagen deposition and accumulation (fibrosis) over long-term treatment periods.     

Effects of endothelin and relaxin on rat uterine segment contractility.

In order to determine the effects of endothelin (ET) and relaxin on uterine contractility, immature female rats were treated with estrogen (E, 1 microgram s.c., Days 1-3) or estrogen and progesterone (2 mg s.c. [E + P], Days 2 and 3), and killed; the uterine horns were removed and suspended in muscle baths. Initially, we determined the contractile response to varying doses of ET and how this response was altered by pretreatment with progesterone. Uterine strips from animals treated with E + P (n = 10) were less sensitive to the stimulatory effects of ET than were strips from E-treated animals (n = 10). This difference was significant at ET doses above 2.5 nM. After completion of the dose-response studies, contractile patterns in response to ET and relaxin were then studied in animals treated with E (n = 10) or E + P (n = 9). ET (5 nM) significantly increased uterine contractility, mostly through an effect on the frequency of contractions (p less than 0.01). Relaxin (25 ng/ml) decreased contractility, affecting all contractile parameters measured (p less than 0.01). ET stimulated contractility in uterine horn segments previously inhibited by relaxin (p less than 0.01), and relaxin reduced the increased contractility produced by earlier exposure to ET (p less than 0.01). These data indicate that ET and relaxin can interact reversibly to control contractility in uterine horn segments in vitro, and that progesterone pretreatment can diminish the contractile response to the stimulatory effects of ET.     

Development of an efficient strategy for the synthesis of the ETB receptor antagonist BQ-788 and some related analogues

BQ-788 [N-cis-2,6-dimethylpiperidine-1-carbonyl-L-gamma-methylleucyl-D-1-methoxycarbonyltryptophanyl-D-norleucine sodium salt] is a very potent and selective ETB receptor antagonist. The formation of the highly hindered trisubstituted urea functionality in the peptide chain and the carbamination on the indole nitrogen of the tryptophan side chain are major challenges in the synthesis of this particular antagonist. Furthermore, the high cost of the unnatural amino acids in the sequence of BQ-788 and its reported synthesis render this pseudopeptide very expensive to produce. In order to improve the yield and to reduce the number of steps compared to previous reported syntheses, we developed an efficient strategy involving a novel one-pot procedure for the synthesis of a highly hindered trisubstituted urea. Under very mild conditions, the urea was obtained by using triphosgene and sodium iodide. This strategy allowed us to synthesize BQ-788 in seven steps with an overall yield of 53%. We also generalized the use of this powerful methodology by creating some new structural analogues of the cis-2,6-dimethylpiperidine moiety by replacing it with other bulky secondary amines. We evaluated the antagonist properties of those three new analogues of BQ-788 in two bioassays in vitro. These new antagonists were less potent than BQ-788 in an ETB rich preparation and inactive in an ETA rich preparation.     

The enzymatic synthesis of ATP analogues.

The enzymatic synthesis of selected adenosine 5′-triphosphate analogues from their respective 5′-monosphosphates has been achieved using phosphoenolpyruvate synthetase. Adenosine 5′-monophosphate analogues altered at positions 1,6,7,8 or 9 of the purine ring, or at the ribose 2′- or 3′-positions are substrates with 30% conversion to the nucleoside 5′-triphosphate.     

Total synthesis of epothilone E and related side-chain modified analogues via a Stille coupling based strategy.

A Stille coupling strategy has been utilized to complete a total synthesis of epothilone E from vinyl iodide 7 and thiazole-stannane 8h. The central core fragment 7 and its trans-isomer 11 were prepared from triene 15 using ring-closing metathesis (RCM), and were subsequently coupled to a variety of alternative stannanes to provide a library of epothilone analogues 18a-o and 19a-o. The Stille coupling approach was then used to prepare epothilone B analogues from the key macrolactone intermediate 24 which was itself synthesized by a macrolactonization based strategy.     

Target tissues for relaxin identified in vitro with 125I-labelled porcine relaxin.

Various tissues from the mouse, rat and guinea-pig were used to examine the binding of a biologically active, esterified and 125I-labelled porcine relaxin. Binding to mouse symphysial homogenates was time- and temperature-dependent. Other peptide hormones did not complete with relaxin for binding. Mouse uterine tissue displayed similar binding characteristics. Fractionated mammary tissue from 15- and 20-day-pregnant rats exhibited significant relaxin binding activity, as did homogenates of the guinea-pig public symphysis and cervix. Under the conditions used, no relaxin receptors were noted in the liver, spleen or heart from any of the species investigated.     

Novel analogues of neuropeptide Y with a preference for the Y1-receptor.

Neuropeptide Y (NPY) is one of the most abundant neuropeptides in the mammalian brain and acts in humans via at least three receptor subtypes: Y1, Y2, and Y5. Whereas selective agonists and antagonists are known for the Y2- and Y5-receptors, the Y1-receptor still lacks a highly selective agonist. This work presents the first NPY-based analogues with Y1-receptor preference and agonistic properties. Furthermore, the importance of specific amino acids of NPY for binding to the Y-receptor subtypes is presented. Amongst the analogues tested, [Phe7,Pro34]pNPY (where pNPY is porcine neuropeptide Y) showed the most significant Y1-receptor preference (> 1 : 3000-fold), with subnanomolar affinity to the Y1-receptor, and Ki values of approximately 30 nM for the Y2- and Y5-subtype, respectively. Variations of position 6, especially [Arg6,Pro34]pNPY and variations within positions 20-23 of NPY were found to result in further analogues with significant Y1-receptor preference (1 : 400-1 : 2000). In contrast, cyclo S-S [Cys20,Cys24]pNPY was found to be a highly selective ligand at the Y2-receptor, binding only threefold less efficiently than NPY. Analogues containing variations of positions 31 and 32 showed highly reduced affinity to the Y1-receptor, while binding to the Y5-receptor was affected less. Inhibition of cAMP-accumulation of selected peptides with replacements within position 20-23 of NPY showed preserved agonistic properties. The NPY analogues tested give insights into ligand-receptor interaction of NPY at the Y1-, Y2- and Y5-receptor and contribute to our understanding of subtype selectivity. Furthermore, the Y1-receptor-preferring peptides are novel tools that will provide insight into the physiological role of the Y1-receptor.     

Inhibition of postpartum uterine involution in the rat by relaxin

The possible contribution of relaxin to the support of uterine accommodation during late gestation by retarding tissue lysis was examined using the involuting postpartum uteri of unilaterally pregnant rats. In otherwise intact animals, twice-daily administration of 0.1 mg of relaxin (porcine fraction B) significantly retarded the regression of both gravid and, to a greater extent, nongravid tissue during the first 4 days postpartum, and collagenolysis was similarly delayed. Immediate postpartum ovariectomy had little effect on the uterus, although 5 micrograms estradiol benzoate daily suppressed uterine involution in the gravid tissue to about 50% and was even more effective in the nongravid uterus. Relaxin alone had little effect on the gravid uterus following ovariectomy, but augmented estrogen to the extent that less than half of the tissue and its collagen were lost during 4 days. The effect on nongravid tissue was even more striking in that the combination of estrogen and relaxin prevented any degradation of tissue in general or of collagen. Although we have reported that relaxin can stimulate uterine collagen synthesis as well as uterine growth, the magnitude of its postpartum effect in the presence of estrogen suggests a stabilizing or anticatabolic effect upon the uterus.     

The synthesis of some branched-chain-sugar nucleoside analogues.

1-(2,3-Epoxy-5-O-trityl-beta-D-lyxofuranosyl)uracil was treated with a number of carbon nucleophiles. Ethynyl lithium gave 3'-deoxy-3'-ethynyl-5'-O-trityl-ara-uridine, which was reduced to the corresponding 3'-ethenyl compound. Sodium cyanide gave 3'-cyano-3'-deoxy-5'-O-trityl-ara-uridine which upon alkaline hydrolysis gave the corresponding 3'-carboxamido compound. 1,3-Dithian-2-yl lithium gave 3'-deoxy-3'-(1,3-dithian-2-yl)-5'-O-trityl-ara-uridine. The trityl group was removed from each of these compounds by mild acidic hydrolysis. Treatment of 2 with 0.1M H2sO4 and mercury (II) acetate afforded 3'-acetyl-3'-deoxy-ara-uridine which upon reduction with NaBH4 gave 3'-deoxy-3'-(1-hydroxyethan-1-yl)-ara-uridine. Acetylation of 6 yielded 5'-O-acetyl-3'-acetyl-2',3'-didehydro-2',3'-dideoxyuridine which upon reduction with NaBH4 produced a mixture of 5'-O-acetyl-2',3'-didehydro-2',3'-dideoxy-3'-(1-hydroxyethan -1-yl)uridine and 1-(R)[5-(S)-acetoxymethyl-4-(1-hydroxyethan-1-yl)-tetrahydrofuran- 2-yl]- uracil. Reduction of 14 with Raney nickel followed by removal of the trityl group gave 3'-deoxy-3'-methyl-ara-uridine.     

A new strategy for the synthesis of crucigasterin A,and cytotoxic activity of this compound and its related analogues

Stereoselective total synthesis of bioactive marine natural product crucigasterin A has been accomplished from commercially available and inexpensive l-(?)-malic acid as a starting material. Julia olefination and chelation controlled Grignard additions are the key steps involved in the present synthesis. Cytotoxic properties of crucigasterin A and its related analogues crucigasterins B and D have been evaluated. Crucigasterin A showed promising activities against both the human cervical cancer cell line and human breast adenocarcinoma cell line.