Search

The synthesis and biological activities of rapamycin (I) analogs modified at the C-40 position are reported. Emphasis placed on compounds that potentially have an improved safety profile on account of their shorter in vivo half-life when compared with rapamycin.

Interleukin-8 modulation is implicated in many inflammatory and cancer diseases. Starting from a mass-screening hit, the synthesis and structure-activity relationship of 2-amino-3-heteroarylquinoxalines as non-peptide, small molecule interleukine-8 receptor antagonists have been developed. The optimized derivatives, PD 0210293 (13y) and PD 0220245 (13r), show inhibition of both IL-8 receptor binding and IL-8-mediated neutrophil chemotaxis.

Several novel 4-substituted 4-arylpiperidines were synthesized. The chemistry leading to 4-(4-chlorophenyl)-4-fluoropiperidine ( 6 ), 4-azido-4-(4-chlorophenyl)piperidine ( 7 ) and 4-(4-chlorophenyl)-4-methylpiperidine ( 8 ) is described.

C24-Deoxyascomycin was prepared in a two-step process from ascomycin and evaluated for its immunosuppressant activity relative to ascomycin and FK506. An intermediate in the synthetic pathway, Delta(23,24)-dehydroascomycin, was likewise evaluated. Despite lacking the hydrogen-bonding interactions associated with the C24-hydroxyl moiety of ascomycin, C24-deoxyascomycin was found to be equipotent to the parent compound both in its immunosuppressive potency and in its interaction with the immunophilin, FKBP12. Conversely, Delta(23,24)-dehydroascomycin which also lacks the same hydrogen-bonding interactions did not exhibit this potency. NMR studies were conducted on the FKBP12/C24-deoxyascomycin complex in an attempt to understand this phenomenon at the molecular level. The NMR structures of the complexes formed between FKBP12 and ascomcyin or C24-deoxyascomcyin were very similar, suggesting that hydrogen-bonding interactions with the C24 hydroxyl moiety are not important for complex formation.

To assess the duration of immunosuppression in FK506-dosed pigs, an undiluted whole blood assay was established to measure reactivities of T cells in their physiological milieu. PMA and ionomycin were shown to induce IL-2 production in swine blood. The IC50of FK506 in inhibiting IL-2 production in whole blood and isolated PBMC stimulated with PMA and ionomycin measured 1.2 and 0.04 nM, respectively. These data underscore the influence of red blood cells and plasma proteins on drug potency. IL-2 levels were determined in blood drawn immediately before and 1, 24, 48, and 72 h after iv dosing. For pigs dosed with 0.05 mg/kg, 50% recovery of IL-2 production was observed at 16 h and 100% at 35 h after dosing. For pigs dosed with 0.15 mg/kg, 50% recovery was observed at 38 h and 100% at 72 h. Blood concentrations of FK506 at 50 and 100% recovery of IL-2 production measured 10.8 and 2.2 nM for pigs dosed with 0.05 mg/kg and 6.1 and 1.1 nM for pigs dosed with 0.15 mg/kg, respectively. These concentrations are severalfold higher than predicted from the IC50of FK506 for inhibiting IL-2 production in the whole blood assay. These data suggest that the true potency of FK506 in blood after dosing is influenced by additional factors, which could include plasma protein binding, the presence of active or interfering metabolites, serum interfering factors, and sequestration of drug in blood cells. Our results demonstrate the utility of an undiluted whole blood assay for assessing the duration of immunosuppression in drug-dosed animals and emphasize the importance of assessing drug potency in the whole blood environmentex vivo.

A series of novel pyrazole carboxamides is disclosed that demonstrate strong immunosuppressant activity in rodent and human mixed leukocyte response (MLR) assays (IC501 microM). The synthesis, biological activity, mode of action, and pharmacokinetic properties of this new lead series are discussed.

Ascomycin ( 1a ), a macrolactam antifungal antibiotic disclosed by Arai in 1962, 1 was found to display immunosuppressive activity more than 2 decades later by Okuhara and coworkers at Fujisawa. 2 Ascomycin ( 1a ) and FK506 ( 1b ) bind to a peptidyl-prolyl-isomerase, FKBP, a necessary but insufficient condition for drug activity. Both FK506 and ascomycin exist as a mixture of slowly interconverting cis and trans amide rotamers. It has also been shown that only the trans amide rotamer binds to FKBP. 24-epi-Ascomycin ( 3 ), 24-oxo-22-norascomyin ( 9a ), and 22-norascomycin ( 9b ), obtained by semisynthesis from ascomycin, exist as single rotamers on the NMR time scale. Their synthesis and the biological consequences of this observation are discussed.

Small acyclic model compounds were synthesized to examine the importance of the C(9) carbonyl group of KF506 for FKBP binding. 4-(4′-Methoxyphenyl)-1-butyl (3″, 4″, 5″-trimethoxyphenylglyoxyl) pipecolate (compound 2d), containing the N-(glyoxyl)pipecolate motif of FK506, was found to bind to FKBP with IC50 of 16 μM. Replacement of the carbonyl group at the position corresponding to C(9) of FK506 with small nonpolar groups (hydrogen, methylene or methyl group, compounds 2a–2c) significantly reduced the binding affinity.

The conformation of a water-soluble analog of the immunosuppressant FK506 was determined in aqueous solution using NMR spectroscopy. The three-dimensional structures for both the 7,8-cis and trans isomers of [32-Arg] ascomycin which are present in a 1:1 ratio were found to be quite different from FK506 in the crystal state or in chloroform solution but more closely resemble the structure of FK506 when bound to the FK506-binding protein (FKBP). These results suggest that the FKBP-bound conformation of FK506 largely preexists in aqueous solution and is not induced by the protein as previously postulated. In addition, using uniformly 15 N- 13 C-labeled FKBP and isotope-filtering NMR techniques, it is shown that FKBP binds exclusively the trans form of [32-Arg]ascomycin and does not catalyze the cis/trans interconversion of the inhibitor

The immunosuppressive agent FK-506 has received much attention due to its efficacy and potency in the areas of transplant rejection and autoimmune disease. Calcineurin, a Ca2+-calmodulin activated phosphatase, was recently implicated in the immunosuppressive mechanism of FK-506. In our ongoing search for superior immunosuppressive agents, we have synthesized several analogues of FK-506 and tested their mechanistic and immunosuppressive actions. It was found that C-18 hydroxyl analogues of ascomycin, an analogue of FK-506 also called FR900520, bound tightly to immunophilin FKBP-12, but do not show any immunosuppressive activity in vitro or in vivo despite good bioavail-ability. Further, they reverse the inhibition of calcineurin caused by FK-506/FKBP-12 complex.

Ascomycin (1) is a close analogue of the immunosuppressant FK-506 (2) which differs slightly in the side chain at position 21 (ethyl vs allyl). Structurally unique ascomycin and FK-506 are the subjects of intense chemical research because of their application in organ transplantation and autoimmune disease. We have been interested in studying the effect of structural modification and conformational change on biological activity. This paper reports the fermentation and structural determination of ascomycin as well as the synthesis and structure confirmation of a series of pyrazole analogues (3 and 4) derived from ascomycin.

Ascomycin (1) is a close analogue of the immunosuppressant FK-506 (2) which differs slightly in the side chain at position 21 (ethyl vs allyl). Structurally unique ascomycin and FK-506 are the subjects of intense chemical research because of their application in organ transplantation and autoimmune disease. We have been interested in studying the effect of structural modification and conformational change on biological activity. This paper reports the fermentation and structural determination of ascomycin as well as the synthesis and structure confirmation of a series of pyrazole analogues (3 and 4) derived from ascomycin.

Ascomycin 2, a close analogue of the immunosuppressant FK506 1, was modified to incorporate a hydroxyl group at the C-33 position. This increased the aqueous solubility of ascomycin by a hundred-fold at pH 7.4 and by approximately 300-fold at pH 6.5. Ascomycin 3 also exhibited an excellent immunosuppressive activity in vitro, as tested in a human mixed lymphocyte proliferation (HuMLR) assay, and in vivo using a rat popliteal lymph node (rPLN) hyperplasia assay.

A series of novel pyrazole carboxamides is disclosed that demonstrate strong immunosuppressant activity in rodent and human mixed leukocyte response (MLR) assays (IC50 < 1 μM). The synthesis, biological activity, mode of action, and pharmacokinetic properties of this new lead series are discussed.

The synthesis and structure-activity relationships of C-terminal octapeptide analogues of anaphylatoxin C5a have been studied. The introduction of hydrophobic amino acids into the N-acetylated native octapeptide (N-Ac-His-Lys-Asp-Met-Gln-Leu-Gly-Arg-OH) (1) has led to an analogue with 100 times more activity than the native octapeptide in inhibiting the binding of 125I-labeled anaphylatoxin C5a to human neutrophil membrane receptors. The observed apparent binding Ki's for the compounds (8-10) are in the range of 1-3 microM, and they possess nearly full agonist activity, despite the fact that these analogues are one-eighth or -ninth the size of the natural ligand anaphylatoxin C5a.

C5a is a 74 amino acid polypeptide that likely plays an important role in the pathogenesis of a number of inflammatory diseases. Therefore, the discovery of a C5a antagonist is of considerable therapeutic interest. A series of peptides designed to survey various regions of the molecule was synthesized by solid-phase peptide synthesis and evaluated for receptor-binding activity with polymorphonuclear leukocyte membranes. The C-terminal octapeptide (Ac-His-Lys-Asp-Met-Gln-Leu-Gly-Arg-OH) was identified as the smallest fragment which possessed reasonable C5a receptor binding activity.

An expedient method that allows modification of a cysteine residue side chain through alkylation of unprotected peptides is described. In order to test the generality of the method, an unprotected cysteine-containing tetrapeptide possessing several potentially competing nucleophilic functionalities such as amino, hydroxy, and carboxyl groups was chosen as a model peptide. The model tetrapeptide, H-Ser-Lys-Cys-Phe-OH was synthesized by standard solid-phase methods, cleaved with HF, and purified by reverse-phase HPLC. Reaction of the unprotected peptide with 1.3 equiv of various alkylating agents in saturated ammonia in methanol at 0 o C proceeded cleanly to yield single alkylation products within one hour as shown by HPLC analysis. In most cases acidic, basic, and neutral side chains were introduced by this method in over 80% yield. The methodology is also applicable to the synthesis of cyclic peptides by intramolecular cysteine alkylation and provides a useful alternative to cyclizations that occur through disulfide or amine bond-forming reactions as illustrated by the synthesis of a carbavasopressin

A novel series of barbituric acid derivatives were identified as selective inhibitors of alpha4beta7 MAdCAM (mucosal addressin cell adhesion molecule-1) interactions via a high throughput screening exercise. These inhibitors were optimized to submicromolar potencies in whole cell adhesion assays, retaining their selectivity over alpha4beta1 VCAM.

A novel class of functional ligands for the human glucocorticoid receptor is described. Substituents in the C-10 position of the tetracyclic core are essential for glucocorticoid receptor (GR) selectivity versus other steroid receptors. The C-5 position is derivatized with meta-substituted aromatic groups, resulting in analogues with a high affinity for GR (K(i) = 2.4-9.3 nM) and functional activity comparable to prednisolone in reporter gene assays of glucocorticoid-mediated gene transcription. The biological activity of these novel quinolines was also prednisolone-equivalent in whole cell assays of glucocorticoid function, and compound 13 was similar to prednisolone (po ED(50) = 2.8 mpk for 13 vs ED(50) = 1.2 mpk for prednisolone) in a rodent model of asthma (sephadex-induced eosinophil influx).

Several novel 4-substituted 4-arylpiperidines were synthesized. The chemistry leading to 4-(4-chlorophenyl)-4-fluoropiperidine ( 6 ), 4-azido-4-(4-chlorophenyl)piperidine ( 7 ) and 4-(4-chlorophenyl)-4-methylpiperidine ( 8 ) is described.

Ascomycin 2, a close analogue of the immunosuppressant FK506 1, was modified to incorporate a hydroxyl group at the C-33 position. This increased the aqueous solubility of ascomycin by a hundred-fold at pH 7.4 and by approximately 300-fold at pH 6.5. Ascomycin 3 also exhibited an excellent immunosuppressive activity in vitro, as tested in a human mixed lymphocyte proliferation (HuMLR) assay, and in vivo using a rat popliteal lymph node (rPLN) hyperplasia assay.

The structure determination by molecular replacement methods of a monoclinic pepsin/renin inhibitor complex crystal, with two molecules in the asymmetric unit, is presented. The atomic model, consisting of two liganded pepsin molecules and 110 water molecules, has been refined to a final crystallographic R value of 0.139 for data between 8 and 2.9 A resolution. The structure reveals a previously undescribed pepsin dimer formed predominantly by polar interactions. Inhibitor binding induces global structural changes in the native enzyme similar, but not identical, to the ones observed in other chemically similar pepsin/renin inhibitor complexes crystallized in an orthorhombic form. A region of the polypeptide chain (residues 292-297) which was not visible in the orthorhombic crystal is well ordered in the presently described structure; possibly induced by crystal contacts. The crystal packing of native pepsin is compared with the two different crystal forms of the inhibited enzyme.

Crystal structures of several fungal aspartic proteinases have been refined at high resolution: penicillopepsin1, Endothia parasitica pepsin2 and Rhizopus chinensis protease.3 The structure of a recombinant form of human renin has been solved4 at 2.5 A and the refined structures of two other mammalian aspartic proteinases have been reported recently: chymosin at 2.3 A resolution5, and the monoclinic form of porcine pepsin at 2.3 and 1.8 A resolution6,7, as well as the original hexagonal crystal form8.

The binding of a 13C-labeled cyclosporin A (CsA) analog to cyclophilin (peptidyl prolyl isomerase) was examined by means of isotope-edited nuclear magnetic resonance (NMR) techniques. A trans 9,10 peptide bond was adopted when CsA was bound to cyclophilin, in contrast to the cis 9,10 peptide bond found in the crystalline and solution conformations of CsA. Furthermore, nuclear Overhauser effects (NOEs) were observed between the zeta 3 and epsilon 3 protons of the methylleucine (MeLeu) residue at position 9 of CsA and tryptophan121 (Trp121) and phenylalanine (Phe) protons of cyclophilin, suggesting that the MeLeu9 residue of CsA interacts with cyclophilin. These results illustrate the power of isotope-edited NMR techniques for rapidly providing useful information about the conformations and active site environment of inhibitors bound to their target enzymes.

Stereoselective syntheses of several nonpeptide fragments that function as Leu10-Val11 scissile bond replacements in human angiotensinogen are presented. The opening of N-protected aminoalkyl epoxide 3 with a variety of sulfur, oxygen, nitrogen, and carbon nucleophiles is a key reaction in the preparation of these novel fragments 4-8. The coupling of these fragments to protected dipeptides that mimic positions 8 and 9 in angiotensinogen produces inhibitors of human renin even though the molecules contain no functionality beyond what is formally the Val11 side chain of angiotensinogen. R groups that closely resemble that of the Val side chain are preferable; thus, isopropyl greater than or equal to higher alkyl greater than phenyl greater than substituted phenyl. Sulfur is the best X group; oxidation leads to slight (X = SO2) and significant (X = SO) decreases in inhibitory potency. One such inhibitor, 60, has an IC50 of 13 nM when tested with purified human renin at pH 6.0. The significant activity of these small inhibitors is thought to be due in part to the hydroxyl group of the fragment functioning as a transition-state analogue. Of these, the inhibitors that contain histidine show marked selectivity toward renin over a related aspartic proteinase, pepsin.

Synthese d'α-aminoaldehydes (A) par reduction des aminoesters ou par oxydation des aminoalcools correspondants; par reaction de Wittig sur ces composes A, on obtient des α-alkyl allylamines N-protegees qui sont ensuite epoxydees

Stereoselective syntheses of several nonpeptide sulfidoethanol fragments that function as Leu10-Val11 (P1-P1') scissile bond replacements in human angiotensinogen are presented. These fragments are prepared from a variety of amino acids with formal P1 side chains varying in size and lipophilicity by converting them to their corresponding N-protected aminoalkyl epoxide 5 followed by ring opening with isopropyl mercaptan. The coupling of these fragments to either Boc-Phe-Ala-OH or Boc-Phe-His-OH produces inhibitors of human renin, 6 and 7, respectively, which are compared to a series of dipeptide-aldehyde inhibitors, 4, by molecular modeling and biochemical methods. Qualitatively, histidine-containing (P2) inhibitors 7 possess greater inhibitory potency than their corresponding alanine (P2) analogues 6, which are more potent than the corresponding aldehydic inhibitors from series 4. Within a given series, inhibitors with the cyclohexylmethyl P1 side chain are more potent than the benzyl analogues, which in turn are more potent than cyclohexyl or isobutyl derivatives. Inhibitors with parger P1 side chains (e.g. adamantylmethyl and benzhydryl) are much less active. The inhibitory potency of these compounds against human renin is discussed in terms of specific interactions with the enzyme.

From a series of isotope-edited proton NMR spectra, amide proton exchange rates were measured at 20 degrees C, 30 degrees C, and 40 degrees C for a tightly bound 15N-labeled tripeptide inhibitor of porcine pepsin (IC50 = 1.7 X 10(-) M). Markedly different NH exchange rates were observed for the three amide protons of the bound inhibitor. The P1 NH exchanged much more slowly than the P2 NH and P3 NH. These results are discussed in terms of the relative solvent accessibility in the active site and the role of the NH protons of the inhibitor for hydrogen bonding to the enzyme. In this study a useful approach is demonstrated for obtaining NH exchange rates on ligands bound to biomacromolecules, the knowledge of which could be of potential utility in the design of therapeutically useful nonpeptide enzyme inhibitors from peptide leads.

A new class of angiotensinogen analogues which contain heteroatom-methylene and retro-inverso amide bond replacements was synthesized and evaluated for renin inhibition. Selected compounds in the series were specific for renin over other aspartic proteinases, and the most potent inhibitor demonstrated hypotensive activity in a salt depleted monkey.

We have designed a novel class of potent (0.3-7 nM) renin inhibitors which contain a dihydroxyethylene replacement for what is formally the Leu10-Val11 amide bond. Good potency (0.6 nM), water solubility (greater than 10 mg/ml at 37 degrees C), stability toward degradation by chymotrypsin (t1/2 = 820 min), and in vivo activity in a primate model (15% drop in mean arterial pressure in association with complete inhibition of plasma renin activity) are properties which have been incorporated into compound 10, an interesting new agent to be used in the study of hypertension.

The 3D structure of two unlabeled FK506 analogs, (R)- and (S)-[18-OH]ascomycin, when bound to [U-13C,14N]FKBP were determined by isotope-filtered 2D NMR experiments. The structures for the R and S isomers that bind tightly to FKBP but lack immunosuppresive activity are compared to each other and to the conformation of the potent immunosuppressant, ascomycin, when bound to FKBP. The results are interpreted in terms of calcineurin binding to the FKBP/ascomycin complex.

A general approach is illustrated for providing detailed structural information on large enzyme/inhibitor complexes using NMR spectroscopy. The method involves the use of isotopically labeled ligands to simplify two-dimensional NOE spectra of large molecular complexes by isotope-editing techniques. With this approach, the backbone and side-chain conformations (at the P/sub 2/ and P/sub 3/ sites) of a tightly bound inhibitor of porcine pepsin have bene determined. In addition, structural information on the active site of pepsin has been obtained. Due to the sequence homology between porcine pepsin and human renin, this structural information may prove useful for modeling renin/inhibitor complexes with the ultimate goal of designing more effective renin inhibitors. Moreover, this general approach can be applied to study other biological systems of interest such as other enzyme/inhibitor complexes, ligands bound to soluble receptors, and enzyme/substrate interactions.