Enantioselective strategy to the spirocyclic core of Palau'amine and related bisguanidine marine alkaloids

[structure: see text] An enantioselective strategy to the spirocyclic core found in the oroidin-derived family of bisguanidine marine alkaloids has been devised, premised on a biosynthetic proposal. Herein, we describe the successful implementation of this strategy, which entails a Diels-Alder reaction and a chlorination/ring contraction sequence that delivers the fully functionalized spirocyclic core. In this initial report, an intermolecular chlorination delivers a cyclopentane that is epimeric at C17 relative to the palau'amines and epimeric at C11 relative to the axinellamines.

A murine IL-4 receptor antagonist that inhibits IL-4- and IL-13-induced responses prevents antigen-induced airway eosinophilia and airway hyperresponsiveness

The closely related Th2 cytokines, IL-4 and IL-13, share many biological functions that are considered important in the development of allergic airway inflammation and airway hyperresponsiveness (AHR). The overlap of their functions results from the IL-4R alpha-chain forming an important functional signaling component of both the IL-4 and IL-13 receptors. Mutations in the C terminus region of the IL-4 protein produce IL-4 mutants that bind to the IL-4R alpha-chain with high affinity, but do not induce cellular responses. A murine IL-4 mutant (C118 deletion) protein (IL-4R antagonist) inhibited IL-4- and IL-13-induced STAT6 phosphorylation as well as IL-4- and IL-13-induced IgE production in vitro. Administration of murine IL-4R antagonist during allergen (OVA) challenge inhibited the development of allergic airway eosinophilia and AHR in mice previously sensitized with OVA. The inhibitory effect on airway eosinophilia and AHR was associated with reduced levels of IL-4, IL-5, and IL-13 in the bronchoalveolar lavage fluid as well as reduced serum levels of OVA-IGE: These observations demonstrate the therapeutic potential of IL-4 mutant protein receptor antagonists that inhibit both IL-4 and IL-13 in the treatment of allergic asthma.

Small molecule inhibitors of serine/threonine protein phosphatases

Serine/threonine protein phosphatases have long been ignored as potential therapeutic targets for two reasons, one the biochemical significance of these proteins has not been appreciated and two, many natural protein phosphatase inhibitors are potent toxins and are considered unsuitable for clinical use. This review outlines the biochemical role of this protein family in cancer, cystic fibrosis, immunosuppression and, cardiac and neurological disorders. Particular emphasis is also given to the synthesis of selective small molecule inhibitors and their clinical exploitation.

Total synthesis of a conformationally constrained didemnin B analog

The total synthesis of a didemnin B analogue containing a conformationally constrained replacement for the isostatine moiety is reported. Synthetic highlights include an improved preparation of 2-hydroxy-3-cyclohexenecarboxylic acid and a new strategy for accessing the macrocycle.

Angular methoxy-substituted furo- and pyranoquinolinones as blockers of the voltage-gated potassium channel Kv1.3

The voltage-gated potassium channel Kv1.3 constitutes an attractive target for immunosuppression because of its role in T-lymphocyte activation and its functionally restricted expression to lymphocytes. Blockade of Kv1.3 channels by margatoxin has previously been shown to prevent T-cell activation and attenuate immune responses in vivo. In the present study, several furo- and pyranoquinoline derivatives were synthesized and screened for their blocking activities of Kv1.3 channels, stably expressed in mice-fibroblasts L929. In addition the activities of the compounds on Kv currents of the neuroblastoma cell line N1E-115 were determined. The most potent compounds, the angular furoquinolinone 8-methoxy-2-(1'-methylethyl)-5-methyl-4,5-dihydrofuro[3,2-c]quinolin-4-one (8c) and the angular pyranoquinolinone 9-methoxy-2,2,6-trimethyl-2,6-dihydro-5H-pyrano[3,2-c]quinolin-5-one (9a), inhibited Kv1.3 channels with half-blocking concentrations of 5 and 10 microM, respectively, and displayed 8-fold (8c) and 2-fold (9a) selectivity over Kv currents of N1E-115 cells. Thus, compounds 8c and 9a might function as a template for the development of novel immunosuppressants.

Structure-based design of a bispecific receptor mimic that inhibits T cell responses to a superantigen

Key surface proteins of pathogens and their toxins bind to the host cell receptors in a manner that is quite different from the way the natural ligands bind to the same receptors and direct normal cellular responses. Here we describe a novel strategy for "non-antibody-based" pathogen countermeasure by targeting the very same "alternative mode of host receptor binding" that the pathogen proteins exploit to cause infection and disease. We have chosen the Staphylococcus enterotoxin B (SEB) superantigen as a model pathogen protein to illustrate the principle and application of our strategy. SEB bypasses the normal route of antigen processing by binding as an intact protein to the complex formed by the MHC class II receptor on the antigen-presenting cell and the T cell receptor. This alternative mode of binding causes massive IL-2 release and T cell proliferation. A normally processed antigen requires all the domains of the receptor complex for its binding, whereas SEB requires only the alpha1 subunit (DRalpha) of the MHC class II receptor and the variable beta subunit (TCRVbeta) of the T cell receptor. This prompted us to design a bispecific chimera, DRalpha-linker-TCRVbeta, that acts as a receptor mimic and prevents the interaction of SEB with its host cell receptors. We have adopted (GSTAPPA)(2) as the linker sequence because it supports synergistic binding of DRalpha and TCRVbeta to SEB and thereby makes DRalpha-(GSTAPPA)(2)-TCRVbeta as effective an SEB binder as the native MHC class II-T cell receptor complex. Finally, we show that DRalpha-(GSTAPPA)(2)-TCRVbeta inhibits SEB-induced IL-2 release and T cell proliferation at nanomolar concentrations.

Rational design of biologically active peptides: inhibition of T cell activation through interference with CD4 function. Transplant Int (2000) 13 [Suppl 1]: S306-S310

In our laboratory we generated one synthetic cyclic peptide (Pep4) and tested it in human mitogen stimulation assays (MSA) and mixed lymphocytes reactions (MLR) generating dose-response curves showing a dose-dependent inhibition of MSA up to 80% and MLR up to 98%. MSA and MLR were repeated after pre incubation of the Pep4 with each separate responder cell subset and subsequent reconstitution: these experiments showed inhibition only when the peptide was present in culture. Pep4 showed species specificity since it was ineffective in inhibiting rat MLR. Combination effect analysis with Pep4 and cyclosporine showed a combination index > 1. This rationally designed peptide (Pep4) shows powerful inhibition of human T cell activation and, although the exact mechanism is still undefined, it seems to exert its major action on the T cell surface, interfering with co receptor interaction and disrupting the same activation signal pathway inhibited by cyclosporine A.

Total synthesis of FR901483

[structure: see text]. The total synthesis of FR901483, a structurally novel immunosuppressant, has been accomplished by the use of technology recently developed in this laboratory for the oxidative cyclization of phenolic oxazolines to spirolactams. Our approach may reflect the biosynthetic pathway leading to the natural product.

Total synthesis of the immunosupressant (-)-pironetin (PA48153C)

[reaction: see text]. Total synthesis of the immunosuppresant pironetin has been achieved by a synthetic route in which the connections between starting materials and the desired structure are readily discerned. Key steps include a diastereoselective Lewis acid mediated crotylstannane aldehyde addition, a highly selective Lewis acid promoted Mukaiyama aldol reaction, an anti-selective SmI2 reduction of a beta-hydroxyketone, and finally a lactone annulation reaction.

Reactions of 5-amino-3-methylisoxazole-4-carboxylic acid hydrazide with carbonyl compounds: immunological activity and QSAR studies of products

A series of 4-imino derivatives of the 5-amino-3-methylisoxazole-4-carboxylic acid hydrazide and 5-amino-3-methylisoxazole[5,4-d]-6,7-dihydropyrimidine has been prepared by condensation of 5-amino-3-methylisoxazole-4-carboxylic acid hydrazide with carbonyl compounds. The resulting products were evaluated for their immunological activities in the models of the humoral and cellular immune responses of mice in vivo and concanavalin A (Con A) and lipopolysaccharide (LPS)-induced splenocyte proliferation. In addition, effects on polyclonal antibody production by human peripheral blood cells in culture were investigated. For all studied compounds we carried out quantum chemical calculations at ab initio B3LYP 6-31G(d, p) level. The stimulatory or inhibitory effects depended strongly on the origin and location of substitunets, which is described in the conclusions and was supported by QSAR studies.

Multimodular biocatalysts for natural product assembly

Nonribosomal peptides and polyketides represent a large class of natural products that show an extreme structural diversity and broad pharmacological relevance. They are synthesized from simple building blocks such as amino or carboxy acids and malonate derivatives on multimodular enzymes called nonribosomal peptide synthetases (NRPSs) and polyketide synthases (PKSs), respectively. Although utilizing different substrates, NRPSs and PKSs show striking similarities in the modular architecture of their catalytic domains and product assembly-line mechanism. Among these compounds are well known antibiotics (penicillin, vancomycin and erythromycin) as well as potent immunosuppressive agents (cyclosporin, rapamycin and FK 506). This review focuses on the modular organization of NRPSs, PKSs and mixed NRPS/PKS systems and how modules and domains that build up the biosynthetic templates can be exploited for the rational design of recombinant enzymes capable of synthesizing novel compounds.

Manipulation of polyketide biosynthesis for new drug discovery

Modular polyketide synthases (PKS) are large multifunctional proteins which direct the condensation of activated short chain carboxylic acids into products of defined length and functionality using a dedicated set of active sites, or module, for each step in the polymerization. The structure of the product is directly related to the number, content and sequence of modules in a PKS. Technology is described which allows the rational manipulation of the biosynthesis of these compounds and enables the generation of specific novel polyketide structures. Examples of polyketide drugs whose structures may be manipulated using this technology are given.

Candelalides A-C: novel diterpenoid pyrones from fermentations of Sesquicillium candelabrum as blockers of the voltage-gated potassium channel Kv1.3

[figure: see text] Blockers of the voltage-gated potassium channel Kv1.3 are potential immunosuppressants. Candelalides A-C are three novel diterpenoid pyrones that block this channel. The structure, stereochemistry, and activity against Kv1.3 are described.

Pseudoprolines (psiPro) in drug design: direct insertion of psiPro systems into cyclosporin C

The insertion of acetals that exhibit variable structural features into complex peptides such as cyclosporin C (CsC) results in oxazolidine derivatives (pseudoprolines, psiPro) of tailored physico-chemical and biological properties. N,O-Acetalation of the 2-threonine hydroxyl group and the preceding amide nitrogen of CsC is achieved by treating the molecule with a number of both arylated and non-arylated dimethyl acetals. The psiPro-containing CsC derivatives exhibit enhanced conformational backbone rigidity, as suggested by analytical HPLC, NMR spectroscopy and by kinetic measurements on binding with their receptor protein cyclophilin A (CypA) that were not time-dependent. IC50 values for calf-thymus CypA were obtained by kinetic evaluation of its cis-->trans isomerase activity. The choice of the para-substituted aryl dimethyl acetals allows the inhibitory properties of the corresponding derivatives to be modulated to either prodrugs or moderately strongly binding cyclosporin C derivatives.

The synthesis of (+)-preussin and related pyrrolidinols by diastereoselective Paternò-Büchi reactions of chiral 2-substituted 2,3-dihydropyrroles

The N-alkoxycarbonyl substituted 2,3-dihydropyrroles 3 and 8 are converted to 2-benzyl-3-pyrrolidinols by the Paternò - Büchi reaction followed by hydrogenolysis. Since the addition of the photoexcited benzaldehyde at the unsaturated heterocycle proceeds in a syn fashion, the benzyl group at C-2 and the hydroxy group at C-3 of the product are cis oriented. The simple and facial diastereoselectivities of the Paternò-Büchi reaction were studied more closely and the relative configuration of the products was elucidated. The thermodynamically less stable endo product is formed as a result of simple diastereoselection. The face differentiation in 2-substituted 2,3-dihydropyrroles is presumably due to the nonplanarity of these heterocycles, which forces attack of the carbonyl group on the face with the existing substituent. All-cis-pyrrolidinols are consequently formed after hydrogenolysis. Following this route, a total synthesis of the pyrrolidinol alkaloid (+)-preussin (1) was conducted, which yielded the target compound in a total yield of 11% over nine steps starting from L-pyroglutaminol (11).

Recent advances in the design and synthesis of SH2 inhibitors of Src, Grb2 and ZAP-70

A perspective is offered on the recent development of Src-homology 2 (SH2) antagonists of Src, Grb2 and ZAP-70. Inhibiting Src SH2 is believed to be a potentially attractive way of regulating bone resorption. Grb2 SH2 has been shown to be an important component of the mitogenic ras pathway; and thus might be of utility in cancer research. ZAP-70 is a tyrosine kinase that is expressed solely in T-cells and natural killer cells. Since inhibition of the tandem SH2 domains of ZAP-70 has been shown to block T-cell proliferation, antagonists for this particular protein could have implications in immune suppression. The emphasis of the article is placed on the structure-based design, synthesis and biological activity of a number of newly reported SH2 antagonists in each of the three areas.

Conceptually new 20-epi-22-oxa sulfone analogues of the hormone 1alpha,25-dihydroxyvitamin D(3): synthesis and biological evaluation

New C,D-ring side-chain-modified sulfone 4a, with natural 1alpha, 3beta-hydroxyl groups but lacking the 25-hydroxyl group characteristic of the natural hormone 1alpha,25-dihydroxyvitamin D(3) (1), has been prepared and characterized. Novel synthetic features include: (1) chemoselective oxidation of only a primary silyl ether in a primary-secondary bis-silyl ether intermediate and (2) smooth reductive etherification without interference by a neighboring sulfonyl group. Sulfone 4a, but not its 1beta, 3alpha-diastereomer 4b, is powerfully antiproliferative and transcriptionally active in vitro but desirably noncalcemic in vivo. Although sulfone 4a, designed to resemble Leo Pharmaceutical Co.'s KH-1060 (3), is recognized by catabolic enzymes, the selective biological profile of sulfone 4a is likely not due to its metabolites that are formed in only minor amounts.

Self-regeneration of stereocenters: a practical enantiospecific synthesis of LFA-1 antagonist BIRT-377

[reaction: see text] An efficient enantiospecific synthesis of the LFA-1 antagonist BIRT-377 has been achieved in 43% overall yield in eight steps. The key transformations involve the stereospecific formation of the trans imidazolidinone 7, subsequent alkylation, and the efficient hydrolysis of disubstituted imidazolidinone 9. The process is practical, robust, and cost-effective; it has been successfully implemented in the pilot plant to produce multikilogram quantities of the drug BIRT-377.

3,5-Bis(trifluoromethyl)pyrazoles: a novel class of NFAT transcription factor regulator

A series of bis(trifluoromethyl)pyrazoles (BTPs) has been found to be a novel inhibitor of cytokine production. Identified initially as inhibitors of IL-2 synthesis, the BTPs have been optimized in this regard and even inhibit IL-2 production with a 10-fold enhancement over cyclosporine in an ex vivo assay. Additionally, the BTPs show inhibition of IL-4, IL-5, IL-8, and eotaxin production. Unlike the IL-2 inhibitors, cyclosporine and FK506, the BTPs do not directly inhibit the dephosphorylation of NFAT by calcineurin.

Synthesis and immunosuppressive activity of 2-substituted 2-aminopropane-1,3-diols and 2-aminoethanols

A series of 2-substituted 2-aminopropane-1,3-diols was synthesized and evaluated for their lymphocyte-decreasing effect and immunosuppressive effect on rat skin allograft. A phenyl ring was introduced into the alkyl chain of the lead compound 3, which is an immunosuppressive agent structurally simplified from myriocin (1, ISP-I) via compound 2. The potency of the various compounds was dependent upon the position of the phenyl ring within the alkyl side chain. The most suitable length between the quaternary carbon atom and the phenyl ring was two carbon atoms. 2-Substituted 2-aminoethanols were successively synthesized and evaluated for their T-cell-decreasing effect and immunosuppressive effect using a popliteal lymph node gain assay in rats. The absolute configuration at the quaternary carbon affected the activity, and the (pro-S)-hydroxymethyl group of compound 6 was essential for potent immunosuppressive activity. Favorable substituents for the (pro-R)-hydroxymethyl group of 6 were hydroxyalkyl (hydroxyethyl and hydroxypropyl) or lower alkyl (methyl and ethyl) groups. 2-Amino-2-[2-(4-octylphenyl)ethyl]propane-1,3-diol hydrochloride (6, FTY720) was found to possess considerable activity and is expected to be useful as an immunosuppressive drug for organ transplantation.

Discovery of novel and potent retinoic acid receptor alpha agonists: syntheses and evaluation of benzofuranyl-pyrrole and benzothiophenyl-pyrrole derivatives

In the course of our studies on retinoic acid receptor (RAR) agonists, we have designed and synthesized a series of benzofuran and benzothiophene derivatives. Some of these compounds (1a,b,e,f,j) markedly inhibited LPS-induced B-lymphocyte proliferation and exerted RARalpha selectivity. One of them, 4-[5-(4,7-dimethylbenzofuran-2-yl)pyrrol-2-yl]benzoic acid (1b), when orally administered significantly inhibited mouse antibody production and delayed type hypersensitivity (DTH) responses from a dose of 0.1 mg/kg.

Synthesis and immunosuppressive activity of novel prodigiosin derivatives

Prodigiosins (Ps) represent a family of naturally occurring red pigments characterized by a common pyrrolylpyrromethene skeleton. Some members of this family have been shown to possess interesting immunosuppressive properties exerted with a novel mechanism of action, different from that of currently used drugs. In fact, Ps inhibit phosphorylation and activation of JAK-3, a cytoplasmic tyrosine kinase associated with a cell surface receptor component called common gamma-chain, which is exclusive of all IL-2 cytokine family receptors. Blocking common gamma-chain transduction activity results in a potent and specific immunosuppressive activity. With respect to the interesting and unexploited immunomodulating properties of this family of compounds we initiated a medicinal chemistry program aimed at finding novel prodigiosin derivatives with improved immunosuppressive activity and lower toxicity. Utilizing an unprecedented and flexible way of assembling the prodigiosin frame, a number of new derivatives have been prepared and tested leading to the choice of 4-benzyloxy-5-[(5-undecyl-2H-pyrrol-2-ylidene)methyl]-2, 2'-bi-1H-pyrrole (PNU-156804, 16) as a lead immunosuppressant.

The immunosuppressory and adhesive miniregion of the human major histocompatibility protein, human leukocyte antigen DQ

Our previous studies showed that the nonapeptide fragment of human leukocyte antigen DQ with the TPQRGDVYT sequence strongly suppresses the immune response [Z. Szewczuk, I. Z. Siemion, and Z. Wieczorek (1996) Molecular Immunology, 33, 903-9081]. The fragment contains the RGDVY sequence, which is very similar to thymopentin (pentapeptide RKDVY, an active fragment (32-36) of thymopoietin, an immune system activator produced in thymi), and at the same time contains the RGD sequence, known as an inhibitor of adhesion processes. In the present study we tested an influence of the nonapeptide and its shorter fragments on binding the activated platelets and K562 cells to fibrinogen and fibronectin, respectively. We also designed and synthesized a cyclic thymopentin-like peptide. C*RGDVYC* (where C* indicates Cys participating in disulfide bridge) to restrict its conformation. The cyclization product strongly suppresses the humoral and cellular immune response and selectively inhibits the adhesion of K562 cells to fibronectin. The results are discussed in the light of CD conformational studies.