Solid-phase carbohydrate synthesis via on-bead protecting group chemistry

Di- and tri-saccharides were synthesized on a solid phase. The procedure started with a non-protected sugar linked via either cysteine or glutamine to a polystyrene resin. Selective dimethoxytritylation chemistry and subsequent steps yielded a resin-bound acceptor that could be glycosylated to yield β1,6-linked disaccharides. Reiteration of the procedure produced the trisaccharide.     

Suppression of inducible nitric oxide synthase expression by yakuchinones and their analogues

Analogues of yakuchinones were synthesized as inhibitors of nitric oxide production in lipopolysaccharide-activated macrophage cell line, RAW 264.7 cells. We prepared stronger inhibitors than the original natural molecules, yakuchinones A and B reported from Alpinia oxyphylla. From the limited structural activity relation study of analogues, we concluded that the optimal length of linker between two aryl groups and the presence of enone moiety in the linker were identified as essential for the activity. The IC50 value of the most potent structure was 0.92 microM. The active analogues suppressed the expression of inducible nitric oxide synthase protein and mRNA.     

Structure-based discovery and in-parallel optimization of novel competitive inhibitors of thymidylate synthase.

BACKGROUND: The substrate sites of enzymes are attractive targets for structure-based inhibitor design. Two difficulties hinder efforts to discover and elaborate new (nonsubstrate-like) inhibitors for these sites. First, novel inhibitors often bind at nonsubstrate sites. Second, a novel scaffold introduces chemistry that is frequently unfamiliar, making synthetic elaboration challenging. RESULTS: In an effort to discover and elaborate a novel scaffold for a substrate site, we combined structure-based screening with in-parallel synthetic elaboration. These techniques were used to find new inhibitors that bound to the folate site of Lactobacillus casei thymidylate synthase (LcTS), an enzyme that is a potential target for proliferative diseases, and is highly studied. The available chemicals directory was screened, using a molecular-docking computer program, for molecules that complemented the three-dimensional structure of this site. Five high-ranking compounds were selected for testing. Activity and docking studies led to a derivative of one of these, dansyltyrosine (Ki 65 microM). Using solid-phase in-parallel techniques 33 derivatives of this lead were synthesized and tested. These analogs are dissimilar to the substrate but bind competitively with it. The most active analog had a Ki of 1.3 microM. The tighter binding inhibitors were also the most specific for LcTS versus related enzymes. CONCLUSIONS: TS can recognize inhibitors that are dissimilar to, but that bind competitively with, the folate substrate. Combining structure-based discovery with in-parallel synthetic techniques allowed the rapid elaboration of this series of compounds. More automated versions of this approach can be envisaged.     

Synthesis and enzyme inhibitory activity of the s-nucleoside analogue of the ribitylaminopyrimidine substrate of lumazine synthase and product of riboflavin synthase

Lumazine synthase and riboflavin synthase catalyze the last two steps in the biosynthesis of riboflavin. To obtain structural and mechanistic probes of these two enzymes, as well as inhibitors of potential value as antibiotics, a sulfur analogue of the pyrimidine substrate of the lumazine synthase-catalyzed reaction and product of the riboflavin synthase-catalyzed reaction was designed. Facile syntheses of the S-nucleoside 5-amino-6-(D-ribitylthio)pyrimidine-2,4(1H,3H)-dione hydrochloride (15) and its nitro precursor 5-nitro-6-(D-ribitylthio)pyrimidine-2,4(1H,3H)-dione (14) are described. These compounds were tested against lumazine synthase and riboflavin synthase obtained from a variety of microorganisms. Compounds 14 and 15 were found to be inhibitors of both riboflavin synthase and lumazine synthase. Compound 14 is an inhibitor of Bacillus subtilis lumazine synthase (Ki 26 microM), Schizosaccharomyces pombe lumazine synthase (Ki 2.0 microM), Mycobacterium tuberculosis lumazine synthase (Ki 11 microM), Escherichia coli riboflavin synthase (Ki 2.7 microM), and Mycobacterium tuberculosis riboflavin synthase (Ki 0.56 muM), while compound 15 is an inhibitor of B. subtilis lumazine synthase (Ki 2.6 microM), S. pombe lumazine synthase (Ki 0.16 microM), M. tuberculosis lumazine synthase (Ki 31 microM), E. coli riboflavin synthase (Ki 47 microM), and M. tuberculosis riboflavin synthase (Ki 2.5 microM).     

Systematic syntheses and inhibitory activities of bisubstrate-type inhibitors of sialyltransferases

Bisubstrate-type sialyltransferase inhibitors 1/2a-e, having CMP-NeuAc and N-acetyllactosamine (or lactose) moieties connected by an alkanedithiol linker, were synthesized systematically. A uniform synthetic strategy was adopted that consists of consecutive couplings of three components (N-acetyllactosamine or lactose, sialic acid, and CMP), followed by oxidation. Due to the sensitivity of the compounds under alkaline conditions, final deprotection required careful monitoring by (1)H NMR. The inhibitory activities of 1/2a-e toward ST6N and ST3N indicated that both the structure of the acceptor moiety and the distance between donor and acceptor moieties were important.     

New synthetic routes to chain-extended selenium, sulfur, and nitrogen analogues of the naturally occurring glucosidase inhibitor salacinol and their inhibitory activities against recombinant human maltase glucoamylase

Six heteroanalogues (X = S, Se, NH) of the naturally occurring glucosidase inhibitor salacinol, containing polyhydroxylated, acyclic chains of 6-carbons, were synthesized for structure-activity studies with different glycosidase enzymes. The target zwitterionic compounds were synthesized by means of nucleophilic attack of the PMB-protected 1,4-anhydro-4-seleno-, 1,4-anhydro-4-thio-, and 1,4-anhydro-4-imino-D-arabinitols at the least hindered carbon atom of 1,3-cyclic sulfates. These 1,3-cyclic sulfates were derived from D-glucose and D-galactose, and significantly, they utilized butane diacetal as the protecting groups for the trans 2,3-diequatorial positions. Deprotection of the coupled products proceeded smoothly, unlike in previous attempts with different protecting groups, and afforded the target selenonium, sulfonium, and ammonium sulfates with different stereochemistry at the stereogenic centers. The four new heterosubstituted compounds (X = Se, NH) inhibited recombinant human maltase glucoamylase (MGA), one of the key intestinal enzymes involved in the breakdown of glucose oligosaccharides in the small intestine. The two selenium derivatives each had Ki values of 0.10 microM, giving the most active compounds to date in this general series of zwitterionic glycosidase inhibitors. The two nitrogen compounds also inhibited MGA but were less active, with Ki values of 0.8 and 35 microM. The compounds in which X = S showed Ki values of 0.25 and 0.17 microM. Comparison of these data with those reported previously for related compounds reinforces the requirements for an effective inhibitor of MGA. With respect to chain extension, the configurations at C-2' and C-4' are critical for activity, the configuration at C-3', bearing the sulfate moiety, being unimportant. It would also appear that the configuration at C-5' is important but the relationship is dependent on the heteroatom.     

Synthesis of multivalent Streptococcus suis adhesion inhibitors by enzymatic cleavage of polygalacturonic acid and 'click' conjugation

A galabiose disaccharide building block was synthesized by an efficient pectinase cleavage of polygalacturonic acid and subsequent chemical functional group transformations. Besides the disaccharide, the corresponding trisaccharide was also obtained and modified. The compounds were subsequently conjugated to dendrimers with up to eight end groups using 'click' chemistry. The compounds were evaluated as inhibitors of adhesion of the pathogen Streptococcus suis in a hemagglutination assay and strong inhibition was observed for the tetra- and octavalent galabiose compound with MIC values in the low nanomolar range. The corresponding octavalent trisaccharide was a ca. 20-fold weaker inhibitor.     

Stereoselective Synthesis of the Hexasaccharide Repeating Unit of the Cell Wall Polysaccharide from Kineosporia aurantiaca VKM Ac-720T Employing the Direct Glycosylation with Anomeric Hydroxy Sugars Involving Glycosyl Phthalate Intermediates

Synthesis of a suitably protected form of the hexasaccharide repeating unit of the cell wall polymer from Kineosporia aurantiaca VKM Ac-720 ^T has been achieved by the stereoselective direct glycosylation of a trisaccharide acceptor with a trisaccharide donor having an anomeric hydroxy group involving a glycosyl phthalate intermediate. Both the trisaccharide acceptor and the trisaccharide donor were obtained from a common trisaccharide, of which two β-mannopyranosyl linkages were constructed stereoselectively by employing the direct glycosylation method with the anomeric hydroxy sugar involving a glycosyl phthalate intermediate and the 2′-carboxybenzyl glycoside method, respectively.     

Synthesis of biantennary complex-type nonasaccharyl asn building blocks for solid-phase glycopeptide synthesis

The biantennary complex-type N-glycans bearing LacNAc and LacdiNAc as the nonreducing end motif were synthesized in a protected form suitable to use in the Fmoc solid-phase peptide synthesis studies. Two approaches for the nonasaccharide synthesis were examined by taking advantage of the highly β-selective glycosylation with GlcNTCA (N-phenyl)trifluoroacetimidate. An earlier approach, which involved the reaction of the trisaccharide donor (Gal-GlcNTCA-Man) and trisaccharide acceptor (Man-GlcNPhth(2)-N(3)), produced a mixture of nonasaccharide isomers. On the other hand, mannosylation of the trisaccharide acceptor (Man-GlcNPhth(2)-N(3)) stereoselectively afforded the known pentasaccharide (Man(3)-GlcNPhth(2)-N(3)), which was reacted with the disaccharyl glycosyl donor (Gal-GlcNTCA or GalNTCA-GlcNTCA) to produce the desired nonasaccharide as a single stereoisomer. Selective dephthaloylation followed by N-acetylation furnished the GlcNAc(2) functionality. The resulting nonasaccharyl azides were condensed with Fmoc-Asp(OPfp)-OBu(t) or Fmoc-Asp(OPfp)-OPac in the presence of Ph(CH(3))(2)P and HOOBt. Finally, the Zn reduction and cleavage of the tert-butyl ester or Zn reduction alone produced the targeted nonasaccharyl Asn building blocks.     

A novel linker for solid-phase synthesis cleavable under neutral conditions

A novel linker cleavable under neutral conditions has been developed for the solid-phase synthesis of base-labile compounds. The linker is comprised of a 3-azidomethyl-4-hydroxybenzyl alcohol moiety, and the azidomethyl group in the linker is readily converted to an aminomethyl group by treatment with a phosphine reagent in the presence of water to result in an intramolecular cyclization to release the compounds. Using the linker, a base-labile dinucleoside methyl phosphate was synthesized on a highly cross-linked polystyrene (HCP) support and cleaved successfully from the resin without decomposition of the product.     

Cleavable hydrophilic linker for one-bead-one-compound sequencing of oligomer libraries by tandem mass spectrometry

We have developed a method for the rapid and unambiguous identification of sequences of hit compounds from one-bead-one-compound combinatorial libraries of peptide and peptoid ligands. The approach uses a cleavable linker that is hydrophilic to help reduce nonspecific binding to biological samples and allows for the attachment of a halogen tag, which greatly facilitates post-screening sequencing by tandem mass spectrometry (MS/MS). The linker is based on a tartaric acid unit, which, upon cleavage from resin, generates a C-terminal aldehyde. This aldehyde can then be derivatized with a bromine-containing amino-oxy compound that serves as an isotope tag for subsequent MS/MS analysis of y-ion fragments. We have applied this linker and method to the syntheses of a number of peptoids that vary in sequence and length and have also demonstrated single-bead sequencing of a peptoid pentamer. The linker is also shown to have very low levels of nonspecific binding to proteins.     

几丁质合成酶抑制剂

几丁质合成酶是生物合成几丁质的关键物质。几丁质是昆虫表皮和真菌细胞壁的特征成分,由于存在的特殊性而成为农药、医药研发的独特靶标。几丁质合成酶抑制剂由于具有安全、高效等特点,成为农用杀虫、杀螨、杀菌剂以及医药抗真菌药物的研发热点。本文综述了天然及人工合成的几丁质合成酶抑制剂的研究进展,并对其发展趋势进行了展望。     

pK(a) Switching induced by the change in the pi-conjugated system based on photochromism

Two diarylethene derivatives 1 a and 2 a containing a 2,5-diaryl-3-thienyl group have been designed and synthesized. The pK(a) values of these compounds change upon photoirradiation. They have a phenol group as a proton source and a pyridinium group as an acceptor unit at each end of the pi-conjugated chain. The cyclization/cycloreversion reactions can be used to control the length of the pi-conjugated chain between the proton source and the acceptor. The change in the pi-conjugated chain length caused the pK(a)-switching.     

Synthesis of bisubstrate analogues targeting alpha-1,3-fucosyltransferase and their activities

We designed two bisubstrate analogues targeting alpha-1,3-fucosyltransferases, based on the three dimensional structure of Lewis X, which is the product of a alpha-1,3-fucosyltransferase reaction. We selected guanosine-5'-diphospho-L-galactose as a donor mimic and 2-hydroxyethyl beta-D-galactoside as an acceptor mimic, and tethered these two mimics with a methylene or ethylene linker. For the synthesis, the 6-position of L-galactose and the 6-position of D-galactose were first tethered via a methylene or ethylene linker. The L-galactose moiety was then converted to a GDP derivative. Both bisubstrate analogues were moderate inhibitors against alpha-1,3-fucosyltransferase V and VI. The fact that they were substrates of alpha-1,3-fucosyltransferase VI suggested that these compounds bound to the donor binding site, but not to the acceptor binding site.     

Synthesis and cytotoxicity studies of artemisinin derivatives containing lipophilic alkyl carbon chains

[reaction: see text] Cytotoxic artemisinin derivatives have been synthesized by a modular approach of "artemisinin + linker + lipophilic alkyl carbon chain". A strong correlation between the length of the carbon chains and the cytotoxicities against human hepatocellular carcinoma (HepG2) was revealed. Notably, compared with artemisinin (IC(50) = 97 microM), up to 200-fold more potent cytotoxicity (IC(50) = 0.46 microM) could be achieved by attachment of a C(14)H(29) carbon chain to artemisinin via an amide linker.     

Differential effects of bromination on substrates and inhibitors of kynureninase from Pseudomonas fluorescens

A series of brominated compounds has been synthesized and evaluated as substrates and inhibitors of kynureninase from Pseudomonas fluorescens. Both 3-bromo-L-kynurenine and 5-bromo-L-kynurenine were found to be substrates with similar k(cat) values to L-kynurenine, but the K(m) value for 3-bromo-L-kynurenine is very high (ca. 2 mM) compared to that for 5-bromo-L-kynurenine (11 microM) and L-kynurenine (25 microM). Both isomers of bromokynurenine react with kynureninase within the dead time of the stopped-flow instrument (ca. 1 ms) to form quinonoid intermediates with a lambda max of 494 nm that decay with rate constants of 300-600 s-1, similar to L-kynurenine. The two diastereomers of 5-bromodihydro-L-kynurenine were also prepared, and are more potent inhibitors than dihydro-L-kynurenines. (4R)-5-Bromodihydro-L-kynurenine is one of the most potent inhibitors of P. fluorescens kynureninase found to date (Ki = 55 nM) and also acts as a slow substrate; the (4S)-epimer, on the other hand, shows no measurable substrate activity, but it is a potent competitive inhibitor with a Ki value of 170 nM. In contrast, brominated analogs of (S)-(2-aminophenyl)-L-cysteine S,S-dioxide, (S)-(2-amino-4-bromophenyl)-L-cysteine S,S-dioxide and (S)-(2-amino-5-bromophenyl)-L-cysteine S,S-dioxide are competitive inhibitors of kynureninase, with Ki values of about 300 and 400 nm, respectively, about ten-fold higher than the value of 27 nM obtained for the parent compound. These results suggest that the binding modes of substrates and the various classes of inhibitors in the active site of kynureninase are different.     

Synthesis of a Fucosylated Trisaccharide Via Transglycosylation by α-<Emphasis Type="SmallCaps">l</Emphasis>-Fucosidase from <Emphasis Type="Italic">Thermotoga maritima</Emphasis>

Fucosylated oligosaccharides, such as 2′-fucosyllactose in human milk, have important biological functions such as prebiotics and preventing infection. In this work, the effect of an acceptor substrate (lactose) and the donor substrate 4-nitrophenyl-α-l-fucopyranoside (pNP-Fuc) on the synthesis of a fucosylated trisaccharide was studied in a transglycosylation reaction using α-l-fucosidase from Thermotoga maritima. Conducting a matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS), it was demonstrated that synthesized oligosaccharide corresponded to a fucosylated trisaccharide, and high-performance liquid chromatography (HPLC) of the hydrolyzed compound confirmed it was fucosyllactose. As the concentration of the acceptor substrate increased, the concentration and synthesis rate of the fucosylated trisaccharide also increased, and the highest concentration obtained was 0.883 mM (25.2% yield) when using the higher initial lactose concentration (584 mM). Furthermore, the lower donor/acceptor ratio had the highest synthesis, so at the molar ratio of 0.001, a concentration of 0.286 mM was obtained (32.5% yield).     

Synthesis and evaluation of macrocyclic transition state analogue inhibitors for alpha-chymotrypsin

Lactams 1 and 2 are readily formed from acyclic precursors in the presence of trypsin and chymotrypsin, respectively, identifying the macrocyclic ring system as a potential motif for constrained transition state analogue inhibitors of the serine peptidases. Ketone 3 was synthesized and shown to be a modest inhibitor of chymotrypsin (Ki = 220 microM), albeit 4-fold more potent than the acyclic hydroxy acid 25 (Ki = 1.5 mM as a mixture of epimers). A precursor (31) to the amino boronic acid 4 was also prepared; although this derivative was a potent inhibitor of chymotrypsin (Ki = 130 nM) by virtue of the boronic acid moiety, it showed no advantage over the des-amino analogue 32 (Ki = 120 nM), which is not capable of cyclizing.     

Side chain engineering and conjugation enhancement of benzodithiophene and phenanthrenequnioxaline based conjugated polymers for photovoltaic devices

A series of donor‐acceptor conjugated polymers incorporating benzodithiophene (BDT) as donor unit and phenanthrenequnioxaline as acceptor unit with different side chains have been designed and synthesized. For polymer P1 featuring the BDT unit and alkoxy chains substituted phenanthrenequnioxaline unit in the backbone, serious steric hindrance resulted in quite low molecular weight. The implementation of thiophene ring spacer in polymer P2 greatly suppressed the interannular twisting to extend the effective conjugation length and consequently gave rise to improved absorption property and device performance. In addition, utilizing the alkylthienyl side chains to replace the alkyl side chains at BDT unit in polymer P3 further enhanced the photovoltaic performance due to the increased conjugation length. For polymer P4, translating the alkoxy side chains at the phenanthrenequnioxaline ring into the alkyl side chains at thiophene linker group enhanced molecular planarity and strengthened π?π stacking. Consequently improved absorption property and increased hole mobility were achieved for polymer P4. Our results indicated that side chain engineering not only can influence the solubility of polymer but also can determine the polymer backbone planarity and hence the photovoltaic properties. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 1915–1926     

First preparation of a novel polyol resin for purifying arylboronic acids

A novel polystyrene-supported triol resin was first prepared by reaction of the Merrifield resin with trometamol.Using this resin, arylboronic acids were efficiently isolated and purified through a "capture-release" procedure in organic solvents.However,in basic aqueous solvents arylboronic acids were immobilized on the resin only with low yield.