Synthesis of tetrakis(multifluoro-4-pyridyl)porphin derivatives as acetylcholinesterase inhibitors

New tetrakis(multifluoro-4-pyridyl)porphin derivatives (2-4) and water soluble porphyrin (5) were synthesized to investigate their interactions with acetylcholinesterase from electric eel. These compounds have been found to be the potent reversible inhibitors of the enzyme with Ki values of microM range. In addition, porphyrin (5) showed broad spectrum of anticancer activities.

Synthesis of the quinoline-linked triazolopyrimidine analogues and their interactions with the recombinant tobacco acetolactate synthase

Acetolactate synthase (ALS) is the first common enzyme in the biosynthesis of L-leucine, L-isoleucine, and L-valine. Triazolopyrimidine sulfonamide (TP) is a mixed-type inhibitor of ALS with respect to both pyruvate and thiamine pyrophosphate. In this study, we synthesized new substituted quinoline-linked TP analogues and several TP analogues which contained either unsubstituted aminoquinolines or amino isoquinolines. In addition, we examined the interactions of both the wild-type and the sulfonylurea-resistant recombinant tobacco ALS enzymes in a highly pure and active form with the quinoline-linked TP analogues, respectively. The wild-type tobacco ALS was extremely sensitive to inhibition by the quinoline-linked TP analogues. In contrast, the mutant tobacco ALS was insensitive to both the quinoline-linked triazolopyrimidine and the sulfonylurea herbicides. The results indicate that the ability of the quinoline-linked TP analogues to inhibit ALS is highly sensitive to substitution at the ortho position (C-7) and to the position of the ring nitrogen around the sulfonamide functionality (C-8).

Soluble overexpression in Escherichia coli, and purification and characterization of wild-type recombinant tobacco acetolactate synthase

Acetolactate synthase (ALS) is the first common enzyme in the biosynthesis of L-leucine, L-isoleucine, and L-valine. The wild-type ALS gene from Nicotiana tabacum was cloned into the bacterial expression vector pGEX-2T. The resulting recombinant plasmid pGEX-ALS2 was used to transform Escherichia coli strain XL1-Blue, and the wild-type tobacco ALS (wALS) was expressed in the bacteria as a protein fused with glutathione S-transferase (GST). The fusion product GST-wALS was purified in a single step on a glutathione-Sepharose column. The purified GST-wALS was sensitive to a sulfonylurea herbicide, and was lost its sensitivity to end products, L-valine, L-leucine and L-isoleucine. These results suggest that the purified recombinant tobacco ALS was functionally active, and that the sulfonylureas may not bind to the feedback regulatory site on the plant ALS.

Detection, quantitation, and localization of bovine angiogenin by immunological assays

Bovine angiogenin (bAng) is a potent blood vessel inducing protein found in bovine serum and milk. Antisera have been raised against bAng. Western blot analysis for bAng indicated that the polyclonal antibody recognized bAng specifically, and no cross-reactivity with bovine RNase A, a protein homologous to bAng, was observed. The sandwich enzyme-linked immunosorbent assay for bAng was sensitive to 10 pg of bAng, and this assay was able to quantitate bAng in bovine serum (100-180 ng/mL) and milk (4-8 micrograms/mL). Strong positive immunohistochemical reactions were detected in alveolar cells, the secretion of alveolar cells and excretory ducts in sections of cow mammary gland, epithelial cells of visceral peritoneum and bile-duct in sections of cow liver, and epithelial cells and mucous glands in sections of cow gallbladder. These results suggest that epithelial cells and secretory cells are major sites of angiogenin synthesis.

Inhibition of the alpha-L-arabinofuranosidase III of Monilinia fructigena by 1,4-dideoxy-1,4-imino-L-threitol and 1,4-dideoxy-1,4-imino-L-arabinitol

1. 1,4-Dideoxy-1,4-imino-L-threitol was synthesized and the synthesis of 1,4-dideoxy-1,4-imino-L-arabinitol was improved. 2. Both compounds are competitive inhibitors of Monilinia fructigena alpha-L-arabinofuranosidase III, the additional hydroxymethyl group in the arabinitol contributing about 17.8 kj/mol (4.25 kcal/mol) to the Gibbs free energy of binding. 3. The affinities (1/Ki) of both compounds vary with pH in a classical bell-shaped way, the pKa value being that of the acid-catalytic group on the enzyme [5.9; Selwood & Sinnott (1988) Biochem. J. 254, 899-901] and the pKb values being those of the free inhibitors, 7.6 and 7.8 respectively. 4. On the basis of these and literature data we suggest that efficient inhibition of a glycosidase at its pH optimum by an appropriate iminoalditol will be found when the pKa of the iminoalditol is below that of the acid-catalytic group of the target enzyme.

Inhibition of cell wall-associated enzymes in vitro and in vivo with sugar analogs

Sugar analogs were used to study the inhibition of cell wall-associated glycosidases in vitro and in vivo. For in vitro characterization, cell walls were highly purified from corn (Zea mays L.) root cortical cells and methods were developed to assay enzyme activity in situ. Inhibitor dependence curves, mode of inhibition, and specificity were determined for three sugar analogs. At low concentrations of castanospermine (CAS), 2-acetamido-1,5-imino-1,2,5-trideoxy-d-glucitol, and swainsonine, these inhibitors showed competitive inhibition kinetics with beta-glucosidase, beta-GIcNAcase, and alpha-mannosidase, respectively. Swainsonine specifically inhibited alpha-mannosidase activity, and 2-acetamido-1,5-imino-1,2,5-trideoxy-d-glucitol specifically inhibited beta-N-acetyl-hexosamindase activity. However, CAS inhibited a broad spectrum of cell wall-associated enzymes. When the sugar analogs were applied to 2 day old corn seedlings, only CAS caused considerable changes in root growth and development. To ensure that the concentration of inhibitors used in vitro also inhibited enzyme activity in vivo, an in vivo method for measuring cell wall-associated activity was devised.

Inhibition of alpha-L-fucosidase by derivatives of deoxyfuconojirimycin and deoxymannojirimycin

Deoxyfuconojirimycin (1,5-dideoxy-1,5-imino-L-fucitol) is a potent, specific and competitive inhibitor (Ki 1 x 10(-8) M) of human liver alpha-L-fucosidase (EC 3.2.1.51). Six structural analogues of this compound were synthesized and tested for their ability to inhibit alpha-L-fucosidase and other human liver glycosidases. It is concluded that the minimum structural requirement for inhibition of alpha-L-fucosidase is the correct configuration of the hydroxy groups at the piperidine ring carbon atoms 2, 3 and 4. Different substituents in either configuration at carbon atom 1 (i.e. 1 alpha- and beta-homofuconojirimycins) and at carbon atom 5 may alter the potency but do not destroy the inhibition of alpha-L-fucosidase. The pH-dependency of the inhibition by these amino sugars suggests very strongly that inhibition results from the formation of an ion-pair between the protonated inhibitor and a carboxylate group in the active site of the enzyme. Deoxymannojirimycin (1,5-dideoxy-1,5-imino-D-mannitol) is also a more potent inhibitor of alpha-L-fucosidase than of alpha-D-mannosidase. This can be explained by viewing deoxymannojirimycin as beta-L-homofuconojirimycin lacking the 5-methyl group. Conversely, beta-L-homo analogues of fuconojirimycin can also be regarded as derivatives of deoxymannojirimycin. This has permitted deductions to be made about the structural requirements of inhibitors of alpha- and beta-D-mannosidases.

Structure-activity relationship of swainsonine. Inhibition of human alpha-mannosidases by swainsonine analogues

The inhibitory properties of a series of synthetic epimers and analogues of swainsonine towards the multiple forms of human alpha-mannosidases were studied in vitro and in cells in culture. Of the five epimers tested, only the 8a-epimer and 8,8a-diepimer of swainsonine were specific and competitive inhibitors (Ki values of 7.5 x 10(-5) and 2 x 10(-6) M respectively) of lysosomal alpha-mannosidases in vitro and induced storage of mannose-rich oligosaccharides in human fibroblasts in culture. The structures of these storage products indicated that processing alpha-mannosidases had also been inhibited. This was consistent with the observed inhibition in vitro of these enzymes by these compounds. In contrast, the 8-epimer, 1,8-diepimer and 2,8a-diepimer of swainsonine had no appreciable effect on any alpha-mannosidases. The corresponding open-chain analogues of swainsonine, namely 1,4-dideoxy-1,4-imino-D-mannitol, of the 8a-epimer, namely 1,4-dideoxy-1,4-imino-D-talitol, and of the 8,8a-diepimer, namely 1,4-dideoxy-1,4-imino-L-allitol, were weaker competitive inhibitors of lysosomal alpha-mannosidase, with Ki values of 1.3 x 10(-5), 1.2 x 10(-4) and 1.2 x 10(-4) M respectively. These analogues also proved less effective at inducing oligosaccharide accumulation and in disturbing glycoprotein processing. These compounds offer the opportunity to determine which alterations in the chirality of the swainsonine molecule affect its inhibitory specificity. A comparison of their biological activities has identified reagents that will be useful for studying steps in the biosynthesis and catabolism of glycoproteins and that may be of potential value in chemotherapy.

Change in specificity of glycosidase inhibition by N-alkylation of amino sugars

The synthetic amino sugar 1,4-dideoxy-1,4-imino-L-allitol (DIA) is a moderately good inhibitor of human liver alpha-D-mannosidases and a weak inhibitor of alpha-L-fucosidase, N-acetyl-beta-D-hexosaminidase and beta-D-mannosidase. Methylation of the ring nitrogen of DIA markedly decreases the inhibition of all the glycosidases except N-acetyl-beta-D-hexosaminidase. N-Benzylation of DIA essentially abolishes all inhibitory activity, except towards alpha-L-fucosidase, which is more strongly inhibited than by either DIA or N-methyl-DIA. This is the first report of a change of specificity of inhibition of a glycosidase inhibitor by substitution of the ring nitrogen.

Aminosugar derivatives as potential anti-human immunodeficiency virus agents

Recent data suggest that aminosugar derivatives which inhibit glycoprotein processing have potential anti-human immunodeficiency virus (HIV) activity. These inhibitory effects may be due to disruption of cell fusion and subsequent cell-cell transmission of the acquired immunodeficiency syndrome (AIDS) virus. Free virus particles able to bind CD4-positive cells are still produced in the presence of these compounds with only partial reduction of infectivity. We now report a method to score in parallel both the degree of antiviral activity and the effect on cell division of aminosugar derivatives. We find that (i) the compounds 1,4-dideoxy-1,4-imino-L-arabinitol and N-(5-carboxymethyl-1-pentyl)-1,5-imino-L-fucitol partially inhibit the cytopathic effect (giant cell formation, etc.) of HIV and yield of infectious virus; (ii) the compounds N-methyldeoxynojirimycin and N-ethyldeoxynojirimycin reduce the yield of infectious HIV by an order of four and three logarithms, respectively; and (iii) one compound, N-butyldeoxynojirimycin, of the 47 compounds previously screened reduces infectious viral particles by a logarithmic order greater than five at noncytotoxic concentrations. In addition, long-term growth of infected cells in the presence of N-butyldeoxynojirimycin gradually decreases the proportion of infected cells, leading to eventual elimination of HIV from culture. This result suggests that replication is associated with cytolysis. The ability to break the cycle of replication and reinfection has important implications in the chemotherapy of AIDS.

Inhibition of HIV replication by amino-sugar derivatives

The plant alkaloids castanospermine, dihydroxymethyldihydroxypyrrolidine and deoxynojirimycin have recently been shown to have potential anti-HIV activity [(1987) Proc. Natl. Acad. Sci. USA 84, 8120-8124; (1987) Nature 330, 74-77; (1987) Lancet i, 1025-1026]. They are thought to act by inhibiting alpha-glucosidase I, an enzyme involved in the processing of N-linked oligosaccharides on glycoproteins. We report here the relative efficacy of a spectrum of amino-sugar derivatives as inhibition of HIV cytopathicity. Several alpha-glucosidase inhibitors and alpha-fucosidase inhibitors were found to be active at concentrations which were non-cytotoxic.