Synthesis of a precursor of D-fagomine by immobilized fructose-6-phosphate aldolase

Fructose-6-phosphate aldolase (FSA) is an important enzyme for the C-C bond-forming reactions in organic synthesis. The present work is focused on the synthesis of a precursor of D-fagomine catalyzed by a mutant FSA. The biocatalyst has been immobilized onto several supports: magnetic nanoparticle clusters (mNC), cobalt-chelated agarose (Co-IDA), amino-functionalized agarose (MANA-agarose) and glyoxal-agarose, obtaining a 29.0%, 93.8%, 89.7% and 53.9% of retained activity, respectively. Glyoxal-agarose FSA derivative stood up as the best option for the synthesis of the precursor of D-fagomine due to the high reaction rate, conversion, yield and operational stability achieved. FSA immobilized in glyoxal-agarose could be reused up to 6 reaction cycles reaching a 4-fold improvement in biocatalyst yield compared to the non-immobilized enzyme.

Mechanistic Insights into the Chaperoning of Human Lysosomal-Galactosidase Activity: Highly Functionalized Aminocyclopentanes and C-5a-Substituted Derivatives of 4-epi-Isofagomine

Glycosidase inhibitors have shown great potential as pharmacological chaperones for lysosomal storage diseases. In light of this, a series of new cyclopentanoid β-galactosidase inhibitors were prepared and their inhibitory and pharmacological chaperoning activities determined and compared with those of lipophilic analogs of the potent β-d-galactosidase inhibitor 4-epi-isofagomine. Structure-activity relationships were investigated by X-ray crystallography as well as by alterations in the cyclopentane moiety such as deoxygenation and replacement by fluorine of a “strategic” hydroxyl group. New compounds have revealed highly promising activities with a range of β-galactosidase-compromised human cell lines and may serve as leads towards new pharmacological chaperones for G_M1-gangliosidosis and Morquio B disease.

Bioevaluation of sixteen ADMDP stereoisomers toward alpha-galactosidase A: Development of a new pharmacological chaperone for the treatment of Fabry disease and potential enhancement of enzyme replacement therapy efficiency

A unique molecular library consisting of all sixteen synthetic ADMDP (1-aminodeoxy-DMDP) stereoisomers has been prepared and evaluated for inhibitory activity against α-Gal A, and ability to impart thermal stabilization of this enzyme. The results of this testing led us to develop a novel pharmacological chaperone for the treatment of Fabry disease. 3-Epimer ADMDP was found to be an effective pharmacological chaperone, able to rescue α-Gal A activity in the lymphoblast of the N215S Fabry patient-derived cell line, without impairment of cellular β-galactosidase activity. When 3-epimer ADMDP was administered with rh-α-Gal A (enzyme replacement therapy) for the treatment of Fabry patient-derived cell lines, improvements in the efficacy of rh-α-Gal A was observed, which suggests this small molecule can also provide clinical benefit of enzyme replacement therapy in Fabry disease.

Evaluation of fluoropyruvate as nucleophile in reactions catalysed by N-acetyl neuraminic acid lyase variants: scope, limitations and stereoselectivity

The catalysis of reactions involving fluoropyruvate as donor by N-acetyl neuraminic acid lyase (NAL) variants was investigated. Under kinetic control, the wild-type enzyme catalysed the reaction between fluoropyruvate and N-acetyl mannosamine to give a 90 : 10 ratio of the (3R,4R)- and (3S,4R)-configured products; after extended reaction times, equilibration occurred to give a 30 : 70 mixture of these products. The efficiency and stereoselectivity of reactions of a range of substrates catalysed by the E192N, E192N/T167V/S208V and E192N/T167G NAL variants were also studied. Using fluoropyruvate and (2R,3S)- or (2S,3R)-2,3-dihydroxy-4-oxo-N,N-dipropylbutanamide as substrates, it was possible to obtain three of the four possible diastereomeric products; for each product, the ratio of anomeric and pyranose/furanose forms was determined. The crystal structure of S. aureus NAL in complex with fluoropyruvate was determined, assisting rationalisation of the stereochemical outcome of C-C bond formation.

Combined inhibitor free-energy landscape and structural analysis reports on the mannosidase conformational coordinate

Mannosidases catalyze the hydrolysis of a diverse range of polysaccharides and glycoconjugates, and the various sequence-based mannosidase families have evolved ingenious strategies to overcome the stereoelectronic challenges of mannoside chemistry. Using a combination of computational chemistry, inhibitor design and synthesis, and X-ray crystallography of inhibitor/enzyme complexes, it is demonstrated that mannoimidazole-type inhibitors are energetically poised to report faithfully on mannosidase transition-state conformation, and provide direct evidence for the conformational itinerary used by diverse mannosidases, including β-mannanases from families GH26 and GH113. Isofagomine-type inhibitors are poor mimics of transition-state conformation, owing to the high energy barriers that must be crossed to attain mechanistically relevant conformations, however, these sugar-shaped heterocycles allow the acquisition of ternary complexes that span the active site, thus providing valuable insight into active-site residues involved in substrate recognition.

Chemical synthetic biology

Although both the most popular form of synthetic biology (SB) and chemical synthetic biology (CSB) share the biotechnologically useful aim of making new forms of life, SB does so by using genetic manipulation of extant microorganism, while CSB utilises classic chemical procedures in order to obtain biological structures which are non-existent in nature. The main query concerning CSB is the philosophical question: why did nature do this, and not that? The idea then is to synthesise alternative structures in order to understand why nature operated in such a particular way. We briefly present here some various examples of CSB, including those cases of nucleic acids synthesised with pyranose instead of ribose, and proteins with a reduced alphabet of amino acids; also we report the developing research on the "never born proteins" (NBP) and "never born RNA" (NBRNA), up to the minimal cell project, where the issue is the preparation of semi-synthetic cells that can perform the basic functions of biological cells.

Solution and gas-phase H/D exchange of protein-small-molecule complexes: Cex and its inhibitors

The properties of noncovalent complexes of the enzyme exo-1,4-β-D-glycanase ("Cex") with three aza-sugar inhibitors, deoxynojirimycin (X(2)DNJ), isofagomine lactam (X(2)IL), and isofagomine (X(2)IF), have been studied with solution and gas-phase hydrogen deuterium exchange (H/Dx) and measurements of collision cross sections of gas-phase ions. In solution, complexes have lower H/Dx levels than free Cex because binding the inhibitors blocks some sites from H/Dx and reduces fluctuations of the protein. In mass spectra of complexes, abundant Cex ions are seen, which mostly are formed by dissociation of complexes in the ion sampling interface. Both complex ions and Cex ions formed from a solution containing complexes have lower cross sections than Cex ions from a solution of Cex alone. This suggests the Cex ions formed by dissociation "remember" their solution conformations. For a given charge, ions of the complexes have greater gas-phase H/Dx levels than ions of Cex. Unlike cross sections, H/Dx levels of the complexes do not correlate with the relative gas-phase binding strengths measured by MS/MS. Cex ions from solutions with or without inhibitors, which have different cross sections, show the same H/Dx level after 15 s, indicating the ions may fold or unfold on the seconds time scale of the H/Dx experiment. Thus, cross sections show that complexes have more compact conformations than free protein ions on the time scale of ca. 1 ms. The gas-phase H/Dx measurements show that at least some complexes retain different conformations from the Cex ions on a time scale of seconds.

[Study on chemical constituents of Peganum multisectum]

OBJECTIVE

To study the chemical consituents of Peganum multisectum.

METHODS

The compounds were isolated by chromatographic methods and their structures were elucidated by physicochemical properties and spectral analysis.

RESULTS

Six alkaloids were isolated and identifiedas deoxyvasicinone (1), l-vasicinone (2), harmine (3), vasicine (4), evodiamin (5), and fagomine (6).

CONCLUSION

Compounds 5 and 6 are isolated from this genus for the first time.

Effects of pH and iminosugar pharmacological chaperones on lysosomal glycosidase structure and stability

Human lysosomal enzymes acid-beta-glucosidase (GCase) and acid-alpha-galactosidase (alpha-Gal A) hydrolyze the sphingolipids glucosyl- and globotriaosylceramide, respectively, and mutations in these enzymes lead to the lipid metabolism disorders Gaucher and Fabry disease, respectively. We have investigated the structure and stability of GCase and alpha-Gal A in a neutral-pH environment reflective of the endoplasmic reticulum and an acidic-pH environment reflective of the lysosome. These details are important for the development of pharmacological chaperone therapy for Gaucher and Fabry disease, in which small molecules bind mutant enzymes in the ER to enable the mutant enzyme to meet quality control requirements for lysosomal trafficking. We report crystal structures of apo GCase at pH 4.5, at pH 5.5, and in complex with the pharmacological chaperone isofagomine (IFG) at pH 7.5. We also present thermostability analysis of GCase at pH 7.4 and 5.2 using differential scanning calorimetry. We compare our results with analogous experiments using alpha-Gal A and the chaperone 1-deoxygalactonijirimycin (DGJ), including the first structure of alpha-Gal A with DGJ. Both GCase and alpha-Gal A are more stable at lysosomal pH with and without their respective iminosugars bound, and notably, the stability of the GCase-IFG complex is pH sensitive. We show that the conformations of the active site loops in GCase are sensitive to ligand binding but not pH, whereas analogous galactose- or DGJ-dependent conformational changes in alpha-Gal A are not seen. Thermodynamic parameters obtained from alpha-Gal A unfolding indicate two-state, van't Hoff unfolding in the absence of the iminosugar at neutral and lysosomal pH, and non-two-state unfolding in the presence of DGJ. Taken together, these results provide insight into how GCase and alpha-Gal A are thermodynamically stabilized by iminosugars and suggest strategies for the development of new pharmacological chaperones for lysosomal storage disorders.

[Alkaloid constituents from silkworm dropping of Bombyx mori]

OBJECTIVE

To extract and isolate chemical constituents from the total alkaloids of silkworm dropping (Can Sha) of Bombyx mori L.

METHODS

Chemical constituents were isolated by column chromatography with macroporous adsorbent resin, ion-exchange resin and sephadex LH 20. The structures of the isolated compounds were determined by spectral means.

RESULTS

Three compounds were isolated and identified as 1-deoxynojirimycin (1) , fagomine (2) , and 3-epifagomine (3) on the basis of their 1H-NMR, 13C-NMR spectra and ESIMS data.

CONCLUSION

Compounds 1-3 are isolated and identified from Can Sha for the first time.

Stereocontrolled Access to Orthogonally Protected anti,anti-4-Aminopiperidine-3,5-diols through Chemoselective Reduction of Enantiopure β-Lactam Cyanohydrins

The cyanosilylation of enantiopure 4-oxoazetidine-2-carbaldehydes with tert-butyldimethylsilyl cyanide was promoted by either molecular sieves or catalytic amount of sodium carbonate to give O-silylated beta-lactam cyanohydrins with good yield and diastereoselectivity. In contrast, Lewis acids did not effectively promote the cyanosilylation under different experimental conditions, and instead hydrocyanation took place affording the corresponding free cyanohydrins in variable yield and selectivity. Starting from beta-lactam cyanohydrin hybrids, two concise, complementary stereocontrolled routes to optically pure orthogonally protected anti,anti-4-amino-3,5-piperidine diols were achieved. Key features of the first approach include chemoselective reductive opening of the beta-lactam ring with LiBH4 to a 3-amino-5-hydroxy pentanenitrile followed by reductive cyclization of a conveniently functionalized cyanomesylate derivative with NaBH4/NiCl2. The second approach involves LiAlH4 reduction of protected anti,anti-4-amino-3,5-dihydroxypiperidin-2-ones, which were easily obtained by chemoselective reduction of the cyano group in the beta-lactam cyanohydrin hybrids with NaBH4/NiCl2 and subsequent intramolecular rearrangement of the resulting amino beta-lactams. Both routes make use of an oxidative N-dearylation with diacetoxyiodobenzene of a 4-methoxyphenylamino group as a common synthetic step. Specifically, the utility of this novel reaction sequence has been demonstrated by the synthesis of fully orthogonally protected sialidase inhibitors.

[Chemical constituents from leaves of Morus multicaulis]

OBJECTIVE

To study the chemical constituents from the leaves of Morus multicaulis.

METHOD

The compounds were isolated by ion exchange resin, silica gel and Sephadex LH -20 column chromatographies. Their structures were elucidated on the basis of physico-chemical properties and spectral data.

RESULT

Twelve compounds were isolated from the leaves of this plant. Their structures were identified as 1-deoxynojirimycin (1), fagomine (2), 2-O-alpha-D-galactopyranosyl-1-deoxynojirimycin (3), quercetin-7-O-beta-D-glucoside (4), kaempferol (5), quercetin (6), scopoletin (7), D-aspartic acid (8), L-proline (9), D-alpha-alanine (10), myo-inositol (11) and dausterol (12).

CONCLUSION

All compounds were isolated from this plant for the first time.

Structure of acid beta-glucosidase with pharmacological chaperone provides insight into Gaucher disease

Gaucher disease results from mutations in the lysosomal enzyme acid beta-glucosidase (GCase). Although enzyme replacement therapy has improved the health of some affected individuals, such as those with the prevalent N370S mutation, oral treatment with pharmacological chaperones may be therapeutic in a wider range of tissue compartments by restoring sufficient activity of endogenous mutant GCase. Here we demonstrate that isofagomine (IFG, 1) binds to the GCase active site, and both increases GCase activity in cell lysates and restores lysosomal trafficking in cells containing N370S mutant GCase. We also compare the crystal structures of IFG-bound GCase at low pH with those of glycerol-bound GCase at low pH and apo-GCase at neutral pH. Our data indicate that IFG induces active GCase, which is secured by interactions with Asn370. The design of small molecules that stabilize substrate-bound conformations of mutant proteins may be a general therapeutic strategy for diseases caused by protein misfolding and mistrafficking.

Fructose-6-phosphate Aldolase in Organic Synthesis: Preparation ofd-Fagomine,N-Alkylated Derivatives, and Preliminary Biological Assays

[Structure: see text] D-fructose-6-phosphate aldolase (FSA) mediates a novel straightforward two-step chemo-enzymatic synthesis of D-fagomine and some of its N-alkylated derivatives in 51% isolated yield and 99% de. The key step is the FSA-catalyzed aldol addition of simple dihydroxyacetone (DHA) to N-Cbz-3-aminopropanal. The use of FSA greatly simplifies the enzymatic procedures that used dihydroxyacetonephosphate or DHA/esters. Some N-alkyl derivatives synthesized elicited antifungal and antibacterial activity as well as enhanced inhibitory activity, and selectivity against beta-galactosidase and alpha-glucosidase.

Tandem Staudinger-azaWittig mediated ring expansion: rapid access to new isofagomine-tetrahydroxyazepane hybrids

New seven-membered iminosugars with potent and selective inhibition towards glycosidases have been prepared as 1-N-iminosugar homologues via a tandem Staudinger-azaWittig mediated ring expansion.

Palladium-Catalyzed DYKAT of Butadiene Monoepoxide: Enantioselective Total Synthesis of (+)-DMDP, (−)-Bulgecinine, and (+)-Broussonetine G

Palladium catalyzed asymmetric allylic alkylation reaction of an amine with two equivalents of butadiene monoxide allows for the expedient synthesis of trans- and cis-2,5-dihydropyrroles. The versatility of these chiral synthons towards the synthesis of a wide variety of iminosugar natural products was demonstrated with the short and high yielding asymmetric syntheses of (+)-DMDP, and (-)-bulgecinine. In addition, the first total synthesis of (+)-broussonetine G, a potent glycosidase inhibitor, is described along with the assignment of its relative and absolute stereochemical configuration.

Synthesis and Biological Evaluation of Glycosidase Inhibitors: gem-Difluoromethylenated Nojirimycin Analogues

In our ongoing program aimed at the design, synthesis, and biological evaluation of novel gem-difluoromethylenated glycosidase inhibitors, gem-4,4-difluoromethylenated iminosugars (5-9) were synthesized. The biological evaluation of these synthetic iminosugars showed that the gem-difluoromethylenyl group generally reduced the inhibition of glycosidases. However, this was not the case at pH 5.0, where the gem-difluoromethylenated iminosugar 6 was a stronger inhibitor than comparable iminosugars 1 and 36, suggesting that the influence of this group is mainly through its effect on the amine. It is proposed that the unprotonated iminosugar is the species preferably bound by beta-glucosidase, due to the lower pK(a) value of iminosugar 6 than of 1 or 36, leaving iminosugars 1 and 36 mostly protonated at pH 5.0, while iminosugar 6 is not. Iminosugar 6 also displayed good and selective inhibition of beta-glucosidase at pH 6.8.

Novel five-membered iminocyclitol derivatives as selective and potent glycosidase inhibitors: new structures for antivirals and osteoarthritis

A novel 5-membered iminocyclitol derivative was found to be a potent and selective inhibitor of the glycoprotein-processing alpha-glucosidase with a Ki value of 53 nM. This compound was further derivatized to antiviral agents against Japanese encephalitis virus, dengue virus serotype 2 (DEN-2), human SARS coronavirus, and human beta-hexosaminidase (Ki = 2.6 nM), a new target for the development of osteoarthritis therapeutics.

Intramolecular Benzyl Protection Delivery: A Practical Synthesis of DMDP and DGDP from d-Fructose

[reaction: see text] A two-step protection of 1,2-diols as the corresponding o-xylylene cyclic ethers, involving an intramolecular ring-closing O-benzylation reaction, has been developed to overcome the problems associated to regioselective benzylation reactions. The strategy has been applied to the high-yielding synthesis of the pyrrolidine glycosidase inhibitors DMDP and DGDP.

Looking glass inhibitors: efficient synthesis and biological evaluation of d-deoxyfuconojirimycin

1,6-Dideoxygalactostatin, the mirror image of 1-deoxy-L-fuconojirimycin, was efficiently prepared from 2,3-O-isopropylidene-L-lyxonolactone in four steps and evaluated as a glycosidase inhibitor.

Highly Stereocontrolled Synthesis of gem-Difluoromethylenated Azasugars: d- and l-1,4,6-Trideoxy-4,4-difluoronojirimycin

[reaction: see text]. D-1,4,6-trideoxy-4,4-difluoronojirimycin and L-1,4,6-trideoxy-4,4-difluoronojirimycin, a novel series of gem-4,4-difluoromethylenated azasugars, were synthesized from CF3CH2OH in 10 steps. A key step was the highly diastereoselective construction of the piperidine ring via reductive amination.

Synthesis and evaluation of the glycosidase inhibitory activity of 5-hydroxy substituted isofagomine analogues

An efficient strategy for the synthesis of 5-hydroxy substituted isofagomine analogues and , having both -CH2OH/CH3 and -OH functionality at the C-5 position, and evaluation of their inhibitory potency is reported. The synthetic methodology involves the aldol-Cannizzaro reaction of easily available alpha-d-xylopentodialdose followed by hydrogenolysis to afford the triol . Selective amidation of the alpha- and beta-hydroxymethyl group at C-4, deprotection of the 1,2-acetonide group and hydrogenation gave the target molecules, which were found to be potent against beta-glycosidases with IC50 values in the micro molar range. Compound showed excellent potency against glycosidases and human salivary amylase.