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The alkylating warhead of the pancreatic cancer drug streptozotocin (SZN) contains an N-nitrosourea moiety constructed from Nω-methyl-l-arginine (l-NMA) by the multi-domain metalloenzyme SznF. The enzyme's central heme-oxygenase-like (HO-like) domain sequentially hydroxylates Nδ and Nω' of l-NMA. Its C-terminal cupin domain then rearranges the triply modified arginine to Nδ-hydroxy-Nω-methyl-Nω-nitroso-l-citrulline, the proposed donor of the functional pharmacophore. Here we show that the HO-like domain of SznF can bind Fe(II) and use it to capture O2, forming a peroxo-Fe2(III/III) intermediate. This intermediate has absorption- and Mossbauer-spectroscopic features similar to those of complexes previously trapped in f erritin-like d iiron o xidases and oxygenases (FDOs) and, more recently, the HO-like fatty acid oxidase UndA. The SznF peroxo-Fe2(III/III) complex is an intermediate in both hydroxylation steps, as shown by the concentration-dependent acceleration of its decay upon exposure to either l-NMA or Nδ-hydroxy-Nω-methyl-l-Arg (l-HMA). The Fe2(III/III) cluster produced upon decay of the intermediate has a small Mossbauer quadrupole splitting parameter, implying that, unlike the corresponding product states of many FDOs, it lacks an oxo-bridge. The subsequent decomposition of the product cluster to one or more paramagnetic Fe(III) species over several hours explains why SznF was previously purified and crystallographically characterized without its cofactor. Programmed instability of the oxidized form of the cofactor appears to be a unifying characteristic of the emerging superfamily of H O-like d iiron o xidases and oxygenases (HDOs).

Glycosidase inhibitors have shown great potential as pharmacological chaperones for lysosomal storage diseases. In light of this, a series of new cyclopentanoid &beta, galactosidase inhibitors were prepared and their inhibitory and pharmacological chaperoning activities determined and compared with those of lipophilic analogs of the potent &beta, 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 &ldquo, strategic&rdquo, hydroxyl group. New compounds have revealed highly promising activities with a range of &beta, galactosidase-compromised human cell lines and may serve as leads towards new pharmacological chaperones for GM1-gangliosidosis and Morquio B disease.

Three new thiodiketopiperazine derivatives, rostratazine A (1) , rostratazine B (2) and rostratazine C (3) along with exserohilone (4) and boydine A (5) were isolated and identified from the laboratory culture of Setosphaeria rostrata , an endophytic fungus obtained from the fresh asymptomatic leaf tissues of the medicinal plant Costus speciosus from Sri Lanka. The structures of compounds 1–3 were elucidated on the basis of detailed interpretation of 1D- and 2D- NMR data and comparison to known compounds. Compounds 1 – 5 were subjected to α-glucosidase inhibitory and porcine pancreatic alpha amylase inhibitory assays and 4 showed alpha–glucosidase inhibitory activity while 2 showed porcine pancreatic alpha amylase inhibitory activity.

N-Functionalized amino(hydroxymethyl)cyclopentanetriols are potent inhibitors of β-d-galactosidases and, for the first time, could be shown to act as pharmacological chaperones for GM1-gangliosidosis-associated lysosomal acid β-galactosidase thus representing a new structural type of pharmacological chaperones for this lysosomal storage disease.

By Morita-Baylis-Hillman reaction of 2,3-O-isopropylidene-D-glyceraldehyde with α,β-unsaturated carbonyl as well as hetero analogous carbonyl compounds such as acrylonitrile, suitable precursors of isofagomine and of 4-epi-isofagomine are available. Elaboration of the structures by amine introduction, followed by intramolecular ring closure and subsequent hydroboration of the double bond provides 4-epi-isofagomine derivatives featuring chain extensions at C-5a which are determined by the structures of the carbonyl compounds employed. As an example, the synthesis of C-(5aR)- and C-(5aS)-5a-C-pentyl-4-epi-isofagomines, powerful inhibitors of β-galactosidases, is outlined. In line with reported data, the (C-5aR) epimer was found a highly potent experimental pharmacological chaperone for GM1-associated human lysosomal β-galactosidase mutant R201C.

From 1,2;3,4-di-O-isopropylidene-α-D-galactopyranose, a series of highly functionalized (hydroxymethyl)cyclopentanes was easily available. In line with reports by Reymond and Jager on similar structures, these amine containing basic carbasugars are potent inhibitors of β-D-galactosidases and, for the first time, could be shown to act as pharmacological chaperones for GM1-gangliosidosis-associated lysosomal acid β-galactosidase mutant R201C, thus representing a new structural type of pharmacological chaperones for this lysosomal storage disease.

A series of N-alkyl derivatives of the D-galactosidase inhibitor 1,4-di-epi-validamine featuring lipophilic substituents at position C-5a was prepared and screened for their glycosidase inhibitory properties. Products turned out selective for β-galactosidases as well as β-glucosidases.

The iron-dependent oxidase UndA cleaves one C3–H bond and the C1–C2 bond of dodecanoic acid to produce 1-undecene and CO(2). A published x-ray crystal structure showed that UndA has a heme-oxygenase-like fold, thus associating it with a structural superfamily that includes known and postulated nonheme diiron proteins, but revealed only a single iron ion in the active site. Mechanisms proposed for initiation of decarboxylation by cleavage of the C3–H bond using a mono-iron cofactor to activate O(2) necessarily invoked unusual or potentially unfeasible steps. Here we present spectroscopic, crystallographic, and biochemical evidence that the cofactor of Pseudomonas fluorescens Pf-5 UndA is actually a diiron cluster and show that binding of the substrate triggers rapid addition of O(2) to the Fe(2)(II/II) cofactor to produce a transient peroxo-Fe(2)(III/III) intermediate. The observations of a diiron cofactor and substrate-triggered formation of a peroxo-Fe(2)(III/III) intermediate suggest a small set of possible mechanisms for O(2), C3–H and C1–C2 activation by UndA; these routes obviate the problematic steps of the earlier hypotheses that invoked a single iron.

Selective inhibitors of human pancreatic α-amylase (HPA) are an effective means of controlling blood sugar levels in the management of diabetes. A high-throughput screen of marine natural product extracts led to the identification of a potent (Ki = 10 pM) peptidic HPA inhibitor, helianthamide, from the Caribbean sea anemone Stichodactyla helianthus. Active helianthamide was produced in Escherichia coli via secretion as a barnase fusion protein. X-ray crystallographic analysis of the complex of helianthamide with porcine pancreatic α-amylase revealed that helianthamide adopts a β-defensin fold and binds into and across the amylase active site, utilizing a contiguous YIYH inhibitory motif. Helianthamide represents the first of a novel class of glycosidase inhibitors and provides an unusual example of functional malleability of the β-defensin fold, which is rarely seen outside of its traditional role in antimicrobial peptides., We describe the discovery and structural characterization of helianthamide, a peptide with highly potent and selective inhibitory activity against human pancreatic α-amylase.

Helianthamide is a potent inhibitor of human pancreatic α-amylase (HPA) (KI = 0.01 nM) produced by the Caribbean sea anemone Stichodactyla helianthus. Helianthamide was previously shown to be structurally homologous to the β-defensins and represents a new structural class of protein inhibitors of α-amylase. To understand the source of this potent inhibition, we performed site-directed mutagenesis studies on helianthamide fusion proteins. A novel YIYH inhibitory motif that interacts with conserved active site residues was originally proposed as being central to inhibitory activity based on the X-ray crystal structure of the porcine pancreatic α-amylase–helianthamide complex. However, variants in which these polar residues were replaced, individually, with alanine or phenylalanine bound only 5–46-fold more weakly than wild-type helianthamide, suggesting modest contributions from these interactions. In contrast, individual replacement of helianthamide’s six cysteine residues with alanine resulted in much lar...

The complex plant flavonol glycoside montbretin A is a potent (Ki = 8 nM) and specific inhibitor of human pancreatic α-amylase with potential as a therapeutic for diabetes and obesity. Controlled degradation studies on montbretin A, coupled with inhibition analyses, identified an essential high-affinity core structure comprising the myricetin and caffeic acid moieties linked via a disaccharide. X-ray structural analyses of the montbretin A-human α-amylase complex confirmed the importance of this core structure and revealed a novel mode of glycosidase inhibition wherein internal π-stacking interactions between the myricetin and caffeic acid organize their ring hydroxyls for optimal hydrogen bonding to the α-amylase catalytic residues D197 and E233. This novel inhibitory motif can be reproduced in a greatly simplified analog, offering potential for new strategies for glycosidase inhibition and therapeutic development.

N-Functionalized amino(hydroxymethyl)cyclopentanetriols are potent inhibitors of β-d-galactosidases and, for the first time, could be shown to act as pharmacological chaperones for G

From 1,2;3,4-di-O-isopropylidene-α-D-galactopyranose, a series of highly functionalized (hydroxymethyl)cyclopentanes was easily available. In line with reports by Reymond and Jäger on similar structures, these amine containing basic carbasugars are potent inhibitors of β-D-galactosidases and, for the first time, could be shown to act as pharmacological chaperones for G

Pathogenic fungi kill an estimated 1.3 million people each year. This number is predicted to rise as drug resistance spreads, thus antifungal drugs with novel modes of action are urgently required. Fungal endoglycoceramidase-related proteins 1 and 2 (EGCrP-1 and -2), which hydrolyse glucosylceramide and ergosteryl β-glucoside, respectively, are important for fungal cell growth and have been identified as potential targets for drug development. A library of iminosugar derivatives was screened against EGCrP-1 and -2, and a number of competitive inhibitors with nanomolar affinities were identified. In addition, a mechanism-based inhibitor was shown to form a covalent derivative with EGCrP-2. Nine of the inhibitors were evaluated against Cryptococcus neoformans. Several showed growth inhibitory activity, but only against a C. neoformans strain lacking the outer fungal polysaccharide capsule; this implies that penetration into the cell is a significant handicap for these inhibitors. Pro-drug versions of these inhibitors could address this issue.

Globoid cell leukodystrophy (GCL), or Krabbe disease, is a lysosomal storage disorder characterized by a deficiency in galactosylceramidase (GALC), which hydrolyses galactosylceramide and galactosylsphingosine (psychosine). Early detection of GCL in newborns is essential for timely therapeutic intervention and could be achieved by testing infant blood samples with isotopically labeled lysosmal enzyme substrates and mass spectrometry. While isotopically labeled psychosine would be a useful tool for the early diagnosis of GCL, its synthesis is lengthy and expensive. To obviate this problem we developed a one-step chemoenzymatic synthesis of psychosine using a glycosynthase mutant of the Rhodococcus equi endogalactosylceramidase (EGALC), α-D-galactopyranosyl fluoride and sphingosine.

From an easily available partially protected analog of 1-deoxy-L-gulo-nojirimycin, by chain-branching at C-4 and suitable modification, lipophilic analogs of the powerful β-D-galactosidase inhibitor 4-epi-isofagomine have been prepared. New compounds exhibit considerably improved inhibitory activities when compared with the unsubstituted parent compound and may serve as leads toward new pharmacological chaperones for GM1-gangliosidosis and Morquio B disease.

The scope of a one-pot tandem approach for the synthesis of C-1 alkyl iminoalditol derivatives with a Staudinger/aza-Wittig/Grignard cascade has been evaluated. The reaction conditions have been optimized for two azidodeoxy aldose substrates and a range of Grignard reagents. The nature of both, substrate as well as nucleophile, was found to control the stereoselectivity of the alkyl addition to the cyclic iminium intermediate at position C-1. This approach enabled the synthesis of a collection of C-alkyl iminoalditols, which were biologically evaluated as inhibitors against a set of standard glycoside hydrolases. All compounds were found to exhibit highly selective inhibition of β-glucosidase activity.

A highly divergent route to lipophilic iminosugars that utilizes the thiol-ene reaction was developed to enable the rapid synthesis of a collection of 16 dideoxyiminoxylitols bearing various different lipophilic substituents. Enzyme kinetic analyses revealed that a number of these products are potent, low-nanomolar inhibitors of human glucocerebrosidase that stabilize the enzyme to thermal denaturation by up to 20 K. Cell based assays conducted on Gaucher disease patient derived fibroblasts demonstrated that administration of the compounds can increase lysosomal glucocerebrosidase activity levels by therapeutically relevant amounts, as much as 3.2-fold in cells homozygous for the p.N370S mutation and 1.4-fold in cells homozygous for the p.L444P mutation. Several compounds elicited this increase in enzyme activity over a relatively wide dosage range. The data assembled here illustrate how the lipophilic moiety common to many glucocerebrosidase inhibitors might be used to optimize a lead compound's ability to chaperone the protein in cellulo. The flexibility of this synthetic strategy makes it an attractive approach to the rapid optimization of glycosidase inhibitor potency and pharmacokinetic behavior.

A new Staudinger/aza Wittig/Strecker multicomponent reaction sequence to C-1-cyano iminoalditols has been developed. When applied to 5-azidodeoxy-d-xylose and -d-glucose as substrates the method leads smoothly in good yield and with excellent stereoselectivity to respectively, 1,5-dideoxy-1,5-imino-d-idurono nitrile and 2,6-didesoxy-2,6-imino-d-glycero-d-ido-heptononitrile.

Mechanism-based inhibitors are relatively chemically inert compounds that become activated when processed by their target enzyme, leading to covalent enzyme inactivation. Fluorine substitution confers a number of properties that are beneficial to the chemistry of such inhibitors and to their potential use as pharmaceuticals, and indeed several fluorinated mechanism-based inhibitors have made it to clinical usage over the past 50 years. Well-known examples are the 5- fluorouracil metabolite, 5-fluoro-2'-deoxyuridine-5'-monophosphate, which is used in the treatment of cancer, and α- difluoromethylornithine for the treatment of African sleeping sickness. As the prevalence of fluorine in medicinal chemistry continues to rise, more and more medically relevant fluorinated mechanism-based inhibitors are being developed with a variety of interesting properties and uses.