Synthesis of l-[4-11 C]Asparagine by Ring-Opening Nucleophilic 11 C-Cyanation Reaction of a Chiral Cyclic Sulfamidate Precursor.

The development of a convenient and rapid method to synthesize radiolabeled, enantiomerically pure amino acids (AAs) as potential positron emission tomography (PET) imaging agents for mapping various biochemical transformations in living organisms remains a challenge. This is especially true for the synthesis of carbon-11-labeled AAs given the short half-life of carbon-11 (11 C, t1/2 =20.4 min). A facile synthetic pathway to prepare enantiomerically pure 11 C-labeled l-asparagine was developed using a partially protected serine as a starting material with a four-step transformation providing a chiral five-membered cyclic sulfamidate as the radiolabeling precursor. Its structure and absolute configuration were confirmed by X-ray crystallography. Utilizing a [11 C]cyanide nucleophilic ring opening reaction followed by selective acidic hydrolysis and deprotection, enantiomerically pure l-[4-11 C]asparagine was synthesized. Further optimization of reaction parameters, including base, metal ion source, solvent, acid component, reaction temperature and reaction time, a reliable two-step method for synthesizing l-[4-11 C]asparagine was presented: within a 45±3 min (n=5, from end-of-bombardment), the desired enantiomerically pure product was synthesized with the initial nucleophilic cyanation yield of 69±4 % (n=5) and overall two-step radiochemical yield of 53±2 % (n=5) based on starting [11 C]HCN, and with radiochemical purity of 96±2 % (n=5).

Characterization of a Salmonella sugar kinase essential for the utilization of fructose-asparagine.

Salmonella can utilize fructose-asparagine (F-Asn), a naturally occurring Amadori product, as its sole carbon and nitrogen source. Conversion of F-Asn to the common intermediates glucose-6-phosphate, aspartate, and ammonia was predicted to involve the sequential action of an asparaginase, a kinase, and a deglycase. Mutants lacking the deglycase are highly attenuated in mouse models of intestinal inflammation owing to the toxic build-up of the deglycase substrate. The limited distribution of this metabolic pathway in the animal gut microbiome raises the prospects for antibacterial discovery. We report the biochemical characterization of the kinase that was expected to transform fructose-aspartate to 6-phosphofructose-aspartate during F-Asn utilization. In addition to confirming its anticipated function, we determined through studies of fructose-aspartate analogues that this kinase exhibits a substrate-specificity with greater tolerance to changes to the amino acid (including the d-isomer of aspartate) than to the sugar.

Total Syntheses of Cystobactamids and Structural Confirmation of Cystobactamid 919-2.

The cystobactamids are a family of antibacterial natural products with unprecedented chemical scaffolds that are active against both Gram-positive and Gram-negative pathogens. Herein, we describe the first total synthesis of cystobactamid 919-2 from three fragments. Our convergent synthesis enabled both the confirmation of the correct structure and the determination of the absolute configuration of cystobactamid 919-2.

Chemical synthesis of asparagine-linked archaeal N-glycan from Methanothermus fervidus.

Several N-linked glycoproteins have been identified in archaea and there is growing evidence that the N-glycan is involved in survival and functioning of archaea in extreme conditions. Chemical synthesis of the archaeal N-glycans represents a crucial step towards understanding the putative function of protein glycosylation in archaea. Herein the first total synthesis of the archaeal L-asparagine linked hexasaccharide from Methanothermus fervidus is reported using a highly convergent [3+3] glycosylation approach in high overall yields. The synthesis relies on efficient preparation of regioselectively protected thioglycoside building blocks for orthogonal glycosylations and late stage N-aspartylation.

Cystobactamids: myxobacterial topoisomerase inhibitors exhibiting potent antibacterial activity.

The development of new antibiotics faces a severe crisis inter alia owing to a lack of innovative chemical scaffolds with activities against Gram-negative and multiresistant pathogens. Herein, we report highly potent novel antibacterial compounds, the myxobacteria-derived cystobactamids 1-3, which were isolated from Cystobacter sp. and show minimum inhibitory concentrations in the low µg mL(-1) range. We describe the isolation and structure elucidation of three congeners as well as the identification and annotation of their biosynthetic gene cluster. By studying the self-resistance mechanism in the natural producer organism, the molecular targets were identified as bacterial type IIa topoisomerases. As quinolones are largely exhausted as a template for new type II topoisomerase inhibitors, the cystobactamids offer exciting alternatives to generate novel antibiotics using medicinal chemistry and biosynthetic engineering.

A facile synthesis of α-N-ribosyl-asparagine and α-N-ribosyl-glutamine building blocks.

Adenosine diphosphate ribosylation (ADP-ribosylation) is a widely occurring post-translational modification of proteins at nucleophilic side chain of amino acid residues. Elucidation of ADP-ribosylation events would benefit greatly from the availability of well-defined ADP-ribosylated peptides and analogues thereof. In this paper we present a novel approach to the chemical synthesis of ribosylated amino acid building blocks using traceless Staudinger ligation. We describe an efficient and stereoselective synthesis of α-N-ribosyl-asparagine (α-N-ribosyl-Asn) and α-N-ribosyl-glutamine (α-N-ribosyl-Gln) building blocks starting from 5-tert-butyldiphenylsilyl-ß-D-ribofuranosyl azide. The N-glycosyl aminoacids are produced in good yields as pure α-anomers, suitably protected for peptide synthesis.

[Oral dietary supplements with copper, magnesium, manganese and zinc-based new complexes]. / Suplementos nutricionales orales a base de nuevos complejos de cobre, magnesio, manganeso y zinc.

Oligoelements such as copper, magnesium, manganese and zinc are involved in several metabolic, enzymatic and immunological processes. They are also important for the integral tissue proteins and could be involved in gene expression regulation. The deficiency of these essential elements hampers the appropriate function of the body and may cause various diseases. Therefore, it is important to guarantee the incorporation of these trace elements in the diet, but the quantity provided is not always adequate for the optimum body performance. Currently, conventional nutritional supplements have two major problems. The first one is attributed to the association of inorganic salts with metals which might cause low absorption and gastric intolerance. The second problem is caused when several metals are present in a formulation which could lead to possible antagonistic interactions. For this reason, this study explores the development of cations (i.e., copper, zinc, magnesium and manganese) and amino acids (i.e., glycine and asparagine) new complexes formulated into compacts for oral administration. In each reaction, ligands were linked to non-antagonistic cation pairs. The complex formation was characterized by infrared spectroscopy, differential scanning calorimetry, thermogravimetric analysis and powder X-ray diffraction analyses. Compact disintegration and in-vitro dissolution tests for these complexes were also determined.

Synthesis of orthogonally protected L-threo-beta-ethoxyasparagine.

Orthogonally protected L-threo-beta-ethoxyasparagine (Fmoc-EtOAsn(Trt)-OH, 1) was synthesized from diethyl (2S,3S)-2-azido-3-hydroxysuccinate 2 in eight steps as a building block for solid-phase peptide synthesis. The starting material is easily available in multi-gram scale from D-diethyltartrate. The transformation steps reported here are robust and scalable. Thus, a significant amount of 1 (1.8 g) was obtained in 21% overall yield. The synthesis reported is also expected to be useful for the preparation of other O-substituted L-threo-beta-hydroxyasparagine derivatives.

Efficient synthesis and enzymatic extension of an N-GlcNAz asparagine building block.

N-Azidoacetyl-d-glucosamine (GlcNAz) is a particularly useful tool in chemical biology as the azide is a metabolically stable yet accessible handle within biological systems. Herein, we report a practical synthesis of FmocAsn(N-Ac3GlcNAz)OH, a building block for solid phase peptide synthesis (SPPS). Protecting group manipulations are minimised by taking advantage of the inherent chemoselectivity of phosphine-mediated azide reduction, and the resulting glycosyl amine is employed directly in the opening of Fmoc protected aspartic anhydride. We show potential application of the building block by establishing it as a substrate for enzymatic glycan extension using sugar oxazolines of varying size and biological significance with several endo-ß-N-acetylglucosaminidases (ENGases). The added steric bulk resulting from incorporation of the azide is shown to have no or a minor impact on the yield of enzymatic glycan extension.

New chemistry with old functional groups: on the reaction of isonitriles with carboxylic acids--a route to various amide types.

Thermolysis of isonitriles with carboxylic acids provides, in one step, N-formyl imides (see, for example, 8 + 19 --> 21). The resultant N-formyl group can be converted to N-H, NCH2OH, or NCH3. This chemistry allows for a new route for synthesizing beta-N (asparagine)-linked glycosyl amino acids.

Cyclic thioanhydrides: linchpins for multicomponent coupling reactions based on the reaction of thioacids with electron-deficient sulfonamides and azides.

Reaction of cyclic thioanhydrides with amines affords amides functionalized with thioacids, which can be trapped in situ with electron-deficient azides or, preferably, 2,4-dinitrobenzenesulfonamides. In this manner the cyclic thioanhydride serves as a linchpin in a three-component coupling sequence. The use of thiomaleic anhydride and a bifunctional nucleophile extends the process to heterocycle synthesis, while a cyclic thioanhydride prepared from aspartic acid directly provides N-functionalized asparagine derivatives.

Synthesis and analgesic activities of endomorphin-2 and its analogues.

Endomorphin-2 (1; H-Tyr-Pro-Phe-Phe-NH2; EM2) and its novel cyclic asparagine (cycloAsn) analogues, H-Tyr-cAsn(CHPh)-Phe-Phe-NH2 (2) and H-Tyr-cAsn(CHMe2)-Phe-Phe-NH2 (3), were synthesized via liquid-phase synthesis. The structures of the products and intermediates were characterized by IR, 1H-NMR, MS, and HR-MS analyses. The antinociceptive activity of EM2 and its cyclic asparagine analogues were assessed in AcOH-induced abdominal constriction tests in mice with i.p. injection. The results show that the antinociceptive activities of EM2 and its cyclic asparagine analogue 2 were higher than those of aspirine and meperidine. Analogue 2 was observed to be a stronger analgesic with dose-dependence than EM2. The test mice did not show any tendency to be addicted while administrated of analogue 2 repeatedly and regularly.

N-phosphonacetyl-L-isoasparagine a potent and specific inhibitor of Escherichia coli aspartate transcarbamoylase.

The synthesis of a new inhibitor, N-phosphonacetyl-L-isoasparagine (PALI), of Escherichia coli aspartate transcarbamoylase (ATCase) is reported, as well as structural studies of the enzyme.PALI complex. PALI was synthesized in 7 steps from beta-benzyl L-aspartate. The KD of PALI was 2 microM. Kinetics and small-angle X-ray scattering experiments showed that PALI can induce the cooperative transition of ATCase from the T to the R state. The X-ray structure of the enzyme.PALI complex showed 22 hydrogen-bonding interactions between the enzyme and PALI. The kinetic characterization and crystal structure of the ATCase.PALI complex also provides detailed information regarding the importance of the alpha-carboxylate for the binding of the substrate aspartate.

Highly regioselective synthesis of a 3-O-sulfonated arabino Lewis(a) asparagine building block suitable for glycopeptide synthesis.

Using the stannylene method, the trisaccharide 2-acetamido-3-O-[6-O-benzyl-beta-D-galactopyranosyl]-4-O-[2,3,4-tri-O-benzyl-beta-D-arabinopyranosyl]-6-O-benzyl-2-deoxy-beta-D-glucopyranosyl azide was regioselectively sulfonated and, after reduction of the anomeric azide, coupled to Fmoc alpha-allyl aspartate. After Pd(0)-catalyzed deallylation, the sulfatyl Lewis(a) asparagine building block was obtained, suitable for solid-phase glycopeptide synthesis applying the fluoride labile PTMSEL linker system.

Synthesis of glycosyl amino acids by light-induced coupling of photoreactive amino acids with glycosylamines and 1-C-aminomethyl glycosides.

The glycosylamines of O-acetyl-protected GlcNAc and chitobiose, as well as two partially unprotected 1-C-aminomethyl glucosides, were photochemically coupled with orthogonally protected N-aspartyl-5-bromo-7-nitroindoline derivatives. The reactions proceeded under neutral conditions by irradiation with near-UV light. The glycosyl asparagines with N- or C-glycosyl linkages were afforded in 60-85% yield on a 10-70 mg scale. Moreover, the ability of a highly photoreactive N-glutamyl-4-methoxy-7-nitroindoline derivative to acylate amino saccharides was tested. Upon irradiation in the presence of a dimeric 1-C-aminomethyl glycoside, or a glycosylamine, the corresponding glycosyl glutamines were obtained in 50% and 30% yield, respectively. Preparations of the photoreactive aspartates and the 1-C-aminomethyl glycosides are also described.

DL-threo-beta-Fluoroaspartate and DL-threo-beta-fluoroasparagine: selective cytotoxic agents for mammalian cells in culture.

Absolute configuration assignments have been made for the diastereomers of DL-beta-fluoroaspartate by X-ray analysis. The cytotoxicity of these isomers against various mammalian cells was examined. DL-threo-beta-Fluoroaspartate shows selective cytotoxicity. Growth of the most sensitive cells is completely inhibited by 13 micrometers DL-threo-beta-fluoroaspartate in the presence of 100 micrometers L-aspartate, a component of the culture medium. A difference in the rate of transport of DL-beta-fluoroaspartate among the cells studied is an important factor determining cell specificity. For those cells that are sensitive to DL-beta-fluoroaspartate, the threo isomer is, in all cases, more potent than the erythro isomer. Radioactivity derived from L-threo-beta-fluoro[14C]aspartate is incorporated into proteins at a rate comparable to the rate of incorporation from L-[14C]aspartate. We synthesized DL-threo-beta-fluoroasparagine. This compound is also cytotoxic but less specific and less potent than DL-threo-beta-fluoroaspartate. However, the cell specificity can be enhanced in the presence of 1 mM L-aspartate, which can protect some cells but not others from the cytotoxic effects of DL-threo-beta-fluoroasparagine. Jensen sarcoma cells, which require asparagine, are not protected by L-aspartate. Therefore, a combination of L-aspartate and DL-threo-beta-fluroasparagine can be used to inhibit specifically the growth of asparagine-requiring tumors.

Potential carcinostatics. Synthesis and biological properties of d- and 1-beta,beta-difluoroaspartic acid and beta,beta-difluoroasparagine.

Di-tert-butyl beta,beta-difluorooxaloacetate, prepared by fluorination of di-tert-butyl oxaloacetate with perchloryl fluoride, was converted to di-tert-butyl beta,beta-difluoroaspartate via its O-methyl oxime, followed by reduction. The tert-butyl ester was hydrolyzed to give a mixture of dl-beta,beta-difluoroaspartic acid, which was resolved via its brucine salts. dl-Difluoroaspartic acid was converted into beta,beta-difluoroasparagine by monoesterification and subsequent ammonolysis. Racemic beta,beta-difluoroaspartic acid inhibits aspartate aminotransferase. Cell growth of 3T3-F cells was slightly inhibited by l-beta,beta-difluoraspartic acid while the d enantiomer was without effect in this test system.

Potential inhibitors of L-asparagine biosynthesis. 4. Substituted sulfonamide and sulfonylhydrazide analogues of L-asparagine.

Several N-substituted sulfonamides and N'-substituted sulfonylhydrazides have been prepared as sulfur analogues of L-asparagine with the potential of acting as inhibitors of L-asparagine synthetase (ASase, from Novikoff hepatoma). L-Cysteine was converted in known steps to N-carboxy-3-(sulfonylchloro)-L-alanine dibenzyl ester (1). Condensation of 1 with O-benzylhydroxylamine, p-(fluorosulfonyl)benzylamine, or monoethyl fumarylhydrazide (9), followed by deblocking with HF, gave 3-(hydroxysulfamoyl)-L-alanine (3a), 3-[p-(fluorosulfonylbenzyl)]sulfamoyl-L-alanine (3c), and 3-sulfo-L-alanine S-[2-[(E)-3-(ethoxycarbonyl)acryloyl]hydrazide] (3e), respectively. Similarly, 1 with 2-chloroethylamine and deblocking with H2-Pd gave 3-[(2-chloroethyl)sulfamoyl]-L-alanine (3b). tert-Butyl carbazate was allowed to react with 1 and the tert-butyl group was removed with HCl. The resulting sulfonylhydrazide 7 was condensed with p-(fluorosulfonyl)benzoyl chloride and then deblocked with HF to give 3-sulfo-L-alanine S-[2-[P-(fluorosulfonyl)benzoyl]hydrazide] (3d). The inhibition of ASase by 3a-e at 2 mM was 97, 0, 30, 43, and 37%, respectively, and 3a was competitive with L-aspartic acid. Neither 3a nor 3e was effective in increasing the life span of mice bearing P-388 lymphocytic leukemia.

Active-site studies of neurohypophyseal hormones: synthesis and pharmacological properties of [5-(N4,N4-dimethylasparagine)]oxytocin.

Synthesis and biological properties of [5-(N4,N4-dimethylasparagine)]oxytocin are reported. In this analogue, the hydrogens of the primary carboxamide moiety in the side chain of the asparagine residue in position 5 of the posterior pituitary hormone oxytocin have been replaced by two methyl groups. The protected nonapeptide intermediate was prepared by a stepwise procedure using solution techniques. The analogue possesses 4.60 +/- 0.03 units/mg (mean +/- SEM) uterotonic activity on the isolated rat uterine horn and 9.14 +/- 0.03 units/mg of avian vasodepressor activity. Moreover, it displays an identical intrinsic activity in the in vitro rat uterotonic assay as oxytocin, when tested in the presence of either 0.5 mM Ca2+ (standard assay conditions) or at reduced levels of Ca2+ (0.3, 0.15, and 0.05 mM). This result is significant in view of the proposed biologically active model of oxytocin, in which the side chain of the 5 position residue was assigned to contain an "active element" responsible for the intrinsic activity of the hormone when bound to the uterine receptor.

Design and synthesis of a series of (2R)-N(4)-hydroxy-2-(3-hydroxybenzyl)-N(1)- [(1S,2R)-2-hydroxy-2,3-dihydro-1H-inden-1-yl]butanediamide derivatives as potent, selective, and orally bioavailable aggrecanase inhibitors.

A pharmacophore model of the P1' site, specific for aggrecanase, was defined using the specificity studies of the matrix metalloproteinases and the similar biological activity of aggrecanase and MMP-8. Incorporation of the side chain of a tyrosine residue into compound 1 as the P1' group provided modest selectivity for aggrecanase over MMP-1, -2, and -9. A cis-(1S)(2R)-amino-2-indanol scaffold was incorporated as a tyrosine mimic (P2') to conformationally constrain 2. Further optimization resulted in compound 11, a potent, selective, and orally bioavailable inhibitor of aggrecanase.