Structural analysis of a new glycosphingolipid from the lipopolysaccharide-lacking bacterium Sphingomonas adhaesiva.

A new glycosphingolipid, GSL-4B, was isolated from Sphingomonas adhaesiva and found to share the ceramide moiety with GSL-1 and GSL-3 from Sphingomonas capsulata studied earlier [Kawahara, K.; Moll, H.; Knirel, Y. A.; Seydel, U.; Z?hringer, U. Eur. J. Biochem. 2000, 267, 1837-1846]. It is heterogeneous with respect to the long-chain bases erythro-2-amino-1,3-octadecanediol (sphinganine), (13Z)-erythro-2-amino-13-eicosene-1,3-diol, and (13Z)-erythro-2-amino-13,14-methylene-1,3-eicosanediol which in GSL-4B are present in the ratios of 1.1:1.0:1.1, and all bearing amide-linked (S)-2-hydroxymyristic acid. Methylation analysis and MALDI-TOF-MS along with 1H and 13C NMR spectroscopy showed that the carbohydrate part of GSL-4B has the structure of alpha-D-Glcp-(1-->4)-alpha-D-Galp-(1-->6)-alpha-D-Glcp-(1-->4)-alpha-D-GlcpA-(1-->1)-Cer     

2-aminohydroxamic acid derivatives as inhibitors of Bacillus cereus phosphatidylcholine preferred phospholipase C PC-PLC(Bc)

Phosphatidylcholine preferring phospholipase C (PC-PLC) is an important enzyme that plays a key role in a variety of cellular events and lipid homoeostases. Bacillus cereus phospholipase C (PC-PLC(Bc)) has antigenic similarity with the elusive mammalian PC-PLC, which has not thus far been isolated and purified. Therefore the discovery of inhibitors of PC-PLC(Bc) is of current interest. Here, we describe the synthesis and biological evaluation of a new type of compounds inhibiting PC-PLC(Bc). These compounds have been designed by evolution of previously described 2-aminohydroxamic acid PC-PLC(Bc) inhibitors that block the enzyme by coordination of the zinc active site atoms present in PC-PLC(Bc) [Gonzalez-Roura, A.; Navarro, I.; Delgado, A.; Llebaria, A.; Casas, J. Angew. Chem. Int. Ed.2004, 43, 862]. The new compounds maintain the zinc coordinating groups and possess an extra trimethylammonium function, linked to the hydroxyamide nitrogen by an alkyl chain, which is expected to mimic the trimethylammonium group of the phosphatidylcholine PC-PLC(Bc) substrates. Some of the compounds described inhibit the enzyme with IC(50)'s in the low micromolar range. Unexpectedly, the most potent inhibitors found are those that possess a trimethylammonium group but have chemically blocked the zinc coordinating functionalities. The results obtained suggest that PC-PLC(Bc) inhibition is not due to the interaction of compounds with the phospholipase catalytic zinc atoms, but rather results from the inhibitor cationic group recognition by the PC-PLC(Bc) amino acids involved in choline lipid binding.     

Synthesis of 2',3'-dideoxy-2'-fluoro-3'-thioarabinothymidine and its 3'-phosphoramidite derivative

An efficient method for the synthesis of 5'-O-monomethoxytrityl-2',3'-dideoxy-2'-fluoro-3'-thioarabinothymidine [(5'MMT)araF-T(3'SH), (5)] and its 3'-phosphoramidite derivative (6) suitable for automated incorporation into oligonucleotides, is demonstrated. A key step in the synthesis involves reaction of 5'-O-MMT-2,3'-O-anhydrothymidine (4) (Eleuteri, A.; Reese, C.B.; Song, Q. J. Chem. Soc. Perkin Trans. 1 1996, 2237 pp.) with sodium thioacetate to give (5'-MMT)araF-T(3'SAc) (5) (Elzagheid, M.I.; Mattila, K.; Oivanen, M.; Jones, B.C.N.M.; Cosstick, L?nnberg, H. Eur. J. Org. Chem. 2000, 1987-1991). This nucleoside was then converted to its corresponding phosphoramidite derivative, 6, as described previously ((a) Sun, S.; Yoshida, A.; Piccirilli, J.A. RNA, 1997, 3, 1352-1363; (b) Matulic-Adamic, J.; Beigelman, L. Helvetica Chemica Acta 1999, 82, 2141-2150: (c) Fettes, K.J.; O'Neil, I.; Roberts, S.M.; Cosstick, R. Nucleosides, Nucleotides and Nucl. Acids 2001, 20, 1351-1354).     

Synthesis of bisaminoacylated pdCpAs and tandemly activated transfer RNAs

Described herein is the preparation of new bisacylated tRNAs and their participation in protein synthesis. It has been reported that Thermus thermophilus phenylalanyl-tRNA synthetase can introduce two phenylalanine moieties onto the 3'-terminal adenosine of its cognate tRNA. It is also possible to prepare bisactivated tRNAs in vitro; these participate in protein synthesis [Wang, B.; Zhou, J.; Lodder, M.; Anderson, R. D.; Hecht, S. M. J. Biol. Chem.2006, 281, 13865]. Presently, the chemical strategy used for the synthesis of the key intermediate bisacylated pdCpAs is described. Bis-S-alanyl- and bis-S-methionyl-pdCpAs were prepared initially. Further, S-threonine, S-allo-threonine, S-homoserine, and (S)-(+)-2-amino-3-hydroxy-3-methylbutyric acid were coupled with the dinucleotide to define preparative methods applicable to more complex amino acids bearing additional functionality in the form of an OH group.     

A new concept for DNA-arrays

We will insert a cleavage site in an oligodeoxynucleotide, which can be used for a selective and quantitative cleavage. For that reason we synthesized the four 5'-S-(4,4'-dimethoxytrityl)-mercapto-2'-deoxynucleotide-3'-O-(2-cyanoethoxydiisopropylamino)-phosphites (5a-d). The cleavage of P-S and C-S bonds is described (Mag, M.; Lücking, S.; Engels, J.W. Synthesis and selective cleavage of an oligodeoxy-nucleotide containing a bridged internucleotide 5'-phosphorthioate linkage. Nucleic Acids Res. 1991, 19 (7), 1437-1441; Marriott, J.H.; Mottahedeh, M.; Reese, C.B. 9-(4-methoxyphenyl)xanthen-9-thiol: A useful reagent for the preparation of thiols. Tetrahedron Lett. 1990, 31 (51), 7485-7488; Divakar, K.J.; Mottoh, A.; Reese, C.B.; Shanghvi, Y.S. Approaches to the synthesis of 2' thio analogues of pyrimidine ribosides. J. Chem. Sc., Perkin Trans. 1 1990, 969-974). The oligodeoxynucleotides with an achiral bridged 5'-phosphorothioate linkage 5'-O-P-S-3' are synthesized by the phosphoramidite procedure.     

A re-examination of the difluoromethylenesulfonic acid group as a phosphotyrosine mimic for PTP1B inhibition

Protein tyrosine phosphatase 1B (PTP1B) is involved in the down-regulation of insulin signaling and is a well-validated therapeutic target for the treatment of diabetes and obesity. Key to the design of potent inhibitors of PTP1B is a moiety that effectively mimics the phosphate group of the natural phosphotyrosine substrate. Difluoromethylsulfonomethylphenylalanine (F(2)Smp) is one of the best monoanionic pTyr mimics reported to date. However, the difluoromethylenesulfonic acid (DFMS) group as a phosphate mimic has not been carefully evaluated in the context of a non-peptidyl platform. Here we present a careful examination of the DFMS group as a phosphate mimic. This was achieved by first constructing an analog of a previously reported high affinity, non-peptidyl PTP1B inhibitor (compound 2, IC(50)=8nM) in which a difluoromethylenephosphonic acid group is replaced with the DFMS moiety (compound 6). We also report the synthesis of its non-fluorinated methylenesulfonic analog (compound 7), as well as two other derivatives in which a distal sulfonamide moiety is replaced with a difluoromethylenesulfonamide group (compounds 8 and 9). Compounds 2 and 6-9 were examined as PTP1B inhibitors. Replacing the distal sulfonamide moiety with a difluoromethylenesulfonamide group had only a modest effect on inhibitor potency. However, compound 6 was approximately a 1000-fold poorer inhibitor than compound 2. Most significantly, inhibition studies with compound 7 and a peptide bearing sulfonomethylphenylalanine revealed that the fluorines have little effect on the potency of the DFMS-bearing inhibitors. This is in contrast to a previous assumption that the fluorines in DFMS-bearing inhibitors contributed significantly to their potency. This may in part explain the large difference in potency between the DFMS and DFMP-bearing compounds. These results also demonstrate that sulfonomethylphenylalanine, a pTyr mimic that is readily constructed, is a relatively good pTyr mimic in comparison to most others that have been reported when examined in the context of the DADE-X-LNH(2) peptide platform.     

Structural characterization of the acid-degraded secondary cell wall polymer of Geobacillus stearothermophilus PV72/p2

The secondary cell wall polymer (SCWP) from Geobacillus stearothermophilus PV72/p2, which is involved in the anchoring of the surface-layer protein to the bacterial cell wall layer, is composed of 2-amino-2-deoxy- and 2-acetamido-2-deoxy-D-glucose, 2-acetamido-2-deoxy-D-mannose, and 2-acetamido-2-deoxy-D-mannuronic acid. The primary structure of the acid-degraded polysaccharide--liberated by HF-treatment from the cell wall--was determined by high-field NMR spectroscopy and mass spectrometry using N-acetylated and hydrolyzed polysaccharide derivatives as well as Smith-degradation. The polysaccharide was shown to consist of a tetrasaccharide repeating unit containing a pyruvic acid acetal at a side-chain 2-acetamido-2-deoxy-alpha-D-mannopyranosyl residue. Substoichiometric substitutions of the repeating unit were observed concerning the degree of N-acetylation of glucosamine residues and the presence of side-chain linked 2-acetamido-2-deoxy-beta-D-glucopyranosyl units: [Formula: see text].     

Further studies on hepatitis C virus NS5B RNA-dependent RNA polymerase inhibitors toward improved replicon cell activities: benzimidazole and structurally related compounds bearing the 2-morpholinophenyl moiety

Following the discovery of JTK-109 (1) as a potent inhibitor of hepatitis C virus NS5B RNA-dependent RNA polymerase, [(a) Hirashima, S.; Suzuki, T.; Ishida, T.; Noji, S.; Yata, S.; Ando, I.; Komatsu, M.; Ikeda, S.; Hashimoto, H. J. Med. Chem.2006, 49, 4721. (b) Hashimoto, H.; Mizutani, K.; Yoshida, A. Int. Patent Appl. WO 01/47883, 2001.] further studies toward the improvement of the cellular potency have been performed. A greater than 40-fold improvement was achieved through replacing the biphenyl moiety with a 2-morpholinophenyl group and the benzimidazole ring with the tetracyclic scaffold to afford compound 7 with an excellent replicon potency (EC(50)=7.6 nM).     

Structural elucidation of the lipopolysaccharide core region of the O-chain-deficient mutant strain A28 from Pseudomonas aeruginosa serotype 06 (International Antigenic Typing Scheme).

The lipopolysaccharide (LPS) of the Pseudomonas aeruginosa serotype 06 rough-type mutant A28 was isolated by a modified phenol-chloroform-petroleum ether extraction method. Deoxycholate-polyacrylamide gel electrophoresis indicated a single band with mobility similar to that of the complete core region of the wild-type parent serotype 06 (International Antigenic Typing Scheme) strain. Compositional analysis of the LPS indicated that the core oligosaccharide was composed of D-glucose (three units), L-rhamnose (one unit), 2-amino-2-deoxy-D-galactose (one unit), L-glycero-D-manno-heptose (two units), 3-deoxy-D-manno-octulosonic acid (two units), L-alanine (one unit), and phosphate (two units). Under the mild conditions of hydrolysis with methanolic hydrogen chloride, a 7-O-carbamoyl substituent was observed on the second heptose residue. The glycan structure of the LPS was determined by employing one- and two-dimensional nuclear magnetic resonance spectroscopy and mass spectrometry-based methods with a backbone oligosaccharide that was obtained from the LPS by deacylation, dephosphorylation, and reduction of the terminal glucosamine. On the basis of the results of the present study and our earlier work with the P. aeruginosa 06-derived core-defective mutant R5 (H. Masoud, E. Altman, J. C. Richards, and J. S. Lam, Biochemistry, 33:10568-10578, 1994), a structural model for the complete core oligosaccharide is proposed.     

The design and synthesis of a potent Angiotensin II cyclic analogue confirms the ring cluster receptor conformation of the hormone Angiotensin II

The novel amide linked Angiotensin II potent cyclic analogue, c-[Sar1,Lys3,Glu5] ANG II 19 has been designed and synthesized in an attempt to test the aromatic ring clustering and the charge relay bioactive conformation we have recently suggested for ANG II. This constrained cyclic analogue was synthesized by connecting the Lys3 amino and Glu5 carboxyl side chain groups, and it was found to be potent in the rat uterus assay and in anesthetized rabbits. The central part of the molecule is fixed covalently in the conformation predicted according to the backbone bend conformational model proposed for Angiotensin II. The obtained results using a combination of 2D NMR, 1D NOE spectroscopy and molecular modeling revealed a similar Tyr4-Ile5-His6 bend, a His6-Pro7 trans configuration and a side chain aromatic ring cluster of the key aminoacids Tyr4, His6, Phe8 for c-[Sar1,Lys3,Glu5] ANG II as it has been found for ANG II (Matsoukas, J. H.; Hondrelis, J.; Keramida, M.; Mavromoustakos, T.; Markriyannis, A.; Yamdagni, R.; Wu, Q.; Moore, G. J. J. Biol. Chem. 1994, 269, 5303). Previous study of the conformational properties of the Angiotensin II type I antagonist [Hser(gamma-OMe)8] ANG II (Matsoukas, J. M.; Agelis, G.; Wahhab, A.; Hondrelis, J.; Panagiotopoulos. D.; Yamdagni, R.; Wu, Q.; Mavromoustakos, T.; Maia, H.; Ganter, R.; Moore, G. J. J. Med. Chem. 1995, 38, 4660) using 1-D NOE spectroscopy coupled with the present study of the same type of lead antagonist Sarilesin revealed that the Tyr4-Ile5-His6 bend, a conformational property found in Angiotensin II is not present in type I antagonists. The obtained results provide an important conformational difference between Angiotensin II agonists and type I antagonists. It appears that our synthetic attempt to further support our proposed model was successful and points out that the charge relay system and aromatic ring cluster are essential stereoelectronic features for Angiotensin II to exert its biological activity.     

2,3-Ethylene- and 2,3-trimethylene-bridged analogues of the group III metabotropic glutamate receptor ligand 2-amino-4-phosphonobutanoic acid

The racemic trans- and cis-isomers of 1-amino-2-phosphonomethyl-cyclobutanecarboxylic acid (5 and 6) and 1-amino-2-phosphonomethyl-cyclopentanecarboxylic acid (7 and 8) were synthesized as extensions of the mGluR4 agonists trans- and cis-1-amino-2-phosphonomethyl-cyclopropanecarboxylic acid (3 and 4). Although the methylene bridge in 3 and 4 allows for retention of affinity toward the mGluR4 receptor, increasing the bridging unit to the ethylene group as in 5 and 6 or to the trimethylene group as in 7 and 8 introduces sufficient steric hindrance to eliminate affinity for the mGluR4 receptor.     

A New Concept for DNA-Arrays

Abstract

We will insert a cleavage site in an oligodeoxynucleotide, which can be used for a selective and quantitative cleavage. For that reason we synthesized the four 5′-S-(4,4′-dimethoxytrityl)-mercapto-2′-deoxynucleotide-3′-O-(2-cyanoethoxydiisopropylamino)-phosphites ( 5a–d ). The cleavage of P-S and C-S bonds is described (Mag, M.; Lücking, S.; Engels, J.W. Synthesis and selective cleavage of an oligodeoxy-nucleotide containing a bridged internucleotide 5′-phosphorthioate linkage Nucleic Acids Res. 1991, 19 (7), 1437–1441; Marriott, J.H.; Mottahedeh, M.; Reese, C.B. 9-(4-methoxyphenyl)xanthen-9-thiol: A useful reagent for the preperation of thiols. Tetrahedron Lett. 1990, 31 (51), 7485–7488; Divakar, K.J.; Mottoh, A.; Reese, C.B.; Shanghvi, Y.S. Approaches to the synthesis of 2′ thio analogues of pyrimidine ribosides. J. Chem. Sc., Perkin Trans. 1 1990, 969–974). The oligodeoxynucleotides with an achiral bridged 5′-phosphorothioate linkage 5′-O-P-S-3′ are synthesized by the phosphoramidite procedure.     

Structural studies of the O-specific side-chains of the shigella sonnei phase I lipopolysaccharide

The structure of the O-specific side-chains of the Shigella sonnei phase I lipopolysaccharide has been investigated. The side chains are composed of disaccharide repeating-units containing two uncommon sugar components, one of witch, 2-amino-2-deoxy-L-altruronic acid, has been identified previously. The other has now been identified as 2-acetamido-4-amino-2,4,6-trideoxy-D-galactose. The uronic acid, as N-acetylated α-pyranosyl residues, is linked through O-4, and the diamino sugar, as β-pyranosyl residues, is linked through O-3. The pyranosyluronic acid residue assumes the ⁴C₁ conformation in the polymer, with the carboxyl group in the axial position.     

Identification of 2-amino-6-O-(2-amino-2-deoxy-beta-D-glucopyranosyl)-2-deoxy-D-glucose as a major constituent of the hydrophobic region of the Bordetella pertussis endotoxin

2-Amino-6-O-(2-amino-2-deoxy-β- d-glucopyranosyl)-2-deoxy- d-glucose substituted on the amino group of the reducing 2-amino-2-deoxy- d-glucose unit by a 3-hydroxytetradecanoyl group was shown to be a major constituent of the “Lipid A” fragment obtained by acid hydrolysis of the Bordetella pertussis endotoxin.     

Thiazole- and selenazole-comprising high-affinity inhibitors possess bright microsecond-scale photoluminescence in complex with protein kinase CK2

A previously disclosed protein kinase (PK) CK2-selective inhibitor 4-(2-amino-1,3-thiazol-5-yl)benzoic acid (ATB) and its selenium-containing counterpart (ASB) revealed remarkable room temperature phosphorescence when bound to the ATP pocket of the protein kinase CK2. Conjugation of these fragments with a mimic of CK2 substrate peptide resulted in bisubstrate inhibitors with increased affinity towards the kinase. Attachment of the fluorescent acceptor dye 5-TAMRA to the conjugates led to significant enhancement of intensity of long-lifetime (microsecond-scale) photoluminescence of both sulfur- and selenium-containing compounds. The developed photoluminescent probes make possible selective determination of the concentration of CK2 in cell lysates and characterization of CK2 inhibitors by means of time-gated measurement of photoluminescence.     

Structure and immunochemistry of an oligosaccharide repeating unit of the capsular polysaccharide of type III group B Streptococcus. A revised structure for the type III group B streptococcal polysaccharide antigen

We have derived oligosaccharides from the capsular polysaccharide of type III group B Streptococcus by enzymatic hydrolysis of a specific backbone glycosidic bond utilizing an endo-beta-galactosidase from Flavobacterium keratolyticus. Enzymatic digestion of the polysaccharide produced oligosaccharide fragments of one or more pentasaccharide repeating units. On the basis of 13C NMR, 1H NMR, and methylation analyses, it was established that the smallest digestion fragment was alpha-D-NeupNAc-(2----3)-beta-D-Galp-(1----4)-[beta-D-Glcp-(1----6 )]- beta-D-GlcpNAc-(1----3)-beta-D-Gal. The isolation of this oligosaccharide is consistent with the susceptibility of the beta-D-Galp-(1----4)-beta-D-Glcp linkage in the backbone of the type III group B streptococcal polysaccharide and confirms that the polysaccharide is composed of a pentasaccharide repeating unit. High resolution 13C NMR spectroscopic studies indicated that, as in the case of the pentasaccharide, the terminal sialic acid residues of the type III group B streptococcal polysaccharide were linked to O-3 and not to O-6 of its branch beta-D-galactopyranosyl residues as had been previously reported (Jennings, H. J., Rosell, K.-G., and Kasper, D. L. (1980) Can. J. Chem. 58, 112-120). This linkage was confirmed in an independent methylation analysis of the type III group B streptococcal polysaccharide. Thin layer chromatogram binding assay and radioactive antigen binding assays with radiolabeled oligosaccharides demonstrated the single repeating unit pentasaccharide oligosaccharide to be poorly antigenic. Increasing oligosaccharide size to a decasaccharide consisting of two repeating units resulted in an 8-fold increase in antigen binding in the direct radioactive antigen binding assay. The results suggest that a region of the immunodeterminant site critical for antibody binding is located in the backbone of the polysaccharide and involves the beta-D-galactopyranose-(1----4) beta-D-glucopyranose bond.     

Structural analysis of the surface polysaccharide of Staphylococcus aureus M.

The chemical structure of the surface polysaccharide from Staphylococcus aureus M was investigated by a combination of methanolytic, hydrolytic, and chromatographic techniques. The repeating unit that was most consistent with the data was a hexasaccharide composed of N-acetyl-D-aminogalacturonic acid, N-acetyl-D-fucosamine, and taurine in molar ratios of 4:2:1. A disaccharide was isolated and characterized, by combined gas-liquid chromatography-mass spectrometry, as N-acetyl-D-aminogalacturonyl-(1 leads to 3)-N-acetyl-D-fucosamine. Taurine is linked to a carboxyl group of N-acetyl-D-aminogalacturonic acid via an amide bond.     

Structural profiling of lipopolysaccharide glycoforms expressed by non-typeable Haemophilus influenzae: phenotypic similarities between NTHi strain 162 and the genome strain Rd

Non-typeable Haemophilus influenzae (NTHi) is a significant cause of otitis media in children. We have employed single and multiple step electrospray ionization mass spectrometry (ESIMS) and NMR spectroscopy to profile and elucidate lipopolysaccharide (LPS) structural types expressed by NTHi strain 162, a strain obtained from an epidemiological study in Finland. ESIMS on O-deacylated LPS (LPS-OH) and core oligosaccharide (OS) samples of LPS provided information on the composition and relative abundance of glycoforms differing in the number of hexoses linked to the conserved inner-core element, L-alpha-D-Hepp-(1-->2)-[PEtn-->6]-L-alpha-D-Hepp-(1-->3)-L-alpha-D-Hepp-(1-->5)-[PPEtn-->4]-alpha-Kdop-(2-->6)-Lipid A of H. influenzae LPS. The strain examined was found to elaborate Hex2 to Hex5 LPS glycoform populations having structures identical to those observed for H. influenzae strain Rd [Risberg, A.; Masoud, H.; Martin, A.; Richards, J.C.; Moxon, E.R.; Schweda, E.K.H. Eur. J. Biochem. 1999, 261, 171-180], the strain for which the complete genome has been sequenced. In addition, sialyllactose-containing glycoforms previously identified in strain Rd as well as several NTHi strains, were identified as minor components. Multiple step tandem ESIMS (MS(n)) on dephosphorylated and permethylated OS provided information on the arrangement of glycoses within the major population of glycoforms and on the existence of additional isomeric glycoforms. Minor Hex1 and Hex6 glycoforms were detected and characterized where the Hex6 glycoform was comprised of a dihexosamine-containing pentasaccharide chain attached at the proximal heptose residue of the inner-core unit. LPS structural motifs present in the NTHi strain 162 are expressed by a genetically diverse set of disease causing isolates, providing the basis for a vaccine strategy against NTHi otitis media.     

A new synthesis of 9-(2-deoxy-2-fluoro-beta-D-arabinofuranosyl)guanine (AraF-G)

Interesting and very promising antisense properties of 2'-deoxy-2'-fluoroarabinonucleic acids ((a) Wilds, C.J.; Damha, M.J. 2'-Deoxy-2'-fluoroarabinonucleosides and oligonucleotides (2'F-ANA): synthesis and physicochemical studies. Nucl. Acids Res. 2000, 28, 3625-3635; (b) Viazovkina, E.; Mangos, M.; Elzagheid, M.I.; Damha, M.J. Current Protocols in Nucleic Acid Chemistry 2002, 4.15.1-4.15.21) (2'F-ANA) has encouraged our research group to optimize the synthetic procedures for 2'-deoxy-2'-fluoro-beta-D-arabinonucleosides (araF-N). The synthesis of araF-U, araF-T, araF-A and araF-C is straightforward, (Tann, C.H.; Brodfuehrer, P.R.; Brundidge, S.P.; Sapino, C., Jr. Howell H.G. Fluorocarbohydrates in synthesis. An efficient synthesis of 1-(2-deoxy-2-fluoro-beta-D-arabinofuranosyl)-5-iodouracil (beta-FIAU) and 1-(2-deoxy-2-fluoro-beta-D-arabinofuranosyl)thymine (beta-FMAU). J. Org. Chem. 1985, 50, 3644-3647; Howell, H.G.; Brodfuehrer, P.R.; Brundidge, S.P.; Benigni, D.A.; Sapino, C., Jr. Antiviral nucleosides. A stereospecific, total synthesis of 2'-fluoro-2'-deoxy-beta-D-arabinofuranosyl nucleosides. J. Org. Chem. 1988, 53, 85-88; Maruyama, T.; Takamatsu, S.; Kozai, S.; Satoh, Y.; Izana, K. Synthesis of 9-(2-deoxy-2-fluoro-beta-D-arabinofuranosyl)adenine bearing a selectively removable protecting group. Chem. Pharm. Bull. 1999, 47, 966-970) however, the synthesis of the guanine analogue is more complicated and affords poor to moderate yields of araF-G (4) ((a) Elzagheid, M.I.; Viazovkina, E.; Masad, M.J. Synthesis of protected 2'-deoxy-2'-fluoro-beta-D-arabinonucleosides. Synthesis of 2'-fluoroarabino nucleoside phosphoramidites and their use in the synthesis of 2'F-ANA. Current Protocols in Nucleic Acid Chemistry 2002, 1.7.1-1.7.19; (b) Tennila, T.; Azhayeva, E.; Vepsalainen, J.; Laatikainen, R.; Azhayev, A.; Mikhailopulo, I. Oligonucleotides containing 9-(2-deoxy-2-fluoro-beta-D-arabinofuranosyl)-adenine and -guanine: synthesis, hybridization and antisense properties. Nucleosides, Nucleotides and Nucl. Acids 2000, 19, 1861-1884). Here we describe an efficient synthesis of araF-G (4) that involves coupling of 2-deoxy-2-fluoro-3,5-di-O-benzoyl-alpha-D-arabinofuranosyl bromide (1) with 2-chlorohypoxanthine (2) to afford 2-chloro-beta-araF-I (3) in 52% yield. Nucleoside (3) was transformed into araF-G (4) by treatment with methanolic ammonia (150 degrees C, 6 h) in 67% yield.     

Inactivation of gamma-aminobutyric acid aminotransferase by (Z)-4-amino-2-fluorobut-2-enoic acid

(Z)-4-Amino-2-fluorobut-2-enoic acid (1) is shown to be a mechanism-based inactivator of pig brain gamma-aminobutyric acid aminotransferase. Approximately 750 inactivator molecules are consumed prior to complete enzyme inactivation. Concurrent with enzyme inactivation is the release of 708 +/- 79 fluoride ions; transamination occurs 737 +/- 15 times per inactivation event. Inactivation of [3H]pyridoxal 5'-phosphate ([3H]PLP) reconstituted GABA aminotransferase by 1 followed by denaturation releases [3H]PMP with no radioactivity remaining attached to the protein. A similar experiment carried out with 4-amino-5-fluoropent-2-enoic acid [Silverman, R. B., Invergo, B. J., & Mathew, J. (1986) J. Med. Chem. 29, 1840-1846] as the inactivator produces no [3H]PMP; rather, another radioactive species is released. These results support an inactivation mechanism for 1 that involves normal catalytic isomerization followed by active site nucleophilic attack on the activated Michael acceptor. A general hypothesis for predicting the inactivation mechanism (Michael addition vs enamine addition) of GABA aminotransferase inactivators is proposed.