4-Methylumbelliferyl 5-Acetamido-3,4,5-trideoxy-α-D-manno-2-nonulopyranosidonic Acid: Synthesis and Resistance to Bacterial Sialidases

The synthesis of 4-methylumbelliferyl α-D -glycoside 13 of N-acetyl-4-deoxyneuraminic acid and its behaviour towards bacterial sialidases is described. N-Acetyl-4-deoxyneuraminic acid ( 1 ) was transformed into its methyl ester 2 and then acetylated to give the anomeric pentaacetates 3 and 4 of methyl 4-deoxyneuraminate and the enolacetate 5 (Scheme). A mixture 3/4 was treated with HCl/AcCl to give the glycosyl chloride, which was directly converted into the 4-methylumbelliferyl α-D -glycoside 9 of methyl 7-O,8-O,9-O,N-tetraacetylneuraminate and into the 2,3-dehydrosialic acid 11 . The ketoside 9 was de-O-acetylated to 12 with NaOMe in MeOH. Saponification (NaOH) of the methyl ester 12 followed by acidification gave the free 13 , which was also converted into the sodium salt 14 by passage through Dowex 50 (Na⁺). The 4-deoxy α-D -glycoside 13 is not hydrolyzed at significant rates by Vibrio cholerae and Arthrobacter ureafaciens sialidase. Neither the free N-acetyl-4-deoxyneuraminic acid ( 1 ), nor the α-D -glycoside 13 inhibit the activity of these sialidases.     

Synthesis of Pyrrolidine Analogues of N-Acetylneuraminic Acid as Potential Sialidase Inhibitors

The pyrrolidine derivatives 3 , 4 , and 5 were prepared from the methyl ester 7 of Neu2en5Ac via lie pyrrolidine-borane adduct 33 . They inhibit Vibrio cholerae sialidase competitively with K_i = 4. 4 10^?3 M, 5. 3 10^?3 M, and 4. 0 10^?2 M, respectively. Benzylation of 7 gave the fully O-benzylated 8 besides 9, 10 , and 11. Ozonolysis and reduction with NaBH₄ of 8 and 9 gave the 1, 4-diols 12 and 15 , the hydroxy acetates 13 and 16 , and the furanoses 14 and 17 (Scheme 1), respectively. The diol 12 was selectively protected (→ 19 → 20 → 23 ) and transformed into the azide 27 by a Mitsunobu reaction. Selective base-catalysed deprotection of the diacetate 22 , obtained from 12 , was hampered by an easy acetyl-group migration. The mesylate 28 proved unstable. The azide 27 was transformed via 29 into the ketone 30 (Scheme 2). Hydrogenation of 30 gave the dihydropyrrole 31 and, hence, the pyrrole 32. The adduct 33 was obtained from 30 by a Staudinger reaction (→31) and reduction with LiBH₄/HBF⁴. It was transformed into the pyrroudine 34 . The structure of 34 was established by X-ray analysis. Reductamination of the pyrrolidine-borane adduct with glyoxylic acid gave 40 and, hence, 3. N-Alkylation afforded 44 and, hence, the phosphonate 4. The acid 5 was obtained from 33 by acylation (→ 47 ) and deprotection (Scheme 4).     

N-(4-Nitrophenyl)oxamic Acid and Related N-Acylanilines Are Non-competitive Inhibitors of vibrio cholerae sialidase but do not inhibit trypanosoma cruzi or trypanosoma brucei trans-sialidases

N-(4-Nitrophenyl)oxamic acid 1 , N-(2-fluoro-4-nitrophenyl)oxamic acid 7 , N-(4-nitrophenyl)-trifluoroacetamide 3 , and N-(2-methoxy-4-nitrophenyl)trifluoroacetamide 9 are non-competitive inhibitors of Vibrio cholerae sialidase with K_i-values ranging from 2.66 to 5.18 · 10^?4 M . These compounds, and the N-acetylneuraminic-acid analogues 11–13 do not inhibit the sialidase and trans-sialidase activities from Trypanosoma cruzi; nor does N-(4-nitrophenyl)oxamic acid ( 1 ) inhibit the corresponding enzyme activities from T. brucei.     

2-Deoxy-2,3-dehydro-sialinsäuren, 3. Mitt.: Hemmung derVibrio cholerae-Neuraminidase durch Oxidationsprodukte der 2-Deoxy-2,3-dehydro-N-acetylneuraminsäure

Zusammenfassung 2-Deoxy-2,3-dehydro-N-acetylneuraminsäure-methylester wurde mit Perjodsäure zu 4-Hydroxy-5-acetylamino-6-formyl-2,3-dehydropyran-2-carbonsäure-methylester oxidiert. Nach der Reduktion mit NaBH₄ erhielten wir 4-Hydroxy-5-acetylamino-6-hydroxymethyl-2,3-dehydropyran-2-carbonsäure-methylester.Vibrio cholerae-Neuraminidase wird von 4-Hydroxy-5-acetylamino-6-formyl-2,3-dehydropyran-2-carbonsäure, dereniso-Nicotinoylhydrazon sowie von 4-Hydroxy-5-acetylamino-6-hydroxymethyl-2,3-dehydropyran-2-carbonsäure gehemmt.

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2-Deoxy-2,3-dehydrosialic acids, III: Inhibition of vibrio cholerac neuraminidase by oxidation products of 2-deoxy-2,3-dehydro-N-acetyl-neuraminic acid

Methyl 2-deoxy-2.3-dehydro-N-acetylneuraminate was oxidized with periodic acid to methyl 4-hydroxy-5-acetylamino-6-formyl-2.3-dehydropyran-2-carboxylate. On treatment with carbonyl reagents the aldehyde gave the expected derivatives. Upon reduction with NaBH₄ methyl 4-hydroxy-5-acetylamino-6-hydroxymethyl-2.3-dehydropyran-2-carboxylate was formed.Vibrio cholerae neuraminidase was inhibited by 4-hydroxy-5-acetylamino-6-formyl-2.3-dehydropyran-2-carboxylic acid, by itsiso-nicotinoylhydrazone, and by 4-hydroxy-5-acetylamino-6-hydroxymethyl-2.3-dehydropyran-2-carboxylic acid.

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Mit 3 Abbildungen

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A-1121 Wien, Laskegasse 5-11.     

Specific reactivity of 2,4,6-tri-tert-butylanilide anions and its application to benzylation reagent

The reaction of methyl iodide with an anilide anion prepared from 2,4,6-tri-tert-butylanilide and NaH in CH₃CN gave N-methyl anilide (N-alkylation product) as a major product, while in the reaction of benzyl bromide with the anilide anion in DMF, O-benzyl imidate (O-alkylation product) was obtained with almost complete selectivity. The treatment of O-benzyl imidate with alcohols and carboxylic acids in the presence of trifluoromethane sulfonic acid gave benzyl ethers and benzyl esters, respectively.     

Synthesis of New Sialidase Inhibitors, 6-Amino-6-Deoxysialic Acids

The synthesis of the 6-amino-6-deoxysialic-acid analogues 4, 5 , and 6 , is described. Mitsunobu reaction of the 1-C-nitroglycal 8 , (PPh₃, HCOOH, DEAD) gave the formiate 10 with inversion of configuration at C(3) (Scheme 2). Treatment of 10 with aq. NH₃ and subsequent protection of the amino function gave the imines 14 and 15 (Scheme 3), which were transformed into the triflates 17 . Substitution by azide, deprotection, and N-acetylation gave the anormeric 2-acetamido-3-azido-1-deoxy-1-nitro-D -mannoses 16 and the enol ether 18 . Chain elongation of the nitro azides 16 followed by hydroylsis gave the nonulosonates 20/22 , which upon reduction yielded the diols 23 and 24 , respectively (Scheme 4). The diol 23 was transformed into the sialic-acid analogues 5, 6 , and 32 by ozonolysis, transfer hydrogenation, hydorgenolysis, and deprotection (Scheme 5), and the diol 24 into 4 by a similar reaction sequence. The sialic-acid analogues 4 and 6 inhibit bacterial and viral sialidases competitively. The inbibitor constants for this enzyme from Vibrio cholerae are 0.12 mm for 4 and 0.19 mm for 6 , respectively. The activity of fowl plague virus sialidase was reduced by 17% and 36% under the influence of 4 and 6 , respectively, at a concentration of 0.1 mM . Compound 5 was inactive.     

Phase-transfer catalysis in the N-benzylation of adenine

A convenient phase-transfer catalysis in the N-benzylation of adenine is described. The benzylation of adenine with benzyl halides in a two-phase system containing phase-transfer catalyst gave 9-benzylated adenines as a major product accompanied with 3-benzylated adenines.     

Synthesis and Biological Properties of N-Acetyl-4-deoxy-D-neuraminic Acid

N-Acetylneuraminic acid ( 1 ) can be transformed into the methyl α-D -ketoside 2 which, by reaction with methanesulfonyl chloride, yields the corresponding 4-O-mesylate 3 and the 4,7-di-O-mesylate 4 as a by-product. Compound 3 reacts with Nal giving the 4-deoxy-4-iodo compound 5 with equatorial orientation of the I-atom. As second product, the dihydrooxazole 6 is produced. Catalytic hydrogenation of 5 is followed by ester cleavage and removal of the isopropylidene group yielding the methyl α-D -ketoside 8 which affords the title compound, N-acetyl-4-deoxyneuraminic acid ( 9 ), by reaction with fowl plague virus sialidase. Further biochemical activities of 8 and 9 are reported.     

Reaction Pathways upon Interaction of Allenic Phosphonates with Selenyl Chlorides

Abstract

Studies were performed on the reaction between alkyl- and arylselenyl chlorides with esters of allenic phosphonic acids, variously substituted at their terminal C-atom. With the esters of the C-3 diasubstituted acids the reaction is highly regioselective and only oxaphosphol heterocyclization occurs to 2,5-dihydro-1,2-oxaphosphols 21-e. With the esters of the propadiene phosphonic acid the reaction is regio- and (Z)-stereoselective: only the 2,3-adducts 3a-b are formed, where the (Z)-isomer and the allenic phosphonates 4a-b are prevalent, as a result of 1,3-sigmatropic isomerization of 3a-b. With the esters of the C-3 monosubstituted acids, complex reaction mixtures are formed. From them were isolated: (E)- and (Z)-isomers of 2,5-dihydro-1,2-oxaphosphols 2f-j; (E)-and (Z)-isomers of the 2,3-adducts 3c-h; (E)-and (Z)-isomers of 4c-f; and (E)-and (Z)-isomers of the 1,2-adducts 5a-d. The reaction partially loses its regioselectivity, but the (Z)-stereoselectivity is preserved:     

Analogues of Sialic Acids as Potential Sialidase Inhibitors Synthesis of 2-C-Hydroxymethyl Derivatives of N-Acetyl-6-amino-2,6-dideoxy-neuraminic Acid

The intramolecular cycloaddition of the previously described azidoalkene 16 , the related diacetates 7 and 13 , and the monoacetate 8 led diastereoselectivity to the (2R)- and (2S)-configurated hydropyridotriazoles 17 , 9 and 11 , 14 and 15 , and 10 and 12 , respectively (Scheme 1). Thermolysis of 16 gave also the aziridine 18 , its proportion increasing with reaction time. The diastereoselectivity of the cycloaddition- is rationalized on the basis of steric interactions and of H? bonds in the transition state. Photolysis in benzene partially transformed 9 into the aziridine 19 . Treatment of 9 with aqueous AcOH gave 19 and the tetrahydrofuran 20 , with AcOH in benzene 20 and the triacetate 23 , and with aqueous H₂SO₄ in THF, the primary alcohol 22 (room temperature) or 19 and 22 (0°). Deacetylation of 9 followed by reaction with pyridinium hydrochloride led to the tetrahydrofuran 21 and the chloride 24 (Scheme 2). The diacetate 22 and the triacetate 23 gave the tripl 25 which was deprotected to 26 . Reduction of the keto-aziridine 18 (NaBH₄) gave the alcohols 27 and 29 which were acetylated to give 28 and 19 , respectively (Scheme 3). Treatment of the aziridine 28 with AcOH in benzene followed by deacetylation gave 30 and hence 31 . AcOH in benzene transformed the triazoline 15 first into the aziridine 32 and hence into 33 , which was deprotected to give the triol 34 and hence 35 . The 2-(hydroxymethyl)piperidines 26 , 31 , and 35 inhibited Vibrio cholerae sialidase with K₁ = 3.8 · 10^?2 M, 3.4 · 10^?3 M, and 1.5 · 10^?4 M, respectively. The conformation of the glycerol side chain of these compounds and of the unbranched piperidines 2–4 deviates from the one of Neu5Ac (and Neu2en5Ac). This finding is rationalized by an H-bond between OH? C(8) and NH? C(6). The conformations and the K₁ values of 26 , 31 , and 35 correlate with each other.     

Enzymatic Hydrolysis of N-Acylated 1-Aminophosphonic Acids

Abstract

Penicillin acylase from E. coli (FC 3.5.1.11) was found to hydrolyse N-phenylacetylated 1-aminoalkylphosphonic acids and their esters. Enzyme preferentially converts the R-form of the substrates: the ratios of the bimolecular rate constants of penicillin acylase-catalysed hydrolysis of R-and S- forms of 1-(N-phenylacetaminol-ethylphosphonic acid and its dimethyl- and diisopropyl- esters are 58000, 2600, 1800; these derivatives were shown to have the greatest values of the catalytic constants for enzymatic hydrolysis of all known substrates of penicillin acylase: 237, 148, and 134 s; corresponding values of Michaelis constants are 3.7×10^?5, 6.8×10^?4, and 6.2×10^?4 M. The kinetics of the enzymatic hydrolysis of 1-(N-phenylacetaminol-ethylphosphonic acid was investigated up to high degrees of conversion. The inhibition of penicillin acylase by high concentrations of the R-form of the substrate (with substrate inhibition constant 0.07 Ml and competitive inhibition by the reaction product phenylacetic acid (K_i=3.5×10_?5 M) was observed. Penicillin acylase was shown to possess quite broad substrate specificity among N-acylated 1-aminoalkylphosphonic acids and was found to be capable of hydrolysing 1-(N-phenylacetaminol-substituted 2-phenylethyl-, 1-phenylmethyl- and 3-methylbutylphosphonic acids with high efficiency and enantioselectivity.     

17O NMR spectroscopy: Effect of substituents on chemical shifts for p-substituted benzoic acids,methyl benzoates,cinnamic acids and methyl cinnamates

The ¹⁷O NMR spectra for a series of ¹⁷O-enriched p-substituted benzoic acids, methyl benzoates, cinnamic acids and methyl cinnamates in acetone at 40°C are reported. The carboxylic acids showed one signal (benzoic 250.5 ppm, SCS range p-MeO to p-NO₂ = 10.5 ppm; cinnamic 254.1 ppm, SCS range p-MeO to p-NO₂ = 5.4 ppm). The esters showed two signals [methyl benzoate (C?O) 341.3 ppm and (OCH₃) 128.0 ppm; methyl cinnamate (C?O) 339.9 ppm and (OCH₃) 134.2 ppm]. The SCS ranges for the carbonyls of the esters were larger than those for the corresponding acids, while those for the OCH₃ groups of the esters were slightly smaller. The carbonyl data gave good correlations with σ⁺ constants, while the OCH₃ data gave at best only a poor correlation with σ constants. Dual substituent parameter treatment improved the correlations for all the data using σ_R+ constants. The ratios of ρ_I to ρ_R+ were similar for all the sets of data.     

Deoxy-nitrosugars. 16th Communication. Synthesis of N-acetyl-4-deoxyneuraminic acid

The synthesis of 5-acetamido-4-deoxyneuraminic acid ( 1 ) is described. Acetylation of a mixture of the epimeric triols 4 and 5 gave the tetraacetates 7 and 8 (Scheme 1). Ozonolysis of a mixture of these acetates followed by base-promoted β-elimination led to the (E) -configurated α,β-unsaturated keto ester 10 , which was hydrogenated to give the saturated keto ester 11 . Saponification of 11 and hydrolytic removal of the benzylidene group followed by anion-exchange chromatography gave the 5-acetamido-4-deoxyneuraminic acid ( 1 , Scheme 1 and 2). De-O-acetylation (NaOMe/MeOH) of the keto ester 11 gave a mixture of the tert-butyl ester 12 and the methyl ester 13 , which were converted to tert-butyl N-acetyl-4-deoxyneuraminate ( 14 ) and to methyl N-acetyl-4-deoxyneuraminate ( 15 ), respectively. Hydrogenolysis of the benzylidene acetal 11 followed by de-O-acetylation gave the pentahydroxy ester 16 .     

N-Monoalkylation of Tetra-O-benzyl-D-arabinonamide: Synthesis of Some Open-Chain Analogues of N-Acetylneuraminic Acid and Their Evaluation as Sialidase Inhibitors

N-Arabinonoylglycine 2 , its phospho analogue (arabinonoylamino)methylphosphonate 14 , N-arabinonoyltaurine salt 18 , and [2-(arabinonoylamino)ethylidene]bis[phosphonic acid] 22 have been synthesized from D -arabinose in seven ( 2 or 14 ), and eight steps ( 18 or 22a ), respectively. With the exception of the salt 22b , none of these compounds showed a significant inhibitory activity in vitro against the sialidases of Vibrio cholerae, Salmonella typhimurium, or Influenza A (N9), or B (B/Lee/40) virus. Ammonolysis of the oxosulfonate 8 obtained by oxidation of the hydrogensulfite adduct 7 of 2,3,4,5-tetra-O-benzyl-aldehydo-D -arabinose ( 6 ) yielded the primary amide 9 (64% from 6 ), which was alkylated with the triflates 10 or 11 of benzyl glycolate and dibenzyl hydroxymethylphosphonate, respectively, to give the protected N-arabinonoylglycinate 12 and the (arabinonoylamino)methylphosphonate 13 (45 and 90%, resp.). N-Alkylation of 9 with 2-bromoethyl triflate 15 followed by nucleophilic displacement with sodium sulfite yielded the protected taurine analogue 17 (21% from 9 ), whereas the protected tetraethyl bis[phosphonate] 20 was formed in 90% yield by 1,4-addition of 9 to tetraethyl ethenylidenebis[phosphonate] 19 . Debenzylation of 12 and 13 , followed by purification by reversed-phase HPLC gave the triethylammonium salt of N-(D -arabinonoyl)glycine ( 2 ) and triethylammonium (D -arabinonoylamino)methylphosphonate ( 14 b ), respectively, whereas the deprotection of 17 afforded the N-(D -arabinonoyl)taurine salt 18 . Debenzylation of 20 , followed by treatment with Me₃SiBr and hydrolysis of the resulting silyl ester gave the bis[phosphonic acid] 22 a (3 steps, 88%).     

Simple synthesis of mixed cellulose acylate phosphonates applying n-propyl phosphonic acid anhydride

Cellulose mixed esters containing alkylphosphonate and carboxylate groups were prepared homogeneously by a new one-pot method using n-propyl phosphonic acid anhydride (T3P^?) in LiCl/N-methyl-2-pyrrolidone (NMP). n-Propyl phosphonic acid anhydride acts as both an activating agent for carboxylic acids and phosphonation reagent. Cellulose mixed esters with DS_acyl ranging from 1.4 to 1.8, and DS_phos up to 0.7 could be prepared. The structure of the cellulose mixed esters was elucidated by FTIR- and NMR spectroscopy, as well as by GPC and solubility tests.     

Synthesis and Enzyme-Inhibition Studies of Phenylsemicarbazones derived from D-glucono-1,5-lactone and 2-acetamido-2-deoxy-D-glucono-1,5-lactone

The carbohydrate-derived lactone phenylsemicarbazones 3 and 4 were prepared from 5 and 8 (Scheme). Treatment with 4-phenylsemicarbazide gave 6 and 7 (77:23) and 9 and 19 (76:24), respectively. Oxidation of 6 and 9 by CrO₃–pyridine to 11 and 13 , followed by deprotection, yeilded 3 and 4 . The structure of 3 was established by X-ray analysis. Enzyme-inhibition studies using revealed that 3 is a competitive inhibitor with K_i = 23 μm. The activity of 4 was examined using N-acetylglucosaminidase from bovine kidney, Aspergillus niger, and Artemia salina. compound 4 was found to be a competitive inhibitor of all three enzymes with K_i values of 0.13, 6.0, and 0.71 μm and K_M/K_i values of 6910, 45, and 465, respectively.     

Stereoregularity of poly(alkyl α-chloroacrylates) and mechanism of isotactic polymerization

The catalytic activity of the complexes prepared by the reaction of Grignard reagents with ketones, esters, and an epoxide as polymerization catalysts of methyl and ethyl α-chloroacrylates was investigated. The modifiers which gave isotactic polymers were α,β-unsaturated ketones such as benzalacetophenone, benzalacetone, dibenzalacetone, mesityl oxide, and methyl vinyl ketone, and α,β-unsaturated esters such as ethyl cinnamate, ethyl crotonate, and methyl acrylate. Catalysts with butyl ethyl ketone, propiophenone, and propylene oxide as modifiers produced atactic polymers but no isotactic polymers. It was revealed that the complex catalysts having a structure ? C?C? O? MgX (X is halogen) gave isotactic polymers. The mechanism of isotactic polymerization was discussed. In addition, for radical polymerization of ethyl α-chloroacrylate, enthalpy and entropy differences between isotactic and syndiotactic additions were calculated to give ΔH_i^* ? ΔH_s^* = 910 cal/mole and ΔS_i^* ? ΔS_s^* = 0.82 eu.     

Gas chromatographic enantiomer separation with modified cyclodextrins: Carboxylic acid esters and epoxides

The wide range of application of 2,6-di-O-methyl-3-O-pentyl-β-and y-cyclodextrins is demonstrated by the resolution of the enantiomers of the methyl esters of chiral carboxylic acids: α and β hydroxy acids with up to 18 carbon atoms, hydroxy di- and tricarboxylic acids, and alkyl/aryl-substituted carboxylic acid methyl esters, including the plant hormone abscisic acid, insect juvenile hormones, and some non-steroidal anti-inflammatory drugs can be resolved with generally large separation factors. The new cyclodextrin derivatives also exhibit high selectivity for epoxides.     

Separation of Enantiomers of N-Protected Non-Protein Amino Acid Esters by Chiral High-Performance Liquid Chromatography

The high-performance liquid chromatographic separation of enantiomers of N-protected non-protein amino acid esters was investigated by using a cellulose tris(3,5-dimethylphenylcarbamate) chiral stationary phase column (Daicel Chiracel OD). The effect of the N-protecting groups and the ester groups on chiral discrimination was examined. The benzyloxycarbonyl (Z), 4-methoxybenzyloxycarbonyl, and 9-fluorenylmethoxycarbonyl derivatives gave good enantiomeric separations, while the formyl and t-butoxycarbonyl groups marred them. Almost all the alkyl esters examined and the benzyl ester gave enantiomeric separations better than or of the same order as the methyl ester. The N-Z-protected methyl esters of a number of non-protein -amino acids were well resolved using hexane–2-propanol as a mobile phase. The resolution of -amino acid derivatives was inferior to that of the isomeric -amino acid derivatives.     

Synthesis of Novel New 2-(2-(4-((3,4-Dihydro-4-oxo-3-aryl quinazolin-2-yl)methyl)piperazin-1-yl)acetoyloxy)-2-phenyl Acetic Acid Esters

Stereoselective diazotization of (S)-2-amino-2-phenyl acetic acid (L-phenyl glycine) (4) with NaNO₂ in 6% H₂SO₄ in a mixture of acetone and water gave optically pure (S)-2-hydroxy-2-phenyl acetic acid (L-mandelic acid) (5). Esterification, gave (S)-2-hydroxy-2-phenyl acetic acid esters (6). The latter was treated with chloroacetyl chloride in the presence of triethylamine (TEA) in dichloromethane (DCM) to yield (S)-2-chloroacetyloxy phenyl acetic acid ester (2). In another sequence, the reaction of 2-(chloromethyl)-3-arylquinazolin-4(3H)-one (9) treated with N-Boc piperazine, followed by deprotection of the Boc group, to obtain 3-aryl-2-((piperazin-1-yl)methyl) quinazolin-4(3H)-one (3). Reaction of 2 with 3 in the presence of K₂CO₃ and KI gave the title compound, 2-(2-(4-((3,4-dihydro-4-oxo-3-arylquinazolin-2-yl)methyl)piperazin-1-yl) acetoyloxy)-2-phenyl acetic acid esters (1). The structures of all the new compounds obtained in the present work are supported by spectral and analytical data.