Search

2,2′-Anhydro-1-(5,6-di-O-benzoyl-β-D-altrofuranosyl)thymine 6 and uracil derivative 7 are prepared by transformation of the corresponding 5′,6′-di-O-benzoyl-3′-O-mesyl-β-D-glucofuranosyl nucleosides 4 and 5 into the 2,2′-anhydro derivatives 6 and 7 using DBU.

1-(3′-Fluoro-2′,3′,6′-trideoxy-β-D-allofuranosyl)thymine [7] and 1-(3′-fluoro-2′,3′,6′-trideoxy-α-L-talofuranosyl) thymine [8] were synthesized starting from the corresponding 2,3′-anhydro nucleoside derivatives. The fluorine was introduced stereoselectively by opening of the anhydro bridge in the presence of HF/AIF3. The 5′-C-methyl derivatives, [7] and [8], of 3′-fluoro-3′-deoxythymidine (FLT) were evaluated for their inhibitory effect against human immunodeficiency virus type 1 (HIV-1) and type 2 (HIV-2). The compounds [7] and [8] had antiviral activity which was three orders of magnitude lower than the reference compound 3′-fluoro-3′-deoxythymidine. None of the compounds showed appreciable activity against other RNA or DNA viruses at subtoxic concentrations.

Methyl 5- acetamido-7,8,9-tri -O- acetyl-4-azido-2,3-didehydro-2,3,4,5-tetradeoxy- d -glycero- d -talo- nonulopyranosonate with N-bromosuccinimide in methanol gave methyl (methyl 5- acetamido-7,8,9-tri -O- acetyl-4-azido-3-bromo-3,4,5-trideoxy-α- d -glycero- d -talo- nonulopyranosid)onate and methyl (methyl 5- acetamido-7,8,9-tri -O- acetyl-4-azido-3-bromo-3,4,5-trideoxy-β- d -glycero- d -talo- nonulopyranosid)onate , which on reductive acetylation with H 2 PdC in acetic anhydride-ethyl acetate yielded the corresponding 4-acetamido analogues. Debromination with Bu 3 SnH AIBN in toluene, followed by hydrolysis, gave methyl 4-acetamido-N-acetyl-4-deoxy-α-and β-4-epi-neuraminic acids.

We have continued our work to develop novel analogues of sialic acid [1–4] that may specifically modulate the interaction between endogenous sialic acid and influenza virus haemagglutinin [3,5,6]. Functional groups of sialic acid that have been implicated for this virus-host recongnition are the glycerol side chain, N -acetyl group and the axially oriented carboxylic acid function In this report we describe the synthesis of two analogues, namely, 4-epi-2-deoxy-2-H eq - N -acetylneuraminic acid (4-epi-2-d-2-H eq -Neu5Ac) and 2,4-dideoxy-2-H eq - N -acetylneuraminic acid (2,4-d 2 -2-H eq -Neu5Ac).

A Convenient Route to D-Apio-β-D-furanosyl- and 2′-Deoxyapio-β-D-furanosyl Nucleosides 2,3-O-Isopropylidene-D-apio-β-D-furanose (1), available in 40% overall yield by modified literature procedures, is acylated regioselectively to the new 3′-O-benzoyl-derivative 2. This is converted to the anomeric triacetates 4 (β-4; α-4 = 1.8:1) by cleavage of the isopropylidene protecting group from 2 followed by peracetylation. Reaction of compounds 4 with silylated nucleobases and subsequent deprotection gives the D-apio-β-D-furanosyl nucleosides 8–10 in good yields. Regioselective hydrazinolysis of the protected nucleosides 5 and 6 affords the 2′-hydroxy-derivatives 11 and 12, respectively, which are converted to the 2′-deoxyapio-β-D-furanosyl nucleosides 17 and 18, respectively, via deoxygenation of the corresponding thionocarbonates 13 and 14 with tris(trimethylsilyl)silane and subsequent deprotection. The 2′-deoxyapio-β-D-furanosyl cytosine 20 is prepared from the 2′-deoxyapio-β-D-furanosyl uracil derivative 16.

A Convenient Route to 3′-Deoxy-α-L- and 3′-Deoxy-β-D-apionucleosides The cyclic thionocarbonate 3, easily available in three steps from 3′-O-benzoyl-2,3-O-isopropylidene-D-apio-β-D-furanose (1), is deoxygenated with n-Bu3SnH to yield the 3′-deoxy epimers 4 [methyl 3-C-(benzoyloxymethyl)-3-deoxy-α-L-threo-tetrofuranoside] and 6 [methyl 3-C-(benzoyloxymethyl)-3-deoxy-β-D-erythro-tetrofuranoside]. These are separated by chromatography and further converted to the 3′-deoxy-α-L-apionucleosides 11–13, and the 3′-deoxy-β-D-apionucleosides 17–19, respectively.

Efficient stereospecific N-formylation of ribosylamine has been achieved, affording the α-anomer directly (by reaction with formic-acetic anhydride) and the β-anomer via the corresponding formamidine derivative (by reaction with dimethylformamide dimethyl acetal). Dehydration of the α-anomer gave the corresponding isocyanide without compromising the anomeric purity. The amidine route was extended to give the N-formyl derivatives of α-xylosylamine and α-arabinosylamine.

The key step in the preparation of 6-deoxy-1,2-O-isopropylidene-β-L-talofuranose (7) and 6-deoxy-1,2-O-isopropylidene-β-L-idofuranose (13) is the selective exchange of the 6-O-mesyl rest of 3-O-acetyl-5,6-O-dimesyl-1,2-O-isopropylidene-α-D-allofuranose (4) and 3-O-acetyl-5,6-O-dimesyl-1,2-O-isopropylidene-α-D-glucofuranose (10) by acetate group (potassium acetate/18-crown-6).

1-(3′-Azido-2′,3′,5′-trideoxy-β-D-allofuranosyl)thymine 12 (homo-AZT) was synthesized starting from 1,2;5,6-di-O-isopropylidene- 3-O-mesyl-α-D-allofuranose 1 in an eleven step sequence (overall yield: 4%).

Methyl 5- acetamido-7,8,9-tri -O- acetyl-4-azido-2,3-didehydro-2,3,4,5-tetradeoxy- d -glycero- d -talo- nonulopyranosonate with N-bromosuccinimide in methanol gave methyl (methyl 5- acetamido-7,8,9-tri -O- acetyl-4-azido-3-bromo-3,4,5-trideoxy-α- d -glycero- d -talo- nonulopyranosid)onate and methyl (methyl 5- acetamido-7,8,9-tri -O- acetyl-4-azido-3-bromo-3,4,5-trideoxy-β- d -glycero- d -talo- nonulopyranosid)onate , which on reductive acetylation with H 2 PdC in acetic anhydride-ethyl acetate yielded the corresponding 4-acetamido analogues. Debromination with Bu 3 SnH AIBN in toluene, followed by hydrolysis, gave methyl 4-acetamido-N-acetyl-4-deoxy-α-and β-4-epi-neuraminic acids.

2,2′-Anhydro-1-(5,6-di-O-benzoyl-β-D-altrofuranosyl)thymine 6 and uracil derivative 7 are prepared by transformation of the corresponding 5′,6′-di-O-benzoyl-3′-O-mesyl-β-D-glucofuranosyl nucleosides 4 and 5 into the 2,2′-anhydro derivatives 6 and 7 using DBU.

A series of neuraminic acid derivatives modified in the side chain or at C-3, C-4 or C-5 were tested as substrates of inhibitors of N-acetylneuraminate lyase (EC 4.1.3.3) from Clostridium perfringens. The results, together with Km and Ki values reported previously, indicate that the region most important for the binding of sialic acids is an equatorial zone reaching from C-8 via the ring oxygen atom to C-4 of the sugar molecule, whereas the substituents at C-9 and C-5 may be varied to a higher extent without significantly disturbing enzyme action. It is shown that stereo-electronic factors are responsible for the immediate heterolytic fragmentation of the cyclic sialic acid into pyruvic acid and 2-acetamidomannose or a related C-6 sugar.

The α-methylketoside of N-acetylneuraminic acid methylester (4) is transformed via the deacetylated compound5 into the 9,8-O-isopropylidenderivative6 which could be oxidized regioselectively by RuO4 to the corresponding 4-oxo-sialic acid analogue7. Reduction with the boraneammonia complex produces a 1:1 mixture of6 and the desired α-methylketoside of 9,8-O-isopropyliden-4-epi-N-acetyl-neuraminic acid methylester (8). Removing of the isopropylidene group gives the α-methylketoside of 4-epi-N-acetylneuraminic acid methylester (9), which was further transformed to the ammonium salt of 4-epi-N-acetylneuraminic acid α-methylketoside (10). On the other hand compound5 was turned into the 4,8,9-tri-O-t-butyldimethylsilylderivative11 a from which the corresponding 7-oxo-compound12 by oxidation with RuO4 derives. The reduction of12 with BH3 - NH3 yielded a 1:1 mixture of the starting material11 a and the desired 7-epi-derivative13 a which gives either via the purified peracetylated α-methylketosid of 7-epi-N-acetylneuraminic acid methylester (14) or a direct saponification the sodium salt of 7-epi-N-acetylneuraminic acid-α-methylketoside (15).

The synthesis of the sodium 5-acetamido-2,3,5-trideoxy-2,3 didehydro-D-galacto-2,8-nondiulopyranosidonate 8,8-dimethyl acetal (8) and of the methyl-5-acetamido-3,5-dideoxy-α-D-galacto-2,8-nondiulopyranosidonate 8,8 dimethyl acetal (11) as well as of the methyl-5-acetamido-3,5-dideoxy-α-D-galacto-2,8-nondiulopyranosidonic acid (12) is reported involving the easily accessible 8-oxoderivative5. Compounds11 and12, respectively, showed to have glycosidic bond with remarkable stability to acidic conditions.

2-Deoxy-2-Heq-N-acetylneuraminic acid (1a) has been shown to be a versatile mimic for sialosyl 2-α-glycosides to study the hemagglutinin-sialic acid interaction. Starting with a 4-oxo derivative of 2-deoxy-2-Heq-sialic acid, we obtained the 4-C-methylax and 4-C-methyleq derivatives 4 and 5 as a separable mixture. The derivative 4 was formed as a single product by using tributoxymethylzirconium. The 4-C-methylene derivative 10 was formed by treatment of the ketone with Cp2ZrCl2/Zn/CH2I2. Catalytic hydrogenation of the exo-methylene compound 10 yielded the two 4-deoxy-4-C-methyl diastereomers 13 and 14. All above-mentioned derivatives could be transformed into the unprotected 4-branched 2-deoxy-2-Heq-sialic acids 7, 9, 12, 16, and 18. 2-Deoxy-2Heq-4-oxosialic acid (21) was synthesized by a different pathway.

The 5'-azidonucleosides 3 and 4 were obtained by treating thymidine and 2'-deoxyuridine with TPP/DEAD/HN3. The 3'-O-silylated 5'-azido-5'-deoxythymidine 5 and the corresponding 2'-deoxyuridine derivative 6 were transformed to the formamides (7 and 8, respectively) and dehydrated to the protected 5'-isocyano derivatives 9 and 10; deblocking gave 5'-isocyano-5'-deoxythymidine (11) and 5'-isocyano-2',5'-dideoxyuridine (12). 2,3'-Anhydro-5'-formamido derivatives of thymidine and 2'-deoxyuridine (19 and 20, respectively) were prepared by three different ways. In the most direct synthesis 3 and 4 were transformed to the 2,3'-anhydro-5'- azidonucleosides 17 and 18 by using TPP/DEAD; following the reaction with TPP/HCO2COCH3 gave 19 and 20. Nucleophilic opening reaction with LiN3 yielded the 3'-azido-5'-formylamino derivatives 21 and 22. Dehydration to 3'-azido-5'-isocyano-3',5'-dideoxythymidine (23) and 3'-azido-5'-isocyano-2',3',5'-trideoxyuridine (24) was achieved with tosyl chloride/pyridine. In contrast with 3'-azido-3'-deoxythymidine, compounds 11, 12, 23, and 24 were devoid of any marked inhibitory effect against DNA and RNA viruses including human immunodeficiency virus type I (HIV).

Reaction of Dialkyl Phosphites with α-Enones, II. – 2:1 Adducts from Dimethyl Phosphite and α-Enones: Synthesis of (1-Hydroxy-1,3-alkanediyl)diphosphonates and 5-Dimethoxyphosphoryl-2-methoxy-1,2-oxaphospholane P-Oxides On NaOCH3-catalyzed reaction with two equivalents of dimethyl phosphite (2), various α-enones 1 are transformed into the diphosphonates 5 (e.g. 5a, 5b, 5e, 5f), which, depending on the structure of the enone, can further react with ring closure to give the 1,2-oxaphospholanes 6 (e.g. 6c, 6g, 6h), or with phosphonate-phosphate rearrangement of the α-hydroxyphosphonate moiety to yield compounds 7 (e.g. 7d). The formation of the 2:1 adducts is believed to occur via addition of 2 to the carbonyl group of the (3-oxoalkyl)phosphonates 4, formed from thermodynamically controlled 1,4 addition of 2 to 1. Compounds 4 could also be treated with 2 to yield 2:1 adducts (e.g. 4c 5c, 4d 5d, 4d 7d).

The peracetylated methyl ester 1 of N-acetylneuraminic acid was transformed into the oxazoline derivative 2, which was hydrogenated with Pd/C/H2 to give the 4-deoxy-Neu5Ac2en derivative 3. Acid cleavage of the oxazoline 2 by trifluoroacetic acid (THF) gave the 4-epi-Neu5Ac2en derivative 4a, which was saponified to the known 4-epi-Neu5Ac2en 4b. Treatment of 4a with triphenylphosphane/diethylazodicarboxylate (DEAD)/HN3 in toluene gave the 4-azido-4-deoxy-Neu5Ac2en derivative 5a as well as the 4-epi-azido-4-deoxy-Neu5Ac2en derivative 6a. Both epimers could be saponified yielding the free dehydrosialic acid derivatives 5b and 6b. Furthermore, 4-formamido-4-deoxy-Neu5Ac2en 7b was prepared via the derivative 7a, which was formed from 5a by reaction with triphenylphosphane/formyl acetate. In addition, the free dehydrosialic acid derivatives 5b and 6b were transformed into the stable PN ylides 8 and 10, but only 8 could be hydrolyzed to the triethylammonium salt of 4-amino-4-deoxy-Neu5Ac2en 9a, which was converted into the zwitter ionic compound 9b. Finally 4-acetamido-4-deoxy-Neu5Ac2en 11e was prepared from 4-acetamido-4-deoxy-N-acetylneuraminic acid 10 via the derivatives 11a and 11b by well-known methods. The compounds 4b, 5b, 6b, 7b, 9b, and 11c were investigated as inhibitors of Vibrio cholerae sialidase, and their Ki values were determined.

The [heteroaryl(hydroxy)methyl]phosphonates 2-5 (indolizines 2, imidazo[1,2-a]pyridines 3, imidazo[1,2-a]pyrimidines 4, and 2-phenylthiazoles 5, are converted readily to the corresponding O,O-thiocarbonates 6-8 and 18 on treatment with p-tolyloxythiocarbonyl chloride in acetonitrile/4-dimethylaminopyridine, while reaction in pyridine/dichloromethane affords the isomeric O,S-thiocarbonates 9-11 and 19, respectively. Homolytic cleavage of both series of compounds proceeds smoothly, using tributyltin hydride/azobisisobutyronitrile (AIBN) in warm toluene to give the new heteroarylmethylphosphonates 12-14 and 20. Conversion of the O,S-thiocarbonates 9-11 and 19 into the synthetically attractive α-methylthio-substituted derivatives 15-17 and 21 is effected efficiently upon saponification with sodium methoxide in methanol and subsequeng alkylation with methyl iodide

Reaction of Dialkyl Phosphites with α-Enones, I. – Synthesis and Allylic Rearrangement of Dimethyl (1-Hydroxy-2-alkenyl)- and (1-Hydroxy-2-cycloalkenyl)phosphonates Various β,γ-unsaturated α-hydroxyphosphonates 3 are prepared in good yields by NaOCH3-catalyzed regioselective 1,2-addition of dimethyl phosphite to acyclic and cyclic α-enones at −35°C. On acid-catalyzed acetylation, the allylic α-hydroxyphosphonates 3 (R1, R2 + H) rearrange under thermodynamic control; yielding the new 3-acetyloxy-1-(cyclo)alkenyl derivatives 8, from which the transposed allylic alcohols 11 are readily obtained. Using shorter reaction times, acetylation of compounds 3 affords mixtures of 1- and 3-acetylated products, 10 and 8, respectively.

While the reaction of the 4-oxo-Neu 5 Ac derivative2 a with tributoxy methyl zirconate led exclusively to equatorial 4-C-methyl derivative3 a, the analogous reaction with tetramethyl zirconate yielded a 3:2 mixture of both diastereoisomeres3 a and4 a. After removal of protecting groups the 5-acetamido-3,4-dideoxy-4-C-methyl-D-glycero-D-galacto-2-nonulosonic acid5 a and 5-acetamido-3,4-dideoxy-4-C-methyl-D-glycero-D-talo-2-nonulosonic acid6 a were obtained. The 4-C-methylene derivative was prepared by treatment of the same 4-oxo-derivative with CH2I2/Zn/Cp 2ZrCl2. Subsequent hydrogenation led to both epimeric 4-deoxy-4-C-methyl derivatives8 a and9 a. Final removal of protecting groups gave the 5-acetamido-3,4,5-trideoxy-4-C-methyl-D-glycero-D-galacto-2-nonulosonic acid10 a respectively the 5-acetamido-2,7-anhydro-4-C-methyl-3,4,5-trideoxy-D-glycero-D-talo-2-nonulosonic acid11 a. The β-methylketosides of the 4-deoxy-4-C-methyl- (16) and 4-C-methylene-Neu 5 Ac (15) were prepared via the peracetylated derivatives to obtain modell substrates for enzymatic studies. Thus all free acids were tested for inhibition of CMP-sialate synthease. Only the 4-C-methylene compound15 showed most unexpectedly a strong competitive inhibition of this enzyme.

Regioselective 1,2-addition of dimethyl phosphite, diethyl (lithiomethyl)phosphonate, or (lithiomethyl)diphenylphosphine oxide to 2-cyclopenten-1-one (1a) or 2-cyclohexen-1-one (1b) affords the corresponding phosphorus containing, tertiary allylic alcohols 2-4. These, upon oxidation with chromium trioxide reagents are rearranged to the new dialkyl (3-oxo-1-cycloalkenyl)phosphonates, -methylphosphonates or [(3-oxo-1-cycloalkenyl)phosphonates, -methylphosphonates or [(3-oxo-1-cycloalkenyl)methyl]diphenylphosphine oxides 5-7, which are easily transformed to the corresponding epoxy derivatives 8-10

Structural Variations on N-Acetylneuraminic Acid. 22 On the Reaction of Methyl[5-Acetamido-7,8-anhydro-4-O-t-butyldimethylsilyl-3, 5-dideoxy-D-glycero-and-L-glycero-β-galacto-2-nonulopyranosid]onate with Diimidazolylthiocarbonate The title compounds 1 and 3 are transformed with diimidazolylthiocarbonate into the cyclic 8(S),9(O)-dithiocarbonatosialic acid derivatives 2 and 4 as well as into a mixture of the cyclic 8(S),9(O)-monothiocarbonato derivatives 5a and 5b, which turned with acetanhydride pyridine to the corresponding 4-O-t-butyldimethylsilyl-7-O-acetyl- and 4,7-di-O-acetyl derivatives 5c and 5d.

The stereochemistries and the conformations of the two alditols1 and2 (3:2) obtained upon reduction of N-acetylneuraminic acid were determined in aqueous solution using proton and carbon nuclear magnetic resonance spectroscopy. Molecular mechanics calculation was proved to be not applicable onto alditols, if the balance of the conformational equilibrium is maintained by 1,3-diaxial interactions. No measurable amount of the α-N-acetylneuraminic acid like triple bent alditol form, which is believed to be the substrate of theClostridium perfringens lyase, could be detected in solution. In aqueous solution compound2 is present in its extended form. One can expect that the necessary energy contribution of approximately 1 kcal to fold2 into the form which is recognized by the enzyme is easily available.

The synthesis of 5-acetamido-2,6-anhydro-3,5-dideoxy-D- erythro-L-manno-nonic acid (3b, 7,8-epi2-2-d-2-HeqNeu5Ac) and sodium 5-acetamido-2,6-anhydro-3,5-dideoxy-L-threo-L-manno-nonate (6b, 8-epi-2-d-2-Heq-Neu5Ac) could be realized by transformation of 5-acetamido-3,5-dideoxy-L-glycero-L-altro-2-nonulopyranosonic acid (2a, 7,8-bis-epi-Neu5Ac) and 5-acetamido-3,5-dideoxy-3-L-glycero-D-galacto-2-nonulosonic acid (5a, 8-epi-Neu5Ac) into the corresponding peracetylated 2-chloro derivatives and subsequent catalytic hydrogenation. As this procedure could not be applied to the synthesis of the 7-epi, 7-deoxy and 8-deoxy derivatives a new strategy, which started with the methyl 5-acetamido-2,6-anhydro-3,5-dideoxy-D-erythro-L-manno-nonoate (1e), was designed. For this purpose, a gram-scale preparation of 1e was developed. Transformation of protecting groups and radical reduction of selectively introduced tolylthiocarbonate groups led to the corresponding 5-acetamido-2,6-anhydro-3,5,7-trideoxy-D-glycero-L-manno-nonoic acid (12b, 2,7-d2-2Heq-Neu5Ac) and sodium 5-acetamido-2,6-anhydro-3,5,8-trideoxy-D-glycero-L-manno-nonate (11b, 2,8-d2-2Heq-Neu5Ac). An oxidation — reduction sequence yielded 5-acetamido-2,6-anhydro-3,5-dideoxy-D-threo-L-manno-nonoic acid (9c, 2d-2Heq-7-epi-Neu5Ac). Also the sialic acid analog 6b could be prepared according to this newly designed strategy.

The reaction of peracetylated N-acetylneuraminic acid methyl ester 1 with nitrosyl acetate affords a mixture of anti/syn-N-nitroso derivatives 2a and 2a′, which can be transformed with sodium trifluoroethanolate into the 5-diazo compound 3. The reaction of 3 with tetrabutylammonium acetate/acetic acid yields methyl 2,4,5,7,8,9-hexa-O-acetyl-3-deoxy-D-clycero-β-D-galacto-2-nonulopyranosidonate (KDN) (4a). On the other hand, 5-azido-5-deoxy-KDN (5a) is formed by treating 3 with hydrazoic acid in toluene. Heating of 2a/2a′ in toluene furnishes a mixture of the peracetylated deaminated furanoid sialic acid derivative 10 with probably changed configuration at C-5 and C-6 and the deaminated 5,6- and 4,5-didehydrosialic acid derivatives 6 and 7. Catalytic hydrogenation of 6 and 7 yields the 5-deoxy-KDN derivative 9a and - after hydrogen-olysis of the 4-acetoxy group - a minor amount of compound 8. The compounds 4a, 5a, and 9a have been converted into the free deaminated sialic acids 4e, 5e, and 9e via the 4-me-thylumbelliferyl 2α-glycosides 4c, d, 5c, d, and 9c, d.

The methyl ester of N-acetylneuraminic acid β-methyl ketoside (Neu5Ac1Me-2β-Me) (1) is used as common starting material for the synthesis of the title compounds. Combined derivatization reactions with reagents thiophosgene, p-cresol, benzoyl chloride, and acetic anhydride/pyridine lead to the thiocarbonate derivatives 2, 6–8, and 12. Further transformation with iodomethane yields the 9-iodo compounds 3, 9, and 13, which are reduced by tributyltin hydride to the deoxy derivatives 4, 10, and 14. Hydrolysis of 14, 10, and 4 affords the desired 9-deoxy, 7,9-dideoxy-, and 4,7,9-trideoxy-N-acetylneuraminic acids 15 (9-d-Neu5Ac), 11 (7,9-d2-Neu5Ac), and 5 (4,7,9-d3-Neu5Ac), respectively. — The sialic acid analogues 11 and 5 were activated by CMP-sialate synthase [E,C.2.7.7.43] to an extent of 30–40 and 50–60%, respectively, relative to N-acetylneuraminic acid.

The 4-, 7-, and 8-oxo-sialic acid β-methyl ketosides 7, 10a, and 11a were obtained by transformation of easily available derivatives of N-acetylneuraminic acid (1a). The carbonyl migration from C-7 to C-8 can be carried out under well-defined conditions with formation of the ketone 11b. Starting from 7- and 8-ketones 17 and 20 the corresponding dimethyl acetals are prepared. The 4-ketone 7 behaves as a moderate competitive inhibitor of CMP-sialate synthase [EC 2.7.7.43], whereas the 8-ketone 11a, the 8,8-dimethyl acetal 19, and the 7,7-dimethyl acetal 23 prove not to be inhibitors of this enzyme. The 7-ketone 10a was not tested because of instability under test conditions at pH 8.5.

The key step in the preparation of 6-deoxy-1,2-O-isopropylidene-β-L-talofuranose (7) and 6-deoxy-1,2-O-isopropylidene-β-L-idofuranose (13) is the selective exchange of the 6-O-mesyl rest of 3-O-acetyl-5,6-O-dimesyl-1,2-O-isopropylidene-α-D-allofuranose (4) and 3-O-acetyl-5,6-O-dimesyl-1,2-O-isopropylidene-α-D-glucofuranose (10) by acetate group (potassium acetate/18-crown-6).

A 4-C-methylene sialic acid derivative 3 was obtained by the reaction of the corresponding 4-oxocompound 2 with CH 2 I/Zn/CP 2 ZrCl 2 . The product was transformed into a mixture of the 4-deoxy-4-(R)-methyl- and 4-(S)-methyl derivatives 4 and 5 . Sialic acids 6 and 7 were obtained after the removal of protective groups.

Readily available β-glycofuranosyl isocyanides1,2,4,5,6,18,19,20 are transformed into the corresponding protected tetrahydrofurans21,22,23,24,25,26 by means of tributyltin hydride andAIBN. The synthesis of18 and19 by dehydration of the formamide15 is described. Starting with 6-deoxy-1,2-O-isopropyliden-α-D-allofuranose (7) crystalline 1,2-O-diacetyl-3,5-dibenzoyl-β-D-allofuranose (9) is obtained.9 is first transformed into the anomeric azides11,12 and13,14 and subsequently into the formamide15.

1-(3′-Azido-2′,3′,5′-trideoxy-β-D-allofuranosyl)thymine 12 (homo-AZT) was synthesized starting from 1,2;5,6-di-O-isopropylidene- 3-O-mesyl-α-D-allofuranose 1 in an eleven step sequence (overall yield: 4%).

Starting from 3-O-mesyl-1,2-O-isopropylidene-alpha-D-allofuranose (9) the anomeric mixtures of the requisite carbohydrates 1,2-di-O-acetyl-6-O-benzoyl-5-deoxy-3-O-mesyl-D-allofuranoses++ + 17A alpha/beta, 1,2-di-O-acetyl-5,6-di-O-benzoyl-3-O-mesyl-D-allofuranoses 17B alpha/beta, and 1,2-di-O-acetyl-5,6-di-O-benzoyl-3-O-mesyl-L-talofuranoses 17C alpha/beta were synthesized. 1,2-Di-O-acetyl-5-O-benzoyl-6-deoxy-3-O-mesyl-D-allofuranoses++ + 17D alpha/beta and the corresponding L-talofuranoses 17E alpha/beta were obtained from 6-deoxy-3,5-di-O-benzoyl-1,2-O-isopropylidene-alpha-D- allofuranose (12) and the corresponding beta-L-talofuranose 13. Coupling of these sugar derivatives with thymine gave the beta-nucleoside derivatives 18A-E. Treatment of compounds 18A-E with DBU produced the corresponding 2,3'-anhydro nucleosides 19A-E with a free 2'-OH group. After deoxygenation of 2'-O-[[(4-methylphenyl)oxy]thiocarbonyl] compounds 20A-E with tributyltin hydride the 2,3'-anhydro bridge of the 2'-deoxynucleosides 21A-E was opened with LiN3 to produce the protected 3'-azido-2,3'-dideoxynucleoside derivatives 22A-G. Saponification with NaOCH3 gave 1-(3'-azido-2',3',5'-trideoxy-beta-D-allofuranosyl)thymine (2; homo-AZT), the 5'-C-(hydroxymethyl) derivatives of AZT 1-(3'-azido-2',3'- dideoxy-beta-D-allofuranosyl)thymine (3) and 1-(3'-azido-2',3'-dideoxy-alpha-L-talofuranosyl)thymine (4), and the 5'-C-methyl derivatives of AZT 1-(3'-azido-2',3',6'-trideoxy-beta-D-allofuranosyl)thymine (5) and 1-(3'-azido-2',3',6'-trideoxy-alpha-L-talofuranosyl)thymine (6). Compounds 2-6 were evaluated for their inhibitory effect on human immunodeficiency virus type 1 (HIV-1) and type 2 (HIV-2) replication in MT-4 cells and found inactive at subtoxic concentrations. Compounds 2-4 and 6 are not effective against herpes simplex virus type 1 (HSV-1) and type 2 (HIV-2), vaccinia virus (VV), and vesicular stomatitis virus (VSV) at 400 micrograms/mL. 5 is slightly active against HSV-1, HSV-2 and VV at 150, 300, and 300 micrograms/mL, respectively.

The initial step of influenza infection is binding of the virus particles via their hemagglutinin to cell-surface sialic acids. This study was initiated to elucidate the functional groups of the nine-carbon sialic acid molecule which interact with the hemagglutinin and contribute to the affinity of this sugar to the protein. In order to address this question, synthetic sialic acid analogues were tested in a virus adsorption inhibition assay for their inhibitory potency. Modifications in three regions of the sialic acid molecule were evaluated: the glycerol side chain (C7-C9), the N-acetyl group at C5, and the carboxy group (C1). In the glycerol side chain, the hydroxy groups at C7 and C8 appear to be important for binding through hydrogen bonds, whereas the hydroxyl at C9 does not appear to be involved. The N-acetyl group is critical for the interaction of sialic acid with the hemagglutinin. The results suggest that its contribution is mediated through hydrophobic interactions of the methyl group. Finally, the orientation of the carboxy group is essential for the binding of sialic acid to the hemagglutinin. The information gained in this study will be useful in developing novel compounds which bind more avidly to the influenza virus hemagglutinin. Such a strategy may contribute to the design of new anti-influenza drugs.

2,3-Didehydro-2-deoxy- N -trifluroacetylneuraminic acid (5-trifluoroacetyl-Neu2en) ( 3 ) has been synthesised from Neu5Ac2en ( 1 ) by hydrazinolysis, to give Neu2en ( 2 ), followed by N -trifluoroacetylation. 2,3-Didehydro-2,3-dideoxy- d - glycero - d - galacto -2-nonulopyranosonic acid (Kdn2en, 8 ) and 5-azido-2,3-didehydro-2,3,5-trideoxy- d - glycero - d - galacto -2-nonulopyranosonic acid (5-azido-5-deoxy-Kdn2en, 9 ) have been prepared from the acetylated methyl esters of Kdn ( 4 ) and 5-azido-5-deoxy-Kdn ( 5 ) via Zemplen saponification. The behaviour of the above 2,3-didehydro-2-deoxysialic acids towards Vibrio cholerae sialidase has been investigated