Strukturelle Abwandlungen an partiell silylierten Kohlenhydraten mittels Triphenylphosphin/Azodicarbonsäure-diäthylester. 3. Mitteilung [1]

Structural Modification on Partially Silylated Carbohydrates by Means of Triphenylphosphine/Diethyl Azodicarboxylate Reaction of methyl 2, 6-bis-O-(t-butyldimethylsilyl)-β-D -glucopyranoside ( 1a ) with triphenylphosphine (TPP)/diethyl azodicarboxylate (DEAD) and Ph₃P · HBr or methyl iodide yields methyl 3-bromo-2, 6-bis-O-(t-butyldimethylsilyl)-3-deoxy-β-D -allopyranoside ( 3a ) and the corresponding 3-deoxy-3-iodo-alloside 3c (Scheme 1). By a similar way methyl 2, 6-bis-O-(t-butyldimethylsilyl)-α-D -glucopyranoside ( 2a ) can be converted to the 4-bromo-4-deoxy-galactoside 4a and the 4-deoxy-4-iodo-galactoside 4b . In the absence of an external nucleophile the sugar derivatives 1a and 2a react with TPP/DEAD to form the 3,4-anhydro-α- or -β-D -galactosides 5 and 6a , respectively, while methyl 4, 6-bis-O-(t-butyldimethylsilyl)-β-D -glucopyranoside ( 1b ) yields methyl 2,3-anhydro-4, 6-bis-O-(t-butyldimethylsilyl)-β-D -allopyranoside ( 7a , s. Scheme 2). Even the monosilylated sugar methyl 6-O-(t-butyldimethylsilyl)-α-D -glucopyranoside ( 2b ) can be transformed to methyl 2,3-anhydro-6-O-(t-butyldimethylsilyl)-β-D -allopyranoside ( 8 ; 56%) and 3,4-anhydro-α-D -alloside 9 (23%, s. Scheme 3). Reaction of 1c with TPP/DEAD/HN₃ leads to methyl 3-azido-6-O-(t-butyldimethylsilyl)-3-deoxy-β-D -allopyranoside ( 10 ). The epoxides 7 and 8 were converted with NaN₃/NH₄Cl to the 2-azido-2-deoxy-altrosides 11 and 13 , respectively, and the 3-azido-3-deoxy-glucosides 12 and 14 , respectively (Scheme 4 and 5). Reaction of 7 and 8 with TPP/DEAD/HN₃ or p-nitrobenzoic acid afforded methyl 2,3-anhydro-4-azido-6-O-(t-butyldimethylsilyl)-4-deoxy-α- and -β-D -gulopyranoside ( 15 and 17 ), respectively, or methyl 2,3-anhydro-6-O-(t-butyldimethylsilyl)-4-O-(p-nitrobenzoyl)-α- and -β-D -gulopyranoside ( 16 and 18 ), respectively, without any opening of the oxirane ring (s. Scheme 6). - The 2-acetamido-2-deoxy-glucosides 19a and 20a react with TPP/DEAD alone to form the corresponding methyl 2-acetamido-3,4-anhydro-6-O-(t-butyldimethylsilyl)-2-deoxy-galactopyranosides ( 21 and 22 ) in a yield of 80 and 85%, respectively (Scheme 7). With TPP/DEAD/HN₃ 20a is transformed to methyl 2-acetamido-3-azido-6-O-(t-butyldimethylsilyl)-2,3-didesoxy-β-D -allopyranoside ( 25 , Scheme 8). By this way methyl 2-acetamido-3,6-bis-O-(t-butyldimethylsilyl)-α-D -glucopyranoside ( 19b ) yields methyl 2-acetamido-4-azido-3,6-bis-O-(t-butyldimethylsilyl)-2,4-dideoxy-α-D -galactopyranoside ( 23 ; 16%) and the isomerized product methyl 2-acetamido-4,6-bis-O-(t-butyldimethylsilyl)-2-deoxy-α-D -glucopyranoside ( 19d ; 45%). Under the same conditions the disilylated methyl 2-acetamido-2-deoxy-glucoside 20b leads to methyl 2-acetamido-4-azido-3,6-bis-O-(t-butyldimethylsilyl)-2,4-dideoxy-β-D -galactopyranoside ( 24 ). - All Structures were assigned by ¹H-NMR. analysis of the corresponding acetates.     

Sulfated 1, 6-AnhydrO-4-O-(β-D-Glucopyranosyluronate)-β-D-Glucopyranosyl Derivatives: Syntheses And Conformations

Abstract

A series of sulfated 1,6-anhydro-4-O-(β-D-glucopyranosyluronate)-β-D-glucopyranose derivatives 7 and 9-13 with different degrees of charge was synthesized from a common disaccharide precursor 1,6-anhydro-2-azido-2-deoxy-4-O-(methyl2,3-di-O-benzyl-β-D-glucopyransyl-uronate-β-D-glucopyranose (5). For the 1,6-anhydro-β-D-glucopyranose moiety of this compound a boat-chair equilibrium is found, the boat conformation being stabilized by an intramolecular hydrogen bridge. The fully sulfated β-D-glucopyranosyl-uronates 10 and 13 occur in unusual nonchair conformations.     

Non-Glycosidic Azides of D-Altro- and D-Gulopyranose

ABSTRACT

Starting with methyl 2-O-cyclohexylcarbamoyl-3,4-O-(2,2,2-trichloroethylidene)-α-D-altropyranoside (1), methyl 4-O-cyclohexylcarbamoyl-2,3-O-(2,2,2-trichloroethylidene)-β-D-gulopyranoside (12), and methyl 6-O-cyclohexylcarbamoyl-2,3-O-(2,2,2-trichloroethylidene)-β-D-gulopyranoside (21), the 6-azido-6-deoxyaltroses 4, 6, 11, the 6-azido-6-deoxy-D-gulose 14, the 4-azido-4,6-dideoxy-D-gulose 20, and the 4-azido-4-deoxy-D-gulose 26 were synthesised via iodinated or tosylated precursors. Additionally, two gluco-configured azides, the 3-azido-3,6-dideoxy-D-glucose (19) and the 3-azido-3-deoxy-D-glucose (25), were obtained besides the desired 4-azido-4-deoxy-D-gulosides 20 and 26, when methyl 6-deoxy-4-O-tosyl-β-D-gulopyranoside (18) and methyl 6-O-cyclohexylcarbamoyl-4-O-tosyl-β-D-gulopyranoside, respectively, were reacted with sodium azide. An X-ray analysis is presented for methyl 2,4-di-O-acetyl-3-azido-3,6-dideoxy-zl-D-glucose (19).     

THE SYNTHESIS OF SOME C-4 AND C-9 SUBSTITUTED DERIVATIVES OF KDN2EN METHYL ESTER

The synthesis of a number of C-4 and C-9 substituted derivatives of KDN2en methyl ester 2 is reported. 9-Deoxy-9-iodo, 9-azido-9-deoxy and 9-O-methyl derivatives of 2(compounds 5, 7and 9) were prepared from the corresponding 9-O-tosylate, methyl 2,6-anhydro-3-deoxy-9-O-p-toluenesulfonyl-D-glycero-D-galacto-non-2-enonate (3). These compounds have been fully characterised as the peracetates 6, 8 and 10. Treatment of 3 with KSAc gave the 9-thioacetyl derivative which was isolated as the peracetate 11. 4-C-Ethenyl-4-deoxy (14), 4-C-phenyl-4-deoxy (15) and 4-C-[1-(methoxycarbonyl)ethenyl]-4-deoxy (16) derivatives of 2were prepared via the palladium-catalysed coupling of the 4-epi-chloride, methyl 5,7,8,9-tetra-O-acetyl-2,6-anhydro-4-chloro-3,4-dideoxy-D-glycero-D-talo-non-2-enonate (12) with the appropriate organostannanes.     

Preparation of Some Glycosyl Amino Acid Building Blocks via Click Reaction and Construction of a Glycotetrapeptide Library Using Spot Synthesis

The copper-catalyzed 1,3-dipolar cycloaddition reaction between ethyl 2,3,4-tri-O-actetyl-6-azido-6-deoxy-1-thio-β -d-glucopyranoside (2), ethyl 2,3,4-tri-O-actetyl-6-azido-6-deoxy-1-thio-β -d-galactopyranoside (4), methyl 2,3,4-tri-O-acetyl-6-azido-6-deoxy-α -d-mannopyranoside (7), and methyl 2,3,6-tri-O-acetyl-2-azido-2-deoxy-β -d-glucopyranoside (9), and tert-butyl-protected Fmoc-asparaginic acid propargylamide (10) gave the corresponding protected glycosyl amino acid building blocks 11, 13, 15, and 17 in 67% to 95% yield. The latter were converted into the corresponding pentafluorophenyl esters 12, 14, 16, and 18, which were used for a spot synthesis of a combinatorial library containing 256 glycotetrapeptides. The library was screened for lectin-binding affinity with the lectins Concanavalin A (Con A), phaseolus vulgaris (PHA-E), and galantus nivalis (GNA).     

Trans Benzoyl Migration in 1.6-Anhydro-2-azido-4-O-benzoyl-2-deoxy-β-D-glucopyranose in Non-Aqueous Basic Medium

When 1,6-anhydro-2-azido-4-O-benzoyl-2-deoxy-β-D-glucopyranose (¹ (l) was treated with allyl bromide in benzene-tetrahydrofuran solution in the presence of sodium hydride, we obtained the expected reaction product, 3-O-allyl-1,6-anhydro-2-azido-4-O-benzoyl-2-deoxy-β-D-glucopyranose (2), and the rearranged compounds 1,6-anhydro-2-azido-3-O-benzoyl-2-deoxy-β-D-glucopyranose (3) and 4-O-allyl-1,6-anhydro-2-azido-3-O-benzoyl-2-deoxy-β-D-glucopyranose (4).     

BROMOHYDROXYLATION OF GLYCALS—AN INVESTIGATION INTO THE REACTION OF SOME 4-N-ACYLATED DERIVATIVES OF METHYL 5-ACETAMIDO-7,8,9-TRI-O-ACETYL-2,6-ANHYDRO-3,4,5-TRIDEOXY-D-GLYCERO-D-GALACTO-NON-2-ENONATE AND ITS 4-EPIMER

Bromohydroxylation of some 4-N-acylated derivatives of the glycals of N-acetylneuraminic acid, methyl 5-acetamido-7,8,9-tri-O-acetyl-2,6-anhydro-3,4,5-trideoxy-D-glycero-D-galacto-non-2-enonate (4) and methyl 5-aceta-mido-7,8,9-tri-O-acetyl-2,6-anhydro-3,4,5-trideoxy-D-glycero-D-talo-non-2-enonate (the 4-epimer of 4), with N-bromosuccinimide (NBS) and water in the presence of a co-solvent has provided a range of new glycosyl donors. The stereoselectivity of the halohydroxylation reaction was found to be governed by solvent composition, reaction temperature and the stereoelectronic nature of the substituent at C-4.     

Preparation of 3-Amino-3-Deoxy-2,4,5,6-Tetra-O-Methyl-D-Altronic Acid Hydrochloride,a Precursor in the Preparation of a Chiral β-Polyamide (Nylon 3 Analog)

ABSTRACT

3-Amino-3-deoxy-2,4,5,6-tetra-O-methyl-D-altronic acid hydrochloride was prepared from methyl 3-azido-3-deoxy-4,6-O-benzylidene-α-D-altropyranoside in seven steps. The key intermediate in this synthesis was the 3-acetamido-3-deoxy-2,4,6-tri-O-methyl-D-altrono-1,5-lactone which could be transformed, in one step, into methyl 3-acetamido-3-deoxy-2,4,5,6-tetra-O-methyl-D-altronate. However, attempts to open the 3-azido-3-deoxy-tri-O-methyl (or O-benzyl)-D-altrono-1,5-lactone intermediates gave a mixture of products, mostly, α,β-unsaturated carbonyl compounds. The 3-amino-3-deoxy-2,4,5,6-tetra-O-methyl-D-altronic acid could be transformed into the corresponding β-lactam, (3S,4R)-3-methoxy-4-(D-erythro-trimethoxypropyl) azetidine-2-one, which was further polymerized by anionic ring-opening polymerization giving poly[(2S,3R)-2-methoxy-3-(D-erythro-trimethoxypropyl) propanamide], a chiral nylon 3 analog.     

Application of Phenyl 1-Selenoglycosides in the Synthesis of a Cell-Wall Tetrameric Fragment of Proteus Vulgaris Strain 5/43

Abstract

DAST-assisted rearrangement of 3-O-allyl-4-O-benzyl-α-l-rhamnopyranosyl azide followed by treatment of the generated fluorides with ethanethiol and BF₃·OEt₂ gave glycosyl donor ethyl 3-O-allyl-2-azido-4-O-benzyl-2,6-dideoxy-1-thio-α/β-l-glucopyranoside. Stereoselective glycosylation of methyl 4,6-O-benzylidene-2-deoxy-2-phthalimido-β-D-glucopyranoside with ethyl 3-O-allyl-2-azido-4-O-benzyl-2,6-dideoxy-1-thio-α/β-l-glucopyranoside, under the agency of NIS/TfOH afforded methyl 3-O-(3-O-allyl-2-azido-4-O-benzyl-2,6-dideoxy-α-l-glucopyranosyl)-4,6-O-benzyli-dene-2-deoxy-2-phthalimido-β-D-glucopyranoside. Removal of the allyl function of the latter dimer, followed by condensation with properly protected 2-azido-2-deoxy-glucosyl donors, in the presence of suitable promoters, yielded selectively methyl 3-O-(3-O-[6-O-acetyl-2-azido-3,4-di-O-benzyl-2-deoxy-α-D-glucopyranosyl]-2-azido-4-O-benzyl-2,6-dideoxy-α-l-glucopyranosyl)-4,6-O-benzylidene-2-deoxy-2-phthalimido-β-D-glucopyranoside. Deacetylation and subsequent glycosylation of the free HO-6 with phenyl 2,3,4,6-tetra-O-benzoyl-1-seleno-β-D-glucopyranoside in the presence of NIS/TfOH furnished a fully protected tetrasaccharide. Deprotection then gave methyl 3-O-(3-O-[6-O-{β-D-glucopyranosyl}-2-acetamido-2-deoxy-β-D-glucopyranosyl)-2-acetamido-2,6-dideoxy-α-L-glucopyranosyl)-2-acetamido-2-deoxy-β-D-glucopyranoside.     

Synthesis of (Z)-3-Deoxy-3-(1,2,3,6-Tetradeoxy-3,6-Imino-L-Arabino-Hexitol-1-C-Ylidene)-D-Xylo-Hexose Derivatives. First Examples Of Homo-(1→3)-C-Linked Iminodisaccharides.

ABSTRACT

Cross-aldolisation of 3,6-[(tert-butoxy)carbonyl]imino-2,3,6-trideoxy-4,5-O-isopropylidene-L-arabino-hexose (10) with 1,6-anhydro-2-O-benzyl-3-deoxy-β-D-erythro-hexopyrano-4-ulose (6) generates, after water elimination, a single enone 11 that is reduced selectively into an allylic alcohol 12, deprotection of which affords methyl (Z)-3-deoxy-3-(1,2,3,6-tetradeoxy-3,6-imino-L-arabino-hexitol-1-C-ylidene)-β-D-xylo-hexofuranoside (1) and (Z)-1,6-anhydro-3-deoxy-3-(1,2,3,6-tetradeoxy-3,6-imino-L-arabino-hexitol-1-C-ylidene)-β-D-xylo-hexopyranose (14).     

Efficient synthesis of multifunctional furanoid C-glycoamino acid precursors

Ready access to constrained, multifunctionalized, hydrolytically stable amino acids has been established by the synthesis of their direct precursors using 2,5-anhydro-3-azido-3-deoxy-d-altrose (a ‘formyl azido-C-glycofuranoside’), or its readily available, stable synthetic equivalent [(1R) and (1S)-2,5-anhydro-3-azido-4,6-O-benzylidene-3-deoxy-1-fluoro-1-O-methyl-d-altritol], as novel molecular scaffolds.     

A New Synthesis of Methyl 3-Amino-3,4-dideoxy-β-D-xylo-hexopyranoside

Abstract

Benzylidenation of methyl β-D-glucopyranoside, followed by selective 3-O-tosylation, reductive acetal opening, chlorination, radical deoxygenation and transesterification, afforded methyl 2,3-anhydro-6-O-benzyl-4-deoxy-β-D-ribo-hexopyranoside 8. Subsequent epoxide opening with NaN₃ and catalytic hydrogenation led to the title compound.     

Stereoselective Glycosidic Coupling Reactions of Fully Benzylated 1,2-Anhydro Sugars with N-Tosyl- or N-Benzyloxycarbonyl-l-serine Methyl Ester

Abstract

The glycosidic coupling reaction of 1,2-anhydro-3,4,6-tri-O-benzyl-β-d-mannopyranose (7), 1,2-anhydro-3,4,6-tri-O-benzyl-α-d-galactopyranose (21), and 1,2-anhydro-3,4-di-O-benzyl-α-d-xylopyranose (18) with N-tosyl- (10) or N-benzyloxycarbonyl- (11) L-serine methyl ester provides a new stereocontrolled synthesis of 1,2-trans linked glycopeptides. The 1,2-anhydro sugars are shown to react smoothyl with 10 or 11 in the presence of Lewis acid (ZnCl₂ or AgOTf) as well as powdered 4A molecular sieves in CH₂Cl₂ at room temperature to afford glycosyl serine derivatives with high stereoselectivity and high yield in less than 30 min. An improved method using 2-O-acetyl-3,4,6-tri-O-benzyl-α-d-mannopyranosyl chloride (6) as the key intermediate for ring closure was applied for the synthesis of 1,2-anhydro-3,4,6-tri-O-benzyl-β-d-mannopyranose.     

SYNTHESIS OF 6-AMINO-6-DEOXY-2,3,4,5- TETRA-O-METHYL-D-GALACTONIC ACID,A KEY PRECURSOR OF A STEREOREGULAR POLYAMIDE[1]

The title compound (17) was synthesized by two alternative sequences, starting from D-galactose diacetonide (1) and from methyl 6-O-tosyl-α-D-galactopyranoside (9). Compound 1 was converted into the 6-bromo-6-deoxy derivative 2 or mesylated to 3. Nucleophilic substitution of the leaving group in 2 and 3 by sodium azide led to the 6-azido-6-deoxy derivative 4, which on treatment with methanol under acidic conditions afforded a mixture of the corresponding methyl β-furanoside (5) and α-pyranoside (6). Methylation of the free hydroxyl groups of 5 and 6 gave the respective per-O-methyl derivatives 7 and 8. In order to maintain the size of the sugar ring during the sequence, compound 8 was alternatively prepared from 9, by acetylation, substitution by azide and per-O-methylation. Hydrolysis of the glycoside followed by oxidation and further 5-O-methylation afforded the 6-azido-6-deoxy carboxylic acid 16 which was converted into 17 (38% overall yield from 9) by hydrogenolysis of the azide function.     

Preparation of 2-Azido-4-O-benzoyl-2,6-dideoxy-3-O-methyl-β-D-allopyranose and Its Disaccharide Derivative

Abstract

2-Azido-4-O-benzoyl-2,6-dideoxy-3-O-methyl-D-allopyranose, needed as one of the building blocks for construction of a novel cyclodextrin-like compound, was prepared in the form of crystalline β-anomer 6 from methyl 2-azido-4,6-O-benzylidene-2-deoxy-α-D-allopyranoside 1. As a model of α-glycosidation necessary for formation of a cyclic structure, 6 was converted into the corresponding β-glycosyl trichloroacetimidate and coupled with methyl 6-O-benzyl-2,3-di-O-methyl-α-D-glucopyranoside 8, giving α(1→4)-linked disaccharide derivative 9.     

Syntheses of 2,6-Anhydro-3-Deoxy-D-Glycero-D-Galacto-Non-2-Enonic Acid (Kdn2En) and Its Hydrogenation Products 1

Abstract

Methyl 4,5,7,8,9-penta-O-acetyl-2,6-anhydro-3-deoxy-D-glycero-D-galacto-enonate (5) was synthesized from KDN methyl ester 2 with a catalytic amount of concentrated sulfuric acid in acetic anhydride, or from 2-chloro-KDN methyl ester 4 with DBU in good yield. Hydrogenation of 4 and 5 with 10% Pd-C gave 2-deoxy-2-H_ax-KDN 8 and 2-deoxy-2-H_eq-KDN derivative 11 in high yield, respectively. The structures of these compounds were elucidated from the MS, elemental analysis, ¹H NMR and ¹³C NMR data.

     

Structure of 1,5-Anhydro-D-fructose: X-ray Analysis of Crystalline Acetylated Dimeric Forms

Abstract

Acetylation of 1,5-anhydro-D-fructose under acidic conditions gave two crystalline acetylated dimeric forms, which by X-ray analysis were shown to be diastereomeric spiroketals formed between C-2 and C-2/C-3. The structures of the compounds differed only at the configuration at C-2. Acetylation or benzoylation of 1,5-anhydro-D-fructose in pyridine yielded 3,6-di-O-acetyl-1,5-anhydro-4-deoxy-D-glycero-hex-3-enos-2-ulopyra-nos or crystalline 1,5-anhydro-3,6-di-O-benzoyl-4-deoxy-D-glycero-hex-3-enos-2-ulo-pyranose.

     

Synthetic Studies on Sialoglycoconjugates 81: Synthesis of Positional Isomers of Sialyl Lewis X Epitope Containing 1-Deoxy-d Glucose in Place of N-Acetylglucosamine,and Their Inhibitory Activity to Selectin-Mediated Adhesion

Abstract

Three sialyl-Le^x epitope analogs, which carry fucose and α-sialyl-(2→3)-galactose residues at O-2 and O-3, O-3 and O-2, and O-4 and O-6 positions of 1-deoxy-D-glucose backbone, respectively, have been synthesized. Glycosylation of 1,5-anhydro-4,6-O-benzylidene-D-glucitol (1) or 1,5-anhydro-6-O-benzoyl-2,3-di-O-benzyl-d-glucitol (4) prepared from 1,5-anhydro-d-glucitol, with methyl 2,3,4-tri-O-benzyl-1-thio-β-L-fucopyranoside (5) using dimethyl(methylthio)sulfonium triflate (DMTST) as a promoter, afforded the corresponding fucosyl 1,5-anhydro-d-glucitol derivatives 7, 8 and 9. Glycosylation of 7, 8 or 10 derived from 9, with methyl O-(methyl 5-acetamido-4,7,8,9-tetra-O-acetyl-3,5-dideoxy-d-glyceroα-d-galacto-2-nonulopyranosylonate)-(2→3)-2,4,6-tri-O-benzoyl-1-thio-β-d-galactopyranoside (11) in the presence of DMTST gave the expected tetrasaccharide derivatives 12, 16 and 20. Hydrolysis of the benzylidene group in 12 and 16 gave compounds 13 and 17. Finally 13, 17 and 20 were transformed, by reductive removal of the benzyl groups, O-deacylation and subsequent hydrolysis of the methyl ester, into the sialyl-Le^x epitope analogs 15, 19 and 22, respectively.     

Synthesis of stereoregular heteropolysaccharides having amino-groups by ring-opening copolymerization of 1,6-anhydro-azido-sugar derivatives

The cationic, ring-opening copolymerization of 1,6-anhydro-2-azido-3,4-di-0-benzyl-2-deoxy-(2-ABG), -3-azido-2,4-di-0-benzyl-3-deoxy- (3-ABG), -4-azido-2,3-di-0-benzyl-4-deoxy-β-D -glucopyranose (4-ABG) with 1,6-anhydro-2,3,4-tri-0-benzyl-β-D -glucopyranose (LGTBE) was investigated with phosphorus pentafluoride as catalyst at low temperatures, giving highly stereoregular, (1→6)-α-linked copolymers with number-average molecular weights of 3.90 × 10⁴?9.27 × 10⁴. Structure and composition of the copolymers were determined by ¹H- and ¹³C-NMR spectroscopies and elemental analysis, which indicated that copolymerization occurred in a stereoregular manner to give azido groups containing (1→6)-α-linked glucopyranan derivatives. The differences in polymerizability among the three azido monomers are discussed. Regioselective reduction of three kinds of heteropolysacharide derivatives which had different quantities of azido groups at C-2, -3, or -4 position with lithium aluminum hydride and subsequent debenzylation of the copolymers with sodium in liquid ammonia produced amino-group-containing heteropolysaccharides.     

A Facile Synthesis of Prumycin

Abstract

Benzyl 2,3-anhydro-4-azido-4-deoxy-α-L-ribopyranoside (7), an intermediate for the synthesis of Prumycin was synthesized in 72% yield in seven steps from D-arabinose. Ammonolysis of 7 followed by N-protection with the benzyloxycarbonyl group gave benzyl 4-azido-2-(benzyloxycarbonyl)amino-2,4-dideoxy-α-L-arabinopyranoside (8), which was easily converted to Prumycin.