Synthesis of methyl α- and β-maltotriosides and aryl β-maltotriosides

Reaction of β-maltotriose hendecaacetate with phosphorus pentachloride gave 2′,2″,3,3′,3″,4″,6,6′,6″,-nona-O-acetyl-(2)-O-trichloroacetyl-β-maltotriosyl chloride (2) which was isomerized into the corresponding α anomer (8). Selective ammonolysis of 2 and 8 afforded the 2-hydroxy derivatives 3 and 9, respectively; 3 was isomerized into the α anomer 9. Methanolysis of 2 and 3 in the presence of pyridine and silver nitrate and subsequent deacetylation gave methyl α-maltotrioside. Likewise, methanolysis and O-deacetylation of 9 gave methyl β-maltotrioside which was identical with the compound prepared by the Koenigs—Knorr reaction of 2,2′,2″,3,3′,3″,4″,6,6′,6″-deca-O-acetyl-α-maltotriosyl bromide (12) with methanol followed by O-deacetylation. Several substituted phenyl β-glycosides of maltotriose were also obtained by condensation of phenols with 12 in an alkaline medium. Alkaline degradation of the o-chlorophenyl β-glycoside decaacetate readily gave a high yield of 1,6-anhydro-β-maltotriose.     

Studies on dextranases. 3. Insolubilization of a bacterial dextranase

Ammonium hydroxide treatment of 1,6:2,3-dianhydro-4-O-benzyl-β-D-mannopyranose, followed by acetylation, gave 2-acetamido-3-O-acetyl-1,6-anhydro-4-O-benzyl-2-deoxy-β-D-glucopyranose which was catalytically reduced to give 2-acetamido-3-O-acetyl-1,6-anhydro-2-deoxy-β-D-glucopyranose (6), the starting material for the synthesis of (1→4)-linked disaccharides bearing a 2-acetamido-2-deoxy-D-glucopyranose reducing residue. Selective benzylation of 2-acetamido-1,6-anhydro-2-deoxy-β-D-glucopyranose gave a mixture of the 3,4-di-O-benzyl derivative and the two mono-O-benzyl derivatives, the 4-O-benzyl being preponderant. The latter derivative was acetylated, to give a compound identical with that just described. For the purpose of comparison, 2-acetamido-4-O-acetyl-1,6-anhydro-2-deoxy-β-D-glucopyranose has been prepared by selective acetylation of 2-acetamido-1,6-anhydro-2-deoxy-β-D-glucopyranose.Condensation between 2,3,4,6-tetra-O-acetyl-α-D-glucopyranosyl bromide and 6 gave, after acetolysis of the anhydro ring, the peracetylated derivative (17) of 2-acetamido-2-deoxy-4-O-β-D-glucopyranosyl-α-D-glucopyranose. A condensation of 6 with 3,4,6-tri-O-acetyl-2-deoxy-2-diphenoxyphosphorylamino-α-D-glucopyranosyl bromide likewise gave, after catalytic hydrogenation, acetylation, and acetolysis, the peracylated derivative (21) of di-N-acetylchitobiose.     

Chemical Syntheses of 4-O-α and -β-D-galactopyranosyl-D-galactose and 3-O-α- and -β-D-galactopyranosyl-D-galactose

Reaction of 2,3-di-O-acetyl-1,6-anhydro-β-D-galactopyranose (2) with 2,3,4,6-tetra- O-acetyl-α-D-galactopyranosyl bromide in the presence of mercuric cyanide and subsequent acetolysis gave 1,2,3,6-tetra-O-acetyl-4-O-(2,3,4,6-tetra-O-acetyl-α-D-galactopyranosyl)-α-D-galactopyranose (4, 40%) and 1,2,3,6-tetra-O-acetyl-4-O-(2,3,4,6-tetra-O-acetyl-β-D-galactopyranosyl)-α-D-galactopyranose (5, 30%). Similarly, reaction of 2,4-di-O-acetyl-1,6-anhydro-β-D-galactopyranose (3) gave 1,2,4,6-tetra-O-acetyl-3-O-(2,3,4,6-tetra-O-acetyl-α-D-galactopyranosyl)-α-D-galactopyranose (6, 46%) and 1,2,4,6-tetra-O-acetyl-3-O-(2,3,4,6-tetra-O-acetyl-β-D-galactopyranosyl)-α-D-galactopyranose (7, 14%). The anomeric configurations of 4-7 were assigned by n.m.r. spectroscopy. Deacetylation of 4-7 afforded 4-O-α-D-galactopyranosyl-D-galactose (8), 4-O-β-D-galactopyranosyl-D-galactose (9), 3-O-α-D-galactopyranosyl-D-galactose (10), and 3-O-β-D-galactopyranosyl-D-galactose (11), respectively.     

Nitrous acid deamination of conformationally inverted aminodeoxyhexopyranoses

Nitrous acid deamination of 2-amino-1,6-anhydro-2-deoxy-β-D-glucopyranose (1) in the presence of weakly acidic, cation-exchange resin gave 1,6:2,3-dianhydro-β-D-mannopyranose (3) and 2,6-anhydro-D-mannose (6), characterized, respectively, as the 4-acetate of 3 and the per-O-acetylated reduction product of 6, namely 2,3,4,6- tetra-O-acetyl-1,5-anhydro-D-mannitol, obtained in the ratio of 7:13. Comparative deaminatior of the 4-O-benzyl derivative of 1 led to similar qualitative results. Deamination of 3-amino-1,6-anhydro-3-deoxy-β-D-glucopyranose gave 1,6:2,3- and 1,6:3,4-dianhydro-β-D-allopyranose (13 and 16), characterized as the corresponding acetates, obtained in the ratio of 31:69, as well as the corresponding p-toluenesulfonates. Deamination of 4-amino-1,6-anhydro-4-deoxy-β-D-glucopyranose and of its 2-O-benzyl derivative gave the corresponding 1,6:3,4-D-galacto dianhydrides as the only detectable products. 2,5-Anhydro-D-glucose, characterized as the 1,3,4,6-tetra-O- acetyl derivative of the corresponding anhydropolyol, was obtained in 39% yield from the same deamination reaction performed on 2-amino-1,6-anhydro-2-deoxy-β-D- mannopyranose (24). In 90% acetic acid, the nitrous acid deamination of 24, followed by per-O-acetylation, gave only 1,3-4-tri-O-acetyl-2,5-anhydro-α-D-glucoseptanose. In the case of 1,6-anhydro-3,4-dideoxy-3,4-epimino-β-D-altropyranose, only the corresponding glycosene was formed, namely, 1,6-anhydro-3,4-dideoxy-β-D-threo--hex-3-enopyranose.     

Studies related to the synthesis of derivatives of 2,6-diamino-2,3,4,6-tetradeoxy-D-erythro-hexose (purpurosamine C), a component of gentamicin C12

Reduction of 1,6-anhydro-3,4-dideoxy-β-D-glycero-hex-3-enopyranos-2-ulose (levoglucosenone) with lithium aluminium hydride afforded principally 1,6-anhydro-3,4-dideoxy-β-D-threo-hex-3-enopyranose (3), which was converted into 3,4-dihydro-2(S)-hydroxymethyl-2H-pyran (8) following acid-catalysed methanolysis and reductive rearrangement of the resulting α-glycoside 4 with lithium aluminium hydride. 1,6-Anhydro-3,4-dideoxy-2-O-toluene-p-sulphonyl-β-D-threo-hexopyranose, prepared from 3, reacted slowly with sodium azide in hot dimethyl sulphoxide to give 1,6-anhydro-2-azido-2,3,4-trideoxy-β-D-erythro-hexopyranose, which was transformed into a mixture of methyl 2-acetamido-6-O-acetyl-2,3,4-trideoxy-α-D-erythro-hexopyranoside (10) and the corresponding β anomer following acid-catalysed methanolysis, catalytic reduction, and acetylation. Acid treatment of methyl 4,6-O-benzylidene-3-deoxy-α-D-erythro-hexopyranosid-2-ulose yielded the enone 15, which was readily transformed into methyl 6-O-acetyl-3,4-dideoxy-α-D-glycero-hexopyranosid-2-ulose (19). Procedures for the conversions of DL-8, 10, and 19 into methyl 2,6-diacetamido-2,3,4,6-tetradeoxy-α-D-erythro-hexopyranoside (methyl N,N′-di-acetyl-α-purpurosaminide C) have already been described.     

Synthesis of a 4′-amino-4′,6′-dideoxymaltose derivative as a synthon of an α- d-glucosidase inhibitor

4′-Amino-1,6-anhydro-2,3,2′,3′-tetra-O-benzyl-4′,6′-dideoxy-β-maltose, required as a synthon for the preparation of an α- d-glucosidase inhibitor constituted of a basic pseudotrisaccharide, was prepared from 1,6-anhydromaltose ( 2). Two pathways were examined for introducing the amino function into 2 during that synthesis.     

Umlagerungsreaktionen bei der einwirkung von trifluormethansulfonsäure auf 2,3,4-tri-O-acetyl-1,6-anhydro-β-D-talopyranose-und 2,3,4-tri-O-acetyl-1,6-anhydro-β-D-glucopyranose

2,3,4-Tri-O-acetyl-1,6-anhydro-,β-D-talopyranose gave, in the presence of trifluoromethanesulfonic acid, the two talo ions 7 and 8, which are formed in approximately equal amounts. The hydrolytic ring-opening of the two ions proceeds stereoselectively. From 7 was formed 2,3-di-O-acetyl-1,6-anhydro-β-D-talopyranose and from 8 3,4-di-O-acetyl-1,6-anhydro-β-D-talopyranose, both having an axial, acetoxyl group. The talo ion 9 can undergo ring-contraction to the 1,6-anhydrotalofuranose ion 2. The doubly ring-contracted 1,5-anhydrotalofuranose ion 3, which can arise from 2 and 8, was also formed, and afforded the tri-O-acetyl derivatives of the furanose compounds 5 and 11. The mechanism of the ring-contraction reactions is discussed. 2,3,4-Tri-O-acetyl-1,6-anhydro-β-D-glucopyranose gave preferentially with trifluoromethanesulfonic acid and antimony pentachloride the manno ion 33, which rearranged for the most part into the altro ion 34. The equilibrium between the manno ion 33 and the altro ion 34 is approximately 1:3.     

Synthesis of derivatives of methyl β-sophoroside

Selective tritylation of methyl β-sophoroside (1) and subsequent acetylation gave the 3,4,2′,3′,4′-penta-O-acetyl-6,6′-di-O-trityl derivative, which was O-detritylated, and the product p-toluenesulfonylated, to give methyl 3,4,2′,3′,4′-penta-O-acetyl-6,6′-di-O-p-tolylsulfonyl-β-sophoroside (4) in 63% net yield. Compound 4 was also obtained in 69% yield by p-toluenesulfonylation of 1, followed by acetylation. Several, 6,6′-disubstituted derivatives of 1 were synthesized by displacement reactions of 4 with various nucleophiles. Treatment of 4 with sodium methoxide afforded methyl 3,6:3′,6′-dianhydro-β-sophoroside. Several 6- and 6′-monosubstituted derivatives of 1 were prepared, starting from the 4,6-O-benzylidene derivative of 1.     

The stepwise synthesis of a methyl β-xylotetraoside related to branched xylans

3,4-Di-O-acetyl-2-O-benzyl-α-d-xylopyranosyl bromide (1) reacts with methyl 2,3-anhydro-α-d-ribopyranoside (2) to afford, in high yield, methyl 2,3-anhydro-4-O- (3,4-di-O-acetyl-2-O-benzyl-β-d-xylopyranosyl)-β-d-ribopyranoside (3). Deacetylation of 3 gave 4, which reacted with 2,3,4-tri-O-acetyl-α-d-xylopyranosyl bromide to give the branched tetrasaccharide derivative 5, which, in turn, was converted by a series or conventional reactions into methyl 4-O-[3,4-di-O-(β-d-xylopyranosyl)-β-d- xylopyranosyl]-β-d-xylopyranoside. The reaction of 1 with its hydrolysis product gave 3,4-di-O-acetyl-2-O-benzyl-α-d-xylopyranosyl 3,4-di-O-acetyl-2-O-benzyl-β-d-xylopyranoside, which was also isolated after the reaction of 1 with 2.     

A convenient synthesis of 6′-C-substituted β-maltose heptaacetates and of panose

Benzylidenation of β-maltose monohydrate with α,α-dimethoxytoluene in N,N-dimethylformamide in the presence of p-toluenesulfonic acid gave, in 70% yield, 4′,6′-O-benzylidenemaltose, which was acetylated to afford, 1,2,3,6,2′,3′-hexa-O-acetyl-4′,6′-O-benzylidene-β-maltose (4). Removal of the benzylidene group of 4 gave 1,2,3,6,2′,3′-hexa-O-acetyl-β-maltose (5), which was transformed into 1,2,3,6,2′,3′,4′-hepta-O-acetyl-6′-O-p-tolylsulfonyl-β-maltose (8). Several 6′-substituted β-maltose heptaacetates were synthesized by displacement reactions of 8 with various nucleophiles. Condensation of 5 with 2,3,4,6-tetra-O-benzyl-α-d-glucopyranosyl bromide, under catalysis by halide ion, followed by removal of protecting groups, furnished panose in good yield.     

Synthesis of 2,4-diacetamido-2,4,6-trideoxy-L-altrose, -L-idose, and -L-talose from benzyl 6-deoxy-3,4-O-isopropylidene-beta-L-galactopyranoside

Acetylation of benzyl 6-deoxy-3,4O-isopropylidene-β-L-galactopyranoside gave benzyl 2-O-acetyl-6-deoxy-3,4-O-isopropylidene-β-L-galactopyranoside (1). Removal of the isopropylidene group afforded benzyl 2-O-acetyl-6-deoxy-β-L-galactopyranoside (2), which was converted into benzyl 2-O-acetyl-6-deoxy-3,4-di-O-(methyl-sulfonyl)-β-L-galactopyranoside (3). Benzyl 2,3-anhydro-6-deoxy-4-O-(methyl-sulfonyl)-β-L-gulopyranoside (4) was obtained from 3 by treatment with alkali. Reaction of 4 with sodium azide in N,N-dimethylformamide gave a mixture of two isomeric benzyl 2,4-diazido-2,4,6-trideoxy hexoses, the syrupy diazido derivative 5 and the crystalline benzyl 2,4-diazido-2,4,6-trideoxy-β-L-idopyranoside (6). Acetylation of 6 afforded a compound whose n.m.r. spectrum was completely first order and in agreement with the structure of benzyl 3-O-acetyl-2,4-diazido-2,4,6-trideoxy-β-L-idopyranoside (7). Lithium aluminium hydride reduction of 5, followed by acetylation, afforded a crystalline product (8), shown by n.m.r. spectroscopy to be benzyl 2,4-diacetamido-3-O-acetyl-2,4,6-trideoxy-β-L-altropyranoside. Similar treatment of the diazido derivative 6 afforded benzyl 2,4-diacetamido-3-O-acetyl-2,4,6-trideoxy-β-L-idopyranoside (9). Compounds 8 and 9 could also be obtained from 4 by treatment of the crude diazido mixture with lithium aluminium hydride, with subsequent N-acetylation. The syrupy benzyl 2,4-diacetamido-2,4,6-trideoxy-β-L-altropyranoside (10) and the crystalline benzyl 2,4-diacetamido-2,4,6-trideoxy-β-L-idopyranoside (11) thus obtained were then O-acetylated to give 8 and 9 respectively. Benzyl 2,4-diacetamido-2,4,6-trideoxy-β-L-talopyranoside (15) was obtained from 11 by treatment with methanesulfonyl chloride and subsequent solvolysis. Compound 15 was O-acetylated to yield benzyl 2,4-diacetamido-3-O-acetyl-2,4,6-trideoxy-β-L-talopyranoside (16). the n.m.r. spectrum of which was in full agreement with the assigned structure. The mass spectra of compounds 8–11, 15, and 16 were also in agreement with their proposed structures. Removal of the benzyl groups from 10, 11 and 15 afforded the corresponding 2,4-diacetamido-2,4,6-trideoxyhexoses 12, 13, and 17, having the L-altro, L-ido, and L-talo configurations, respectively.     

Enzymatic regioselective and complete deacetylation of two arabinonucleosides

Candida antarctica lipase B (CAL-B)-catalysed regioselective deacetylation of 2′,3′,5′-tri-O-acetyl-1-β-d-arabinofuranosyluracil (1) and 2′,3′,5′-tri-O-acetyl-9-β-d-arabinofuranosyladenine (2) was studied. The choice of the reaction medium allowed the regioselective formation of products bearing different degree of acetylation: in isopropanol, CAL-B catalysed the formation of the corresponding 2′-O-acetylated arabinonucleosides, while hydrolyses afforded the 2′,3′-di-O-acetylated products. In particular, the procedure herein described allows a simple and efficient preparation of the reported vidarabine prodrug 2′,3′-di-O-acetyl-9-β-d-arabinofuranosyladenine, avoiding the utilisation of protective groups. Moreover, to achieve full deacetylation of the assayed substrates, a set of commercial hydrolases and fungal keratinases from Doratomyces microsporus (DMK) and Paecilomyces marquandii (PMK) were tested. While only PMK and DMK catalysed the quantitative complete deacetylation of 1, DMK accomplished full deacetylation of 2 in shorter time than the other assayed enzymes.     

Sucrochemistry : Part X. 1′,4,6′-tri-O-mesylsucrose penta-acetate: A comparison of the reactivity at the 4 and 1′ positions

The 1′,4,6′-trisulphonate 2, obtained by mesylation of sucrose 2,3,3′,4′,6-penta-acetate (1), undergoes nucleophilic substitution with sodium benzoate in hexamethylphosphoric triamide at positions 1′,4, and 6′ to give 1,6-di-O-benzoyl-β-D-fructofuranosyl 4-O-benzoyl-α-D-galactopyranoside penta-acetate (3), and selectively at positions 4 and 6′ to give 6-O-benzoyl-1-O-mesyl-β-D-fructofuranosyl 4-O-benzoyl-α-D-galactopyranoside penta-acetate (4). The products 3 and 4 were identified from their ¹H-n.m.r. spectra and by O-deacylation to give β-D-fructofuranosyl α-D-galactopyranoside (5) and its 1-methanesulphonate 6, respectively. Treatment of the trisulphonate 2 with sodium azide gave analogous products, namely, 1,6-diazido-1,6-dideoxy-β-D-fructofuranosyl 4-azido-4-deoxy-α-D-galactopyranoside penta-acetate (8) and 6-azido-6-deoxy-1-O-mesyl-β-D-fructofuranosyl 4-azido-4-deoxy-α-D-galactopyranoside penta-acetate (7).     

A short synthesis of 4-deoxy-4-fluoroglucosaminides: Methylumbelliferyl N-acetyl-4-deoxy-4-fluoro-β-D-glucosaminide

A convenient method of synthesis of 1,6-anhydro-4-deoxy-2-O-tosyl-4-fluoro-β-D-glucopyranose by fusion of 1,6;3,4-dianhydro-2-O-tosyl-β-D-galactopyranose with 2,4,6-trimethylpyridinium fluoride was found. By a successive action of ammonia, methyl trifluoroacetate, and acetic anhydride, the resulting compound was transformed into 1,6-anhydro-3-O-acetyl-2,4-dideoxy-2-trifluoroacetamido-4-fluoro-β-D-glucopyranose, which was converted into 3,6-di-O-acetyl-2,4-dideoxy-2-trifluoroacetamido-4-fluoro-αD-glucopyranosyl fluoride by the reaction with HF/Py. The resulting fluoride was further used as a glycosyl donor in the synthesis of methylumbelliferyl N-acetyl-4-deoxy-4-fluoro-β-D-glucosaminide.     

18-Norspirostanol derivatives from Trillium tschonoskii

Three 18-norspironstanol oligoglycosides partly acylated in their sugar moieties were isolated from the underground parts of Trillium tschonoskii. Their structures were characterized, as 1-O-[2″,3″,4″-tri-O-acetyl-α-l-rhamnopyranosyl-(1 → 2)-α-l-arabinopyranosyl]-epitrillenogenin-24-O-acetate, 1-O-[2″,3″,4″-tri-O-acetyl-α-l-rhamno-pyranosyl-(1 → 2)-α-l-arabinopyranosyl]-epitrillenogenin and 1-O-[2″,4″-di-O-acetyl-α-l-rhamnopyranosyl-(1 → 2)-α-l-arabinopyranosyl]-epitrillenogenin-24-O-acetate.     

Some observations on the selective benzoylation of maltose and its derivatives

Benzoylation of β-maltose monohydrate (2) with 10 mol. equiv. of benzoyl chloride in pyridine at ?40° gave 1,2,6-tri-O-benzoyl-4-O-(2,3,4,6-tetra-O-benzoyl-α-D-glucopyranosyl)-β-D-glucopyranose (5) in 87% yield, without the need for column chromatography. Similarly, benzoylation of 2 with 8 mol. equiv. of reagent afforded the octabenzoate 5, and the 1,2,6,2′,3′,6′-hexabenzoate 11 in 3%, 79%, and 12% yield, respectively. Methyl 2,6,2′,3′,4′,6′-hexa-O-benzoyl-β-maltoside (10) was directly isolated as a crystalline monoethanolate in 83% yield, from the reaction mixture obtained by the benzoylation of methyl β-maltoside monohydrate (8) with 8.9 mol. equiv. of reagent. Benzoylation of 8 with 7 mol. equiv. of reagent produced 10 and the 2,6,2′,3′,6′-pentabenzoate 16 in 71% and 23% yield, respectively. The order of reactivity of the hydroxyl groups in methyl 4′,6′-O-benzylidene-β-maltoside towards benzoylation is HO-2, HO-6>HO-2′ ≈ HO-3′>HO-3. Benzoylation of methyl β-cellobioside (33) with 7.9 mol. equiv. of reagent gave the heptabenzoate and the 2,6,2′,3′,4′,6′-hexabenzoate 36 in 56% and 27% yield, respectively. Compounds 5, 16, and 36 were transformed into 4-O-α-D-glucopyranosyl-D-allopyranose, methyl 4-O-α-D-galactopyranosyl-β-D-allopyranoside, and methyl 4-O-β-D-glucopyranosyl-β-D-allopyranoside, respectively, by sequential sulfonylation, nucleophilic displacement, and O-debenzoylation.     

5-thio-l-rhamnose

Two routes for the synthesis of methyl 5-S-acetyl-6-deoxy-2,3-O-isopropylidene-5-thio-l-mannofuranoside (8) have been examined. Reaction of l-rhamnose with methanol in the presence of the cation-exchange resin gives methyl 6-deoxy-α-l-mannofuranoside (2), which on conventional acetonation yields methyl 6-deoxy-2,3-O- isopropylidene-α-l-mannofuranosides (3). Compounds 3 is also obtained by acetonation of l-rhamnose followed by treatment with a mixture of methanol, acetonation, Amberlite IR-120(H⁺) resin. Chlorination of 3 with triphenylphosphine-carbon tetrachloride gives methyl 5-chloro-5,6-dideoxy-2,3-O-isopropylidene-β-d-gulofuranoside (7), which reacts with potassium thioacetate to give 8. Alternatively, 3 is iodized with ruthenium tetraoxide to methyl 6-deoxy-2,3-O-isopropylidene-α-l-lyxo-hexofuranosid-5-ulose (9), which reduced by sodium borohydride mainly to methyl 6-deoxy-2,3-O-isopropylidene-β-d-gulofuranoside (10). The O-tosyl derivative of 10 reacts with potassium thioacetate to produced 8. Hydrolysis of 8 with 90% aqueous triflouroacetic acid, followed by acetolysis with a solution of acetic acid, acetic anhydride, and sulfuric acids gives an anomeric mixture of 1,2,3,4,-tetra-O-acetyl-6-deoxy-5-thio-l-mannopyranoses (12), together with a small proportion of 1,2,3,-tri-O-acetyl-5-S-acetyl-6-deoxy-5-thio-β-l-mannofuranose (13). Deacetylation of 12 or 13 gives 5-thio-l-rhamnose (6), from which crystalline 1,2,3,4-tetra-O-(p-nitrobenzoyl)-5-thio-β-l-rhamnopyranose (14) is obtained.     

1,4-anhydride formation of solvolysis of 1,6-disubstituted derivatives of 2,3,4,5-tetra-O-acetylallitol

The 6-O-mesyl, 6-O-tosyl, 6-bromo-6-deoxy, and 6-deoxy-6-iodo derivatives of 1,4-anhydro-DL-allitol were obtained by treatment of the corresponding 1,6-di-substituted derivatives (2, 3, 6, 4) of 2,3,4,5-tetra-O-acetylallitol with hot, methanolic hydrogen chloride. Compounds 2 and 3 were prepared by the acetolysis of the 1,6-di-O-mesyl and 1,6-di-O-tosyl derivatives (8 and 11) of di-O-benzylideneallitol. Iodide displacement on 2 gave 4, and detritylation-bromination of 2,3,4,5-tetra-O-acetyl-1,6-di-O-tritylallitol (5) gave 6. The acetal residues of di-O-benzylideneallitol have been shown to span the secondary carbon atoms.     

Chemical modification of aminocyclitol antibiotics

The aminocyclitol antibiotic neamine has been chemically modified at the hydroxyl group on C-6 of the 2-deoxystreptamine moiety. The partially acetylated neamine derivatives, 6,3′,4′-tri-O-acetyl- (3) and 5,3′,4′-tri-O-acetyl-1,3,2′,6′-tetra-N-(ethoxycarbonyl)neamine (4), were prepared by random hydrolysis of the 5,6-O-ethoxyethylidene derivative (2), followed by chromatographic purification. Condensation of 4 and 2,3,5-tri-O-benzoyl-d-ribofuranosyl chloride led to 6-O-(β-d-ribofuranosyl)neamine (7). Analogous condensation of 4 with 2,3,4,6-tetra-O-acetyl-α-d-glucopyranosyl bromide or 2,3,4,6-tetra-O-acetyl-α-d-galactopyranosyl bromide afforded the corresponding 6-O-(d-hexopyranosyl)neamines.     

Flavonoid diversification in different leaf compartments of Primula auricula (Primulaceae)

Populations of Primula auricula L. subsp. auricula from Austrian Alps were studied for flavonoid composition of both farinose exudates and tissue of leaves. The leaf exudate yielded Primula-type flavones, such as unsubstituted flavone and its derivatives, while tissue flavonoids largely consisted of flavonol 3-O-glycosides, based upon kaempferol (3, 4) and isorhamnetin (5–7). Kaempferol 3-O-(2″-O-β-xylopyranosyl-[6″-O-β-xylopyranosyl]-β-glucopyranoside) (3) and isorhamnetin 3-O-(2″-O-β-xylopyranosyl-[6″-O-β-xylopyranosyl]-β-glucopyranoside) (6) are newly reported as natural compounds. Remarkably, two Primula type flavones were also detected in tissues, namely 3′-hydroxyflavone 3′-O-β-glucoside (1) and 3′,4′-dihydroxyflavone 4′-O-β-glucoside (2), of which (1) is reported here for the first time as natural product. All structures were unambiguously identified by NMR and MS data. Earlier reports on the occurrence of 7,2′-dihydroxyflavone 7-O-glucoside (macrophylloside) in this species could not be confirmed. This structure was now shown to correspond to 3′,4′-dihydroxyflavone 4′-O-glucoside (2) by comparison of NMR data. Observed exudate variations might be specific for geographically separated populations. The structural diversification between tissue and exudate flavonoids is assumed to be indicative for different ecological roles in planta.