Synthesis of a Tetrasaccharide Related to the Repeating Unit of the Antigen from Shigella dysenteriae Type 9 in the Form of Its 2‐(Trimethylsilyl)ethyl Glycoside

Abstract

Starting from D‐mannose, D‐galactose and D‐glucosamine hydrochloride, two disaccharide blocks were synthesized. Schmidt's inverse addition technique for trichloroacetimidate was utilized for the construction of a disaccharide with a β‐mannosidic linkage in good yield. The two disaccharides in the appropriate form were then allowed to react in the presence of N‐iodosuccinimide (NIS) and trifluoromethanesulfonic acid (TfOH) to give the tetrasaccharide derivative from which removal of protecting groups gave the desired tetrasaccharide in the form of its 2‐(trimethylsilyl)ethyl glycoside.     

Synthesis of the Trisaccharide Repeating Unit of the O‐Antigen Related to the Enterohemorrhagic Escherichia coli Type O26:H

l‐Fucose was converted to the 2‐azido‐2‐deoxy‐l‐fucose derivative, which together with the monosaccharide synthons prepared from l‐rhamnose and d‐glucosamine hydrochloride were utilized for the synthesis of the p‐ethoxyphenyl glycoside of the trisaccharide repeating unit of the antigen from enterohemorrhagic Escherichia coli type O26:H.     

Synthesis of the C‐Glycoside of Methyl α‐d‐Altropyranosyl‐(1→4)‐α‐d‐glucopyranoside

The C‐glycoside of methyl α‐d‐altropyranosyl‐(1→4)‐α‐d‐glucopyranoside 2 was prepared in a convergent fashion, from readily available precursors, 4‐O‐tert‐butyldiphenylsilyl‐1,2‐O‐isopropylidene‐d‐erythro‐S‐phenyl monothiohemiacetal 13 (five steps from D‐ribose) and the known acid, methyl 2,3,6‐tri‐O‐benzyl‐4‐C‐(carboxymethyl)‐4‐deoxy‐α‐d‐glucopyranoside 17 (seven steps from methyl α‐d‐glucopyranoside). The key reactions in the synthesis are the oxocarbenium ion cyclization of thioacetal‐enol ether 19 to a C1 substituted glycal 20, and the stereoselective hydroboration of 20 to the α‐C‐altroside 21.     

Asymmetric Synthesis of (R)‐(−)‐Rhododendrol,the Aglycone of the Hepatoprotective Agent Rhododendrin

Abstract

Starting from 2,3‐O‐isopropylidene‐D‐glyceraldehyde (3) as chiral material, (R)‐(?)‐rhododendrol 2, the aglycone of the naturally occurring rhododendrin 1 was synthesized.     

Amino Acids as a Chiral Pool: Synthesis of (S)‐and (R)‐2‐N‐Carbomethoxy‐5‐aminoindane from (S)‐ and (R)‐Phenylalanines

Enantioselective syntheses of (R)‐and (S)‐2‐N‐carbomethoxy‐5‐aminoindanes from (R)‐ and (S)‐phenylalanines, respectively, are described. A Friedel–Crafts reaction employing N‐carbomethoxy phenylalanine leads to chiral 2‐N‐carbomethoxy‐1‐indanone, which is diastereoselectively reduced to 1‐hydroxy‐2‐N‐carbomethoxyindane. After protection of the hydroxyl group, a regioselective nitration gives a 6‐nitroindane intermediate, which upon hydrogenation affords (R)‐or (S)‐2‐N‐carbomethoxy‐5‐aminoindane.     

Versatile Approach for the Asymmetric Synthesis of (R)‐ and (S)‐Massoialactones

A general synthetic approach to both enantiomers, (R)‐ and (S)‐massoialactones, has been devised from commercially available (S)‐butane‐1,2,4‐triol.     

An Advanced Intermediate for the Synthesis of (±)‐Pumiliotoxin C and Its Analogues

Abstract

Compound 1 as a versatile intermediate for the synthesis of (±)‐pumiliotoxin C and its analogues was prepared from commercially available cyclohexanone. The key step in the synthesis was the construction of octahydroquinoline ring by a stereoselective aminocyclization.     

Synthesis of (R)‐Japonilure and (4R,9Z)‐9‐Octadecen‐4‐olide,Pheromones of the Japanese Beetle and Currant Stem Girdler

Asymmetric total synthesis of the sex pheromones of Japanese beetle and currant stem girdler, (R)‐japonilure (1) and (4R,9Z)‐9‐octadecen‐4‐olide (2), has been achieved.     

Studies Towards the Synthesis of the β‐D‐Xyl‐(1 → 3)‐L‐ara Disaccharide Moiety of OSW‐1 from Ornithogalum saundersiae

Abstract

The OSW‐1 disaccharide having 2‐O‐p‐methoxybenzoyl‐β‐D‐xylopyranosyl‐(1 → 3)‐L‐arabinopyranoside structure was obtained as the benzylated 4‐O‐acetyl derivative 19. Also, the 4,2′‐di‐O‐acetate 18 was synthesized by a short synthetic approach. The arabinose acceptor 15 was obtained in a three step‐one pot sequence from easily available benzyl β‐L‐arabinopyranoside.     

Isolation and Structure Characterization of a (4‐O‐Methyl‐d‐glucurono)‐d‐xylan from the Skin of Opuntia ficus‐indica Prickly Pear Fruits

A slightly water soluble (4‐O‐methyl‐d‐glucurono)‐d‐xylan was isolated from the skin of Opuntia ficus‐indica (OFI) fruits by alkaline extraction, followed by ethanol precipitation and ion‐exchange chromatography. The structure of this xylan was determined by sugar determination coupled with a ¹H and ¹³C NMR spectroscopy analysis. The xylan consisted of a linear (1→4)‐β‐d‐xylopyranosyl backbone decorated with 4‐O‐methyl‐α‐d‐glucopyranosyluronic acid groups linked to the C‐2 of the xylopyranosyl residues, in the ratio of one uronic acid for six neutral sugar units.     

Nitroimidazoles,Part 1. An Unexpected Reactivity During the Cyclization of 3‐(4‐Amino‐1‐benzyl‐2‐ethyl‐1H‐imidazol‐5‐ylsulphanyl)‐propionic Acid Methyl Ester

Nucleophilic substitution of the 5‐bromo group in 1 by methyl 3‐mercaptopropionate gave the 5‐alkyl‐mercapto derivative 2. Reduction of 2 with H₂/Pd led to the amine 3, meanwhile reduction with Fe/HOAc afforded the 5‐acetamido derivative 4 and not the cyclized derivative 1,3,8‐triaza‐azulen‐7‐one 6, as expected. Treatment of 3 with NaOMe/MeOH furnished the racemic mixture 5a and 5b via an unexpected reactivity.     

Study on the Total Synthesis of 3-Oxo-9β-Acetoxyilicic Acid─The Synthesis of 9β-Acetoxy-3(4),11(13)-Dien-5αH,7αH-12-Eudesmanoic Acid Methyl Ester

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Synthesis of C‐Nucleoside Analogues Starting from 1‐(Methyl 3‐O‐benzyl‐4,6‐O‐benzylidene‐2‐deoxy‐α‐D‐altropyranosid‐2‐yl)‐4‐phenyl‐but‐3‐yn‐2‐one

Abstract

1‐(Methyl 3‐O‐benzyl‐4,6‐O‐benzylidene‐2‐deoxy‐α‐D‐altropyranosid‐2‐yl)‐4‐phenyl‐but‐3‐yn‐2‐one (4) was synthesized by the reaction of (methyl 3‐O‐benzyl‐4,6‐O‐benzylidene‐2‐deoxy‐α‐D‐altropyranosid‐2‐yl)ethanal (2) with lithium phenylethynide and following oxidation. Compound 4 and hydrazine hydrate provided the 3(5)‐(methyl 3‐O‐benzyl‐4,6‐O‐benzylidene‐2‐deoxy‐α‐D‐altropyranosid‐2‐yl‐methyl)‐5(3)‐phenyl‐1H‐pyrazole (5). The reactions of 4 with amidinium salts and a S‐methyl‐isothiouronium salt, respectively, furnished the pyrimidine C‐nucleoside analogues 6a–6c. Treatment of 4 with 2‐aminobenzimidazole afforded 2‐(methyl 3‐O‐benzyl‐4,6‐O‐benzylidene‐2‐deoxy‐α‐D‐altropyranosid‐2‐ylmethyl)‐4‐phenyl‐benzo [4,5]imidazo[1,2‐a]pyrimidine (7a). Compound 4 and sodium azide yielded 2‐(methyl 3‐O‐benzyl‐4,6‐O‐benzylidene‐2‐deoxy‐α‐D‐altropyranosid‐2‐yl)‐1‐[5(4)‐phenyl‐1H(2H)‐1,2,3‐triazole‐4(5)‐yl]ethanone (8).     

Synthesis of the Polymer of 1 {3-O[(R)-1 (L-Alanyl-D-Isoglutamyl Carbonyl) Ethyl]-α-D-Glucopyranos-6-O-Carbonycarbonyl}Ethylene

Abstract

The polymer of 1- 3-O [(R)1-(L-alanyl-D-isoglutamyl carbonyl)ethyl] α-D-glucopyranos-6-O-carbonyl ethylene was synthesized as a acryloyl type polymer by fixing the D-glucose analog (GADP) of N-acetylmuramyl-L-alanyl-D-isoglutamine (MDP), which is the minimum required structure responsible for the immunoadjuvant activity of bacterial cell-wall peptidoglycan. N- [2-(1,2-O-Isopropylidene-6-O-acryloyl-α-D-glucofuranos-3-Oyl)-(R)-propionyl] -L-alanyl-D-isoglutamine benzyl ester (6) was prepared as a key monomer in the synthesis. The homopolymerization of 6 and the copolymerization of 6 with hydrophobic acryloyl monomers were carried out in benzene at 60°C by using 2,2′-azobisisobutyronitrile as a radical initiator to give homopolymer 7 and copolymer 10, respectively. Removal of isopropylidene and benzyl protecting groups from 7, 10 and 8, 11 was carried out by acid treatment with trifluoroacetic acid/water (6:1 v/v) and by catalytic hydrogenolysis with palladium carbon, respectively, to afford the homopolymer 9 and the copolymer 12.     

Synthesis of the Potassium Channel Opener (3S,4R)‐3,4‐Dihydro‐4‐(2,3‐dihydro‐2‐methyl‐3‐oxo‐pyridazin‐6‐Yl)oxy‐3‐hydroxy‐6‐(3‐hydroxyphenyl)sulphonyl‐2,2,3‐trimethyl‐2H‐benzo[b]pyran

The preparation of the potassium channel opener (3S,4R)‐3,4‐dihydro‐4‐(2,3‐dihydro‐2‐methyl‐3‐oxo‐pyridazin‐6‐yl)oxy‐3‐hydroxy‐6‐(3‐hydroxyphenyl)sulphonyl‐2,2,3‐trimethyl‐2H‐benzo[b]pyran (1) as a single enantiomer is reported. Considerable improvements have been implemented with respect to the original synthesis that allow for the preparation of multigram quantities of the final target compound. The optimized synthesis consists of a six‐step linear sequence whose key step is an asymmetric epoxidation protocol through the use of Jacobsen's (S,S)‐(+)‐N,N′‐bis(3,5‐di‐tert‐butylsalicylidene)‐1,2‐cyclohexanediaminomanganese(III) chloride catalyst.     

Synthesis of chiral 2-(2′-pyrrolidinyl)pyridines from (S)- and (R)-proline: potential ligands of the neuronal nicotinic acetylcholine receptors

A new strategy for a straightforward synthesis of novel optically active nicotine analogues starting from (S)- and (R)-proline is reported utilizing as the key steps the inverse electron demand Diels–Alder reaction of, hitherto unknown, chiral 5-(2′-pyrrolidinyl)-1,2,4-triazines (S)- and (R)-16. These serve as appropriate precursors for the preparation of different, highly enantiomerically enriched 2-(2′-pyrrolidinyl)pyridines, modifications of natural (−)-nornicotine and (−)-nicotine and potential ligands of the neuronal nicotinic acetylcholine receptors. The multistep syntheses proceed under mild conditions, with good overall yields and with stereochemical integrity of the original stereogenic centers.     

Synthesis of (2R,3S)-isobutyl phenylisoserinate,the Taxol® side chain,from ethyl benzoylacetate

Reduction of ethyl 2-chloro-3-phenyl-3-oxopropionate with borohydride affords predominately the syn-chlorohydrin. Resolution of this ester with the lipase MAP-10 gives (2S,3R)-2-chloro-3-hydroxypropionic acid which after esterification with MeOH/HCl is converted to the cis-epoxide with potassium carbonate and DMF. Aminolysis of the epoxide with aqueous ammonia results in ring opening and amide formation. The amide is converted to an ester upon treatment with isobutyl alcohol and HCl(g) at 100°C. Neutralization then affords the Taxol^® side chain as the free amine.     

Synthesis and High-Field NMR of α-D-Arabinofuranosyl-(1→6)-2-AcetamidO-2-Deoxy-O-D-Glucopyranosyl-(1→3)-6-Deoxy-L-Talose,the Repeating Unit of an O-Specific Lipopolysaccharide from Pseudomonas Maltophilia N.C.I.B. 9204

Abstract

Starting from L-rhamnose, benzyl 2,4-di-O-benzyl-6-deoxy-α-L-talopyranoside (7) was prepared by hydrogenolysis of a dioxolane-type benzylidene acetal and used as the aglycon to prepare 2-acetamido-2-deoxy-6-D-glucopyranosyl-(1–3)-6-deoxy-L-talose (13) and the title trisacchafide (20). Due to fast interconvirsion between the α-, β- -pyranose/furanose forms at the reducing end of the molecule in aqueous solutions, the di- and trisaccharides occur as mixtures of four isomers all in significant concentration. By two-dimensional (20) methods, the proton (400) and carbon (100 MHz) NMR spectra of the individual tri-saccharide isomers were completely assigned and interpreted in terms of stereochemistry of the 6-deoxy-L-talose residue.     

Synthesis of the Four Configurational Isomers of N-Benzoyl-2, 3, 6-Trtdeoxy-3-C-Methyl-3-Amino-L-Hexose from the (2S, 3R)-Diol Obtained from α-Methylcinnamaldehyde by Fermentation with Baker'S Yeast

Abstract

The erythro and threo chiral C₅ methyl ketones (4) and (5), prepared from the (2S, 3R)-methyl diel (1b), were converted into the phenylsulfenimines (6) and (7), which, in turn, on reaction with allyl-magnesiutn bromide, yielded after acid hydrolysis and benzoylation, the diastereoisomeric C₈-N-aminodiol derivatives (9) and (11), with threo stereochemistry relative to positions 4 and 5. Ozonolysis of (9) and (11) yielded the l-arabino and l-xylo 3-O-methyl branched aminodeoxysugar derivatives (13) and (15), respectively. Using diallylzinc as the reagent, the diastereoisomeric erythro products (8) and (10) were obtained. The latter materials gave the l-ribo-and l-lyxo-(lL-vancosamine) derivatives (12) and (14) upon oxonolysis. The ¹H and ¹³C NMR spectra of the four isomeric aminodeoxysugar derivatives (12)—(15) were discussed.     

Rapid Access for the Synthesis of 1‐N‐Methyl‐spiro[2.3′]oxindole‐spiro[3.7″] (3″‐Aryl)‐5″‐methyl‐3″,3a″,4″,5″,6″,7″‐hexahydro‐2H‐pyrazolo[4,3‐c]pyridine‐4‐aryl‐pyrrolidines Through Sequential 1,3‐Dipolar Cycloaddition and Annulation

The 1,3‐dipolar cycloaddition of an azomethine ylide, generated from isatin and sarcosine by a decarboxylative route with various p‐substituted 3,5 bis(aryl methylidene)N‐methyl‐4‐piperidinones in refluxing methanol, proceeded regioselectively to give novel dispiroheterocycles. The product on subsequent annulation with hydrazine hydrate afforded 1‐N‐methyl‐spiro[2.3′]oxindole‐spiro[3.7″](3″‐aryl)‐5″‐methyl‐3″,3a″,4″,5″,6″,7″‐hexahydro‐2H‐pyrazolo[4,3‐c]pyridine‐4‐aryl‐pyrrolidines in good yield.