Synthesis of O‐β‐D‐Glucopyranosides of 7‐Hydroxy‐3‐(imidazol‐2‐yl)‐4H‐chromen‐4‐ones

The 7‐hydroxy‐3‐formyl‐4H‐chromen‐4‐one 1 reacted with various cyclic 1,2‐dicarbonyl compounds in the presence of ammonium acetate to furnish 7‐hydroxy‐3‐([4,5‐fused] imidazol‐2‐yl)‐4H‐chromen‐4‐ones 2a–f, which on glucosylation with α‐acetobromoglucose affords 2,3,4,6‐tetra‐O‐acetyl‐β‐D‐glucopyranosyloxy‐3‐([4,5‐fused] imidazol‐2‐yl)‐4H‐chromen‐4‐ones 3a–f. 7‐O‐β‐D‐Glucopyranosyloxy‐3‐([4,5‐fused] imidazol‐2‐yl)‐4H‐chromen‐4‐ones 4a–f were prepared by deacetylation with anhydrous zinc acetate in absolute methanol. The structure of these new O‐β‐D‐glucosides was established on the basis of chemical, elemental, and spectral analysis. These compounds were evaluated for their in vitro biological activity.

     

An Efficient Synthesis of Derivatives of 2‐Acetamido‐4‐amino‐2,4,6‐trideoxy‐D‐galactopyranose

Abstract

Methyl 2‐acetamido‐4‐amino‐2,4,6‐trideoxy‐α‐D‐galactopyranoside (10) was synthesized from D‐glucosamine hydrochloride in eight steps in an overall yield of 31%. Key steps include the selective benzoylation at O‐3 of methyl 2‐acetamido‐2,6‐dideoxy‐α‐D‐glucopyranoside in 89% yield and the subsequent Mitsunobu reaction using diphenylphosphoryl azide as the azide source which proceeded in 92% yield. Di‐ and mono‐benzyloxycarbonyl derivatives of 10 were also prepared.     

Synthesis of Novel Anellated Pyranosides as Precursors of C‐Nucleoside Analogues Using Isopropyl 6‐O‐Acetyl‐3‐deoxy‐4‐S‐ethyl‐4‐thio‐α‐D‐threo‐hexopyranosid‐2‐ulose

Abstract

Isopropyl 6‐O‐acetyl‐3‐deoxy‐4‐S‐ethyl‐4‐thio‐α‐D‐threo‐hexopyranosid‐2‐ulose (3) was converted to the corresponding 3‐[bis(methylthio)methylene] derivative 4 with a push–pull activated C–C double bond. Treatment of 4 with hydrazine and methylhydrazine afforded the pyrano[3,4‐c]pyrazol‐5‐ylmethyl acetates 5a and 5b, respectively. Desulfurization of compound 4 with sodium boron hydride yielded the 3‐[(methylthio)methylene]hexopyranosid‐2‐ulose 7. Compound 7 was reacted with amines to furnish 3‐aminomethylene‐hexopyranosid‐2‐uloses 8, 9. Reaction of 7 with hydrazine hydrate, hydrazines, hydroxylamine, and benzamidine afforded the pyrazolo, isoxazalo, and pyrimido anellated pyranosides (10–13).     

Synthesis of Substituted 1‐\C\‐Phenyl‐D‐Tetritols and 1‐C‐(1H‐Pyrazol‐4‐yl)‐D‐tetritols by Ring Transformation of 2‐Formylglycals

Abstract

2‐Formylglycals 1a,b reacted with dialkyl 3‐oxoglutarates in the presence of base to furnish the 5‐[(1R,2R(S),3R)‐1,2,4‐tris(benzyloxy)‐3‐hydroxy‐butyl]‐2‐hydroxy‐isophthalic acid dialkyl esters 2a–d. Treatment of 1a,b with hydrazine derivatives afforded the substituted 1,2,4‐tri‐O‐benzyl‐1C‐(1H‐pyrazol‐4‐yl)‐D‐tetritols 5a–d. Deprotection of 5a,b was achieved with Pd/H₂ to yield the 1C‐(1‐methyl‐1H‐pyrazol‐4‐yl)‐D‐tetritols 6a,b.     

Bromination of 4‐Dichloromethyl‐4‐methylcyclohexa‐2,5‐dien‐1‐ones

Bromination of 4‐dichloromethyl‐4‐methylcyclohexa‐2,5‐dien‐1‐one and 4‐dichloromethyl‐3,4‐dimethylcyclohexa‐2,5‐dien‐1‐one has been studied. The reaction conditions required for the formation of mono‐, di‐, and tribrominated products have been optimized.     

Synthesis and study of 4‐(4′‐n‐alkoxybenzoyloxybenzoyl)‐4′′‐n‐butoxyanilides

Thirteen compounds with ester and amide linkages were synthesized and their mesogenic properties evaluated. Methyl to n‐propyl derivatives exhibit nematic phases, n‐butyl to n‐decyl derivatives exhibit smectic and nematic mesophases, whereas n‐dodecyl to n‐octadecyl derivatives exhibit only smectic phases. All the smectic homologues exhibit smectic C phases. Middle members of the homologous series exhibit polymorphism of smectic mesophase. A plot of transition temperatures versus number of carbon atoms in the alkoxy chain reveals an odd–even effect for nematic–isotropic transition temperatures. Nematic–isotropic and smectic–cholesteric thermal stabilities of the prepared compounds (series I) are higher compared to those of previously reported compounds, series A, B and C. The results indicate that a simple reversal of a central linkage has a dramatic effect on the appearance of smectic mesophase in a homologous series. The structures of the synthesized compounds were characterized using elemental analysis, thin‐layer chromatography and spectral data.     

Facile Synthesis of 2‐Alkylthio‐5,5‐dimethyl‐4H‐imidazol‐4‐ones

The isothiocyanate 3, obtained from aza‐Wittig reaction of iminophosphorane 2 with CS₂, reacts with phenylhydrazine to give thiosemicarbazide 4. Reactions of 4 with alkyl halides in the presence of K₂CO₃ directly provided 2‐alkylthio‐4H‐imidazol‐4‐ones 6 in good yields.     

A Novel,Convenient Synthesis of the 3‐O‐β‐D‐ and 4′‐O‐β‐D‐Glucopyranosides of trans‐Resveratrol

Abstract

trans‐Resveratrol‐3‐O‐β‐D‐glucupyranoside (trans‐piceid, 2) and trans‐resveratrol‐4′‐O‐β‐D‐glucupyranoside (trans‐resveratroloside 3) are the naturally occurring O‐glucoside conjugates of the polyphenolic stilbenoid trans‐resveratrol 1. Recently, attention has been drawn towards the interesting biological properties of the glucoside conjugates 2 and 3 as well as those of the aglycone 1. The fact that only limited quantities can be obtained by extraction from natural sources has prompted the development of novel syntheses of 2 and 3, based on a convergent Heck‐coupling strategy, which now conveniently allows for the preparation of multi‐milligram to gram quantities of each.     

Facile Synthesis of 2‐Alkylthio‐3‐alkyl‐5‐phenylmethylidene‐4H‐imidazol‐4‐ones

2‐Alkylthio‐3‐alkyl‐5‐phenylmethylidene‐4H‐imidazol‐4‐ones 6 were synthesized by N‐alkylation and S‐alkylation of 2‐thioxo‐5‐phenylmethylidene‐4‐imidazolidinone 5, which was obtained via cyclization of vinyl isothiocyanate 4 with excess ammonium hydroxide (28% NH₃ in water).     

Synthesis of 4‐Substituted‐ and 1,4‐Disubstituted‐4‐Hydroxypyrrolidin‐2‐ones

This report describes the synthesis of 4‐substituted‐ and 1,4‐disubstituted‐4‐hydroxypyrrolidin‐2‐ones by cyclization of intermediate γ‐aminoesters prepared from alkylbenzylamines, α‐bromoketones, and lithio ethyl acetate.     

Synthesis of an α‐Gal epitope α‐D‐Galp‐(1→3)‐β‐D‐Galp‐(1→4)‐β‐D‐Glcp NAc–lipid conjugate*

The synthesis of a neoglycoconjugate containing the Galili epitope trisaccharide connected to a spacer‐lipid entity is described. The α‐D‐Galp‐(1→3)‐β‐D‐Galp‐(1→4)‐β‐D‐GlcpNAc trisaccharide, equipped with a 3‐aminopropyl spacer, is efficiently assembled from easily accessible building blocks in a one‐pot procedure. Global deprotection of the trisaccharide and ensuing introduction of a bis(palmitamido)‐ propanamido moiety afforded title compound 1 as depicted in Scheme 1.     

Synthesis of 3‐Methoxyoxetane δ‐Amino Acids with D‐lyxo,D‐ribo,and D‐arabino Configurations

Starting from 1,2‐isopropylidene‐d‐xylose (1), 3‐methoxyoxetane δ‐amino acids with d‐lyxo, d‐ribo, and d‐arabino configurations were synthesized. The early introduction of an azide function at C‐5 of 1 shortened the synthetic pathway. Ring contraction of the intermediate d‐xylono‐1,4‐lactone 6 via triflation and treatment with base led to the corresponding 3‐methoxyoxetane δ‐amino ester with d‐lyxo configuration 7. The analogous procedure for d‐ribono‐1,4‐lactone 16 furnished a mixture of d‐ribo and d‐arabino esters 17 and 18. Hydrolysis of the methyl esters 7, 17, and 18 to their corresponding δ‐amino acids was successful with LiOH in THF, in contrast to that of their 3‐hydroxy analog 11.      

Synthesis and Antimicrobial Activity of 4‐Aryl‐5‐phenyl‐imino‐3‐(tetra‐O‐benzoyl‐β‐D‐glucopyranosylimino)‐1,2,4‐dithiazolidines (Hydrochlorides)

Abstract

Synthesis of 4‐aryl‐5‐phenylimino‐3‐(tetra‐O‐benzoyl‐β‐D‐glucopyranosylimino)‐1,2,4‐dithiazolidines (hydrochlorides) is described. These compounds were screened for their antibacterial and antifungal activity against Escherichia coli, Staphylococcus aureus, P. vulgaris, Pseudomonas, Bacillus, Salomonella sp., Aspergilus niger, and Fusarium. The identities of these new N‐glucosides have been established on the basis of usual chemical transformation IR, NMR, and mass spectral studies.     

A Common Sugar as Model for Many‐Sided Natural Product Modification. From D‐Fructose via D‐Tagatose to 2‐C‐Chlorodifluoro‐methylated D‐Arabinopyranos‐5‐ulose Derivatives

Abstract

Starting with 3,4‐O‐[(R)‐2,2,2‐trichloroethylidene]‐1,2‐O‐isopropylidene‐β‐D‐tagatopyranose 2 obtained from 1,2‐O‐isopropylidene‐β‐D‐fructopyranose 1 by a non‐classical one‐step acetalization with chloral/DCC, the fluoroalkylated glycosyl donors 15 and 17 were synthesised in 3–4 steps. By this sequence, one stereogenic center was inverted, one new chiral center was introduced, and one stereogenic center, for the time being eliminated, was later re‐introduced. The glycals 11 and 12, key intermediates of the synthesis sequence, were accessible from triflate precursors (e.g., 10) by treatment with DBU. Corresponding halogeno‐(6, 7), tosyl‐(5, 8), or mesyl‐(9) precursors were unsuitable. The stereoselective introduction of a chlorodifluoromethyl group was realised by dithionite‐mediated CF₂ClBr‐addition to the glycal double bond. Subsequently, either the chlorodifluoromethylated glycosyl bromide (13) or the corresponding pyranoses (14 and 16) were isolated. The latter were still acetylated to the 1‐O‐acetyl derivatives 15 and 17, respectively. An x‐ray analysis is given for the 5‐O‐tosylate 8.     

Organic Base‐Catalyzed Stereoselective Isomerizations of 4‐Hydroxy‐4‐phenyl‐but‐2‐ynoic Acid Methyl Ester to (E)‐ and (Z)‐4‐Oxo‐4‐phenyl‐but‐2‐enoic Acid Methyl Esters

We have developed a 1,4‐diazabicyclo[2.2.2]octane (DABCO)‐catalyzed isomerization of 4‐hydroxy‐4‐phenyl‐but‐2‐ynoic acid methyl ester to (E)‐4‐oxo‐4‐phenyl‐but‐2‐enoic acid methyl ester and an N,N‐diisopropylethylamine‐catalyzed isomerization of the same substrate to (Z)‐4‐oxo‐4‐phenyl‐but‐2‐enoic acid methyl ester.     

Microwave‐Assisted Elimination Reaction of trans‐4‐(4‐Fluorophenyl)‐3‐chloromethyl‐1‐methylpiperidine on Alumina

Abstract

trans‐4‐(4‐Fluorophenyl)‐3‐chloromethyl‐1‐methylpiperidine 3b was subjected to elimination reaction on alumina or KF‐alumina under solvent‐free conditions and microwave irradiation. Compared with the “classical” method of heating in the presence of an organic base, the microwave‐assisted methodology provided higher yields of 4‐(4‐fluorophenyl)‐3‐methylene‐1‐methylpiperidine 7b (65.5–71%) in considerably shorter reaction times (20–40 min). Furthermore, the exocyclic double bond in 7b underwent rearrangement to the endocyclic double bond to furnish compound 8. The effect of alumina and irradiation time on reaction conversion and the extent of isomerization was examined.     

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 and Structure of 2‐Hydroxy‐2‐Methyl‐1,3‐Bis‐(Methyl 3′,4′,6′‐Tri‐O‐Acetyl‐β‐D‐Glucopyranosid‐2‐yl)‐Imidazolidine‐4,5‐Dione

The title compound was synthesized starting from methyl 3,4,6‐tri‐O‐acetyl‐2‐acetamido‐2‐deoxy‐β‐D‐glucopyranoside, oxalyl chloride, and methyl 3,4,6‐tri‐O‐acetyl‐2‐amino‐2‐deoxy‐β‐D‐glucopyranoside. The crystal and molecular structure of the obtained imidazolidine‐4,5‐dione have been determined by X‐ray analysis as well as ¹H and ¹³C NMR spectroscopy.     

Catalytic Synthesis of D‐Glucosaminic Acid from D‐Glucosamine on Active Charcoal‐Supported Pd‐Bi Catalysts

D‐Glucosaminic acid (2‐amino‐2‐deoxy‐D‐gluconic acid), is a component of bacterial lipopolysaccharides, sweetener, condiments, and a chiral synthon. A catalytic oxidation of D‐glucosamine to D‐glucosaminic acid by molecular oxygen on active charcoal‐supported Pd‐Bi catalysts is described in good yield.