Die Cardenolide und Pregnan-Glykoside der Wurzeln von Asclepias lilacina WEIMARCK. I. Isolierungen Glykoside und Aglykone, 290. Mitteilung

The dried roots of Asclepias lilacina contain ca. 14% glykosides, in which both cardenolides and ester glycosides of pregnane derivatives are present, the latter predominating. Uzarigenin, coroglaucigenin, and their corresponding glycosides ascleposide and frugoside, resp., were shown to be present; of these four, uzarigenin was isolated in crystalline form. The ester glycosides, some of which could be isolated in a crystalline state, are predominantly composed of the aglycones 20-O-acetyl-12-O-benzoyl-sarcostin and 12,20-di-O-benzoyl-sarcostin, besides which esters of desacetyl-metaplexigenin, lineolon, and dihydrosarcostin are also present. These aglycones are mostly attached to various trisaccharides which are composed of at least two 2-deoxy-sugar residues. Mild acid hydrolysis gave, besides the genins, 7 sugars, namely cymarose, oleandrose, digitoxose, 3-O-methyl-6-deoxy-D-allose (U3), as well as 3 unknown sugars U1, U2 and U5 which are probably disaccharides. U1 and U2 were isolated in crystalline form; they are isomeric and have been named asclepobiose and lilacinobiose; they are probably composed of units similar to those in the isomeric pachybiose.     

Determination of 2-deoxyaldoses and their natural glycosides with the aid of xanthydrol

Summary The molecular extinction coefficients in the xanthydrol reaction of 2-deoxyaldoses and their cardenolide glycosides have been measured. The absorption indices vary within wide limits according to the structure of the sugars. The 2,6-dideoxyaldoses have a considerably higher coefficient than the 2-deoxyaldoses. Disaccharides in which 2,6-dideoxyaldohexoses are attached to the D-glucose show a comparatively low optical density. The glycosides reflect the properties of the sugars that they contain.A rough method of determining the amount of pregnane glycosides in plants has been developed.Institute of the Chemistry of Plant Substances, Academy of Sciences of the Uzbek SSR. Translated from Khimiya Prirodnykh Soedinenii, No. 5, pp. 641–646, September–October, 1973.     

8-Hydroxyquinoline as a building block for artificial receptors: binding preferences in the recognition of glycopyranosides

8-Hydroxyquinoline-based receptors 1-3, containing a trisubstituted triethylbenzene core, were prepared and their binding properties towards glycosides were evaluated. (1)H NMR and fluorescence titrations as well as binding studies in two-phase systems, such as dissolution of solid carbohydrates in apolar media and phase transfer of sugars from aqueous into organic solvents, revealed β- vs.α-anomer binding preferences in the recognition of glycosides. Compared to the previously described three-armed aminopyridine-based receptor, compounds 1 and 2 showed significantly increased affinity to β-galactoside. Receptor 2, incorporating two 8-hydroxyquinoline units, was shown to be the most effective receptor for β-galactoside. Compound 3, bearing one 8-hydroxyquinoline group, was found to be a highly effective receptor for β-glucoside and shown to be a more powerful receptor than the quinoline-based compound 4, indicating an important role of the quinoline hydroxy group in the complex formation.     

The pregnane derivatives of the seeds from Dregea abyssinica (Hochst.) K. Schum. (Asclepiadacea). I. Isolation

The seeds of Dregea abyssinica (HOCHST .) K. Schum. are very rich in glycosides. These consist of a complicated mixture of ester glycosides, cardenolides are absent. All these glycosides are derived from only the two known pregnane derivatives drevogenin P and Drevogenin D. In the glycosides the latter are esterified with different acids (acetic, isovaleric, α-hydroxyisovaleric and tiglic acid) and glycosidically linked to different 2-deoxy-sugars which in part carry 3-O-methyl-6-deoxy-D-allose and terminal D-glucose. After mild acidic hydrolysis 5 crystalline sugars and 6 crystalline aglycones could be isolated. The sugars were identified as D-cymarose, asclepobiose, pachybiose, drebyssobiose and «sugar T» (formerly found in Dregea volubilis). The following aglycones were obtained: drevogenin A, drevogenin B, and four new compounds called drebyssogenin F, G, J and K. The latter was a mixture of two components (K1 and K2). From the original mixture four genuine glycosides could be isolated (the drebyssosides 1, 2, 3 and 4). Of these the drebyssosides 1 and 3 were obtained crystalline, drebyssoside 2 in amorphous but pure form and drebyssoside 4 as a mixture of mainly two closely related components. The probable structures of the new substances (drebyssobiose, sugar T, the four drebyssogenins and the four drebyssosides) are reported in the following publication.     

Protecting group free glycosylation: one-pot stereocontrolled access to 1,2-trans glycosides and (1→6)-linked disaccharides of 2-acetamido sugars

Unprotected 2-acetamido sugars may be directly converted into their oxazolines using 2-chloro-1,3-dimethylimidazolinium chloride (DMC), and a suitable base, in aqueous solution. Freeze drying and acid catalysed reaction with an alcohol as solvent produces the corresponding 1,2-trans-glycosides in good yield. Alternatively, dissolution in an aprotic solvent system and acidic activation in the presence of an excess of an unprotected glycoside as a glycosyl acceptor, results in the stereoselective formation of the corresponding 1,2-trans linked disaccharides without any protecting group manipulations. Reactions using aryl glycosides as acceptors are completely regioselective, producing only the (1→6)-linked disaccharides.

Un-protected 2-acetamido sugars are stereoselectively converted into 1,2-trans glycosides and (1→6)-linked disaccharides without any protecting groups. Reaction proceeds via intermediate oxazolines which react with acceptors under acid catalysis.     

Rapid resolution of carbohydrate isomers by electrospray ionization ambient pressure ion mobility spectrometry-time-of-flight mass spectrometry (ESI-APIMS-TOFMS)

Carbohydrates are an extremely complex group of isomeric molecules that have been difficult to analyze in the gas phase by mass spectrometry because (1) precursor ions and product ions to successive stages of MS(n) are frequently mixtures of isomers, and (2) detailed information about the anomeric configuration and location of specific stereochemical variants of monosaccharides within larger molecules has not been possible to obtain in a general way. Herein, it is demonstrated that gas-phase analyses by direct combination of electrospray ionization, ambient pressure ion mobility spectrometry, and time-of-flight mass spectrometry (ESI-APIMS-TOFMS) provides sufficient resolution to separate different anomeric methyl glycosides and to separate different stereoisomeric methyl glycosides having the same anomeric configuration. Reducing sugars were typically resolved into more than one peak, which might represent separation of cyclic species having different anomeric configurations and/or ring forms. The extent of separation, both with methyl glycosides and reducing sugars, was significantly affected by the nature of the drift gas and by the nature of an adducting metal ion or ion complex. The study demonstrated that ESI-APIMS-TOFMS is a rapid and effective analytical technique for the separation of isomeric methyl glycosides and simple sugars, and can be used to differentiate glycosides having different anomeric configurations.     

Synthesis of racemic sugars and their analogs from dihydropyrans (review)

New methods for the synthesis of glycosides of racemic sugars and some of their derivatives from various dihydropyran compounds are discussed. The problems involved in the preparation of 2-alkoxydihydropyrans with multiple bonds in various positions of the ring and problems of the stereospecificity of the epoxidation and hydroxylation of substituted dihydropyrans are examined. The stereospecificity and regiospecificity of opening of the epoxide ring of a large number of epoxytetrahydropyrans were studied in detail. It is shown that dihydropyran compounds are convenient substrates for the preparation of various racemic deoxy sugars, amino deoxy sugars, and their derivatives.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 867–880, July, 1977. 26, 1976.     

Kaempferol glycosides in the flowers of carnation and their contribution to the creamy white flower color

Three flavonol glycosides were isolated from the flowers of carnation cultivars 'White Wink' and 'Honey Moon'. They were identified from their UV, MS, 1H and 13C NMR spectra as kaempferol 3-O-neohesperidoside, kaempferol 3-O-sophoroside and kaempferol 3-O-glucosyl-(1 --> 2)-[rhamnosyl-(1 --> 6)-glucoside]. Referring to previous reports, flavonols occurring in carnation flowers are characterized as kaempferol 3-O-glucosides with additional sugars binding at the 2 and/or 6-positions of the glucose. The kaempferol glycoside contents of a nearly pure white flower and some creamy white flower lines were compared. Although the major glycoside was different in each line, the total kaempferol contents of the creamy white lines were from 5.9 to 20.9 times higher than the pure white line. Thus, in carnations, kaempferol glycosides surely contribute to the creamy tone of white flowers.     

A Simplified,One-Pot Preparation of Acetobromosugars from Reducing Sugars

ABSTRACT

Acetobromoglycoses continue to be important as glycosyl donors in the synthesis of simple glycosides as well as complex oligosaccharides. From reducing sugars they are usually prepared via their peracetates in two steps. In the first step, sugars are converted to their peracetates using pyridine and acetic anhydride^1,2 and the acetates are then converted in a second step to acetobromosugars using a solution of hydrogen bromide in glacial acetic acid(HBr/HOAc).² Although not in use very often Redemann and Niemann³ as well as Lemieux⁴ have described one-pot methods for the preparation of acetobromoglucose wherein the reducing sugar is first treated with acetic anhydride in the presence of sulfuric acid³ or perchloric acid⁴ respectively to afford the peracetate. Direct conversion of the peracetate to its 1-bromo-derivative, in yields ranging from 80-87%, was then achieved by either treating the solution of the peracetate with gaseous HBr³ or with bromine in the presence of red phosphorus.⁴ In another approach to a one-pot method Humoller⁵ prepared tri-O-acetyl-β-L-arabinopyranosyl bromide in 40% yield by passing anhydrous HBr gas through a suspension of L-arabinose in acetic anhydride. By an essentially similar method Dale⁶ obtained acetobromosugars in yields ranging from 26-77% depending upon the sugar. Because acetobromosugars are the compounds most frequently used for synthesizing numerous other sugar derivatives, we thought it would be worthwhile to report our recent observation that acetic anhydride and HBr/HOAc can be used with advantage for the preparation of acetobromosugars.     

New water soluble glycosides of 11-keto-β-boswellic acid: A paradigm

Though several glycosides of various triterpenes are known, but surprisingly no boswellic acid glycosides are reported so far. With a view to make water soluble boswellic acids, prepared glycosides of 11-keto boswellic acid for the first time. Naturally occurring boswellic acids which are anti-inflammatory agents are lipophylic in nature and thus, become a limiting factor in terms of their bioavailability. Among boswellic acids, 11-keto-β-boswellic acid is found to exhibit superior biological activity and hence successfully prepared its glucosyl and maltosyl derivatives viz., 11-keto-β-boswellic acid-24-O-β-D-glucopyranoside (9) and 11-keto-β-boswellic acid-24-O-α-D-glucopyranosyl-(1 → 4)-β-D-glucopyranoside (15) which are water soluble. Both these compounds are soluble in water to the extent of 10% (w/w) which is very significant.     

Synthesis and mycobacterial growth inhibition activities of bivalent and monovalent arabinofuranoside containing alkyl glycosides

Arabinofuranosides constitute one of the important components of cell wall structures of mycobacteria. With this importance of arabinofuranosides in mind, alkyl glycosides bearing arabinofuranoside trisaccharides were prepared, wherein the sugars were presented either in the monovalent or bivalent forms. Following the synthesis, the monovalent and bivalent alkyl glycosides were tested for their activities in a mycobacterial growth assay. The growth of the mycobacterial strain M. smegmatis was assessed in the presence of the alkyl glycosides and it was realized that the alkyl glycosides acted as inhibitors of the mycobacterial growth. The inhibition of the growth, caused by the above alkyl glycosides, was not observed for the arabinofuranose trisaccharide alone, without the alkyl groups, and for an alkyl glycoside bearing maltose as the sugar component.     

The alkaline hydrolysis of flavonoid glycosides

Conclusions 1. The alkaline hydrolysis of flavonoid glycosides has been studied.2. In an alkaline medium 3-glycosides, C-glycosides, and biosides having 1, 2 bonds between the sugars are stable.3. The difference in the stabilities of the glycosides to alkalis can be used in studying flavonoid O-diglycosides, O-biosides with different positions of the bond, O,C-diglycosides, and O,C-biosides.Khimiya Prirodnykh Soedinenii, Vol. 5, No. 5, pp. 366–369, 1969     

1-bromo-1-lithioethene: a practical reagent for the efficient preparation of 2-bromo-1-alken-3-ols

A reliable preparative-scale synthesis of 1-bromo-1-lithioethene is reported. This reagent undergoes clean 1,2-addition with a range of aldehydes and ketones at -105 degrees C to afford the corresponding 2-bromo-1-alken-3-ols in moderate to excellent yield. Efficient diastereoselective addition to alpha-siloxy and alpha-methylcyclohexanones, as well as protected 3-keto furanose sugars, is achieved in the presence of 10 mol % CeBr(3). The resulting bromoallylic alcohol adducts have considerable potential as synthetic building blocks. [reaction: see text]     

若干天然糖苷类的快原子轰击质谱及快原子轰击碰撞活化质量分析离子动能谱研究

糖苷类化合物因为极性大和热不稳定而难以用通常的电子轰击电离质谱进行结构测定. 我们用FAB-MS和FAB-CA-MIKES对这类化合物进行了结构研究, 不仅获得了准确的分子量和苷元碎片, 还获得了糖的序列以及糖本身的裂解途径等重要结构信息.     

Identification of common glycosyl groups of flavonoid O‐glycosides by serial mass spectrometry of sodiated species

Flavonoid O‐glycosides are a ubiquitous and important group of plant natural products in which a wide variety of sugars are O‐linked to an aglycone. Determining the identity of the sugars, and the manner in which they are linked, by mass spectrometry alone is challenging. To improve the identification of common O‐linked di‐ and trisaccharides when analysing mixtures of flavonoid O‐glycosides by liquid chromatography/mass spectrometry (LC/MS), the fragmentation of electrosprayed sodium adducts in an ion trap mass spectrometer was investigated. The sodium adducts [M + Na]⁺ of kaempferol 3‐O‐glycosides generated sodiated glycosyl groups by the neutral loss of kaempferol. The product ion spectra of these sodiated glycosyl groups differed between four isomeric kaempferol 3‐O‐rhamnosylhexosides and four isomeric kaempferol 3‐O‐glucosylhexosides in which the primary hexose was either glucose or galactose and bore the terminal glucose or rhamnose at either C‐2 or C‐6. Fragmentation of sodiated glycosyl groups from linear O‐triglucosides and branched O‐glucosyl‐(1 → 2)‐[rhamnosyl‐(1 → 6)]‐hexosides produced sodiated disaccharide residues, and the product ion spectra of these ions assisted the identification of the complete sugar. The product ion spectra of the sodiated glycosyl groups were consistent among flavonoid O‐glycosides differing in the position at which the sugar was O‐linked to the aglycone, and the nature of the aglycone. The abundance of sodiated species was enhanced by application of a pre‐trap collision voltage, without the need to dope with salt, allowing automated LC/MS methods to be used to identify the glycosyl groups of common flavonoid O‐glycosides, such as rutinosides, robinobiosides, neohesperidosides, gentiobiosides and sophorosides. Copyright © 2011 John Wiley & Sons, Ltd.     

Protecting‐Group‐Free One‐Pot Synthesis of Glycoconjugates Directly from Reducing Sugars

The conversion of sugars into glycomimetics typically involves multiple protecting‐group manipulations. The development of methodology allowing the direct aqueous conversion of free sugars into glycosides, and mimics of oligosaccharides and glycoconjugates in a high‐yielding and stereoselective process is highly desirable. The combined use of 2‐azido‐1,3‐dimethylimidazolinium hexafluorophosphate and the Cu‐catalyzed Huisgen cycloaddition allowed the synthesis of a range of glycoconjugates in a one‐step reaction directly from reducing sugars under aqueous conditions. The reaction, which is completely stereoselective, may be applied to the convergent synthesis of triazole‐linked glycosides, oligosaccharides, and glycopeptides. The procedure provides a method for the one‐pot aqueous ligation of oligosaccharides and peptides bearing alkyne side chains.     

Evaluation of glycosylation and malonylation patterns in flavonoid glycosides during LC/MS/MS metabolite profiling

Flavonoid conjugates constitute several classes of plant phenolic secondary metabolites including many isomeric compounds differing in the hydroxylation pattern and substitution of their rings with different groups such as alkyls, acyls or sugars. These compounds occur in plant tissues mainly as glycosides and in many cases it is necessary to have reliable and detailed information concerning the structure of these natural products. Our results were obtained using leaf extracts of Arabidopsis thaliana and Lupinus angustifolius in which different glycosides of flavones, flavonols and isoflavones are present. Analysis of collision-induced dissociation (CID)/MS/MS spectra of protonated [M + H](+), sodiated [M + Na](+) or deprotonated [M - H](-) molecules recorded during HPLC runs may bring needed information in this respect. However, registration of mass spectra of [M + Na](+) ions with a good efficiency is possible only after post-column addition of a sodium acetate solution to the LC column eluate. The retention of sodium cation on the saccharidic parts of the molecule is observed after the CID fragmentation. In many cases, the location of this cation on the glycan attached to C-3 hydroxyl group of flavonol led to assignment of its structure. Additionally, the determination of the structure of the aglycone and of the sequence of the glycan part was made possible through the CID data obtained from the [M + H](+) and [M - H](-) ions. CID spectra show a different order of sugar elimination from hydroxyl groups at C-3 and C-7 in flavonol glycosides isolated from A. thaliana leaves and give sufficient information to discriminate flavonoid O-diglycosides from flavonoid di-O-glycosides.     

Stereoselective Synthesis of α‐Linked 2‐Deoxy Glycosides Enabled by Visible‐Light‐Mediated Reductive Deiodination

2‐Deoxy sugars and their derivatives occur abundantly in many pharmaceutically important natural products. However, the construction of specific 2‐deoxy‐glycosidic bonds remains as a challenge. Herein, we report an efficient way to prepare 2‐deoxy‐α‐glycosides by glycosylation of 2‐iodo‐glycosyl acetate and subsequent visible‐light‐mediated tin‐free reductive deiodination. We have successfully applied the postglycosylational‐deiodination strategy in the synthesis of more than 30 mono‐, di‐, tri‐, tetra‐ and pentadeoxysaccharides with excellent stereoselectivity and efficiency. This method has also been applied to the synthesis of a 2‐deoxy‐tetrasaccharide containing four α‐linkages.     

Copper-catalyzed Pummerer type reaction of α-thio aryl/heteroarylacetates: Synthesis of aryl/heteroaryl α-keto esters

A copper catalyzed Pummerer type reaction of α-thio aryl/heteroarylacetates is described for the first time. This transformation represents a new route to synthesize α-keto esters, which are important intermediates for pharmaceuticals and organic synthesis. The reaction proceeds via in situ generation of a thionium ion that undergoes hydrolysis to furnish α-keto esters in synthetically viable yields (up to 82%).     

A divergent strategy for constructing a sugar library containing 2,6-dideoxy sugars and uncommon sugars with 4-substitution

A practical strategy has been developed for delivering 2,6-dideoxy sugars and uncommon sugars with 4-substitution. This strategy employed Ferrier rearrangement reaction and BF₃·OEt₂-induced peroxidation to construct key intermediates 2,3-unsaturated glycosides and α,β-unsaturated lactones from peracetyl rhamnal. After further derivatization, four uncommon sugars with 4-substitution and eight uncommon sugar units with 3,4-disubstitution were successfully synthesized.