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C-2 Epimer Of D-glucose

Monosaccharides

Monosaccharides

MS are identified by the number of carbons present i.e.triose, tetrose, pentose, hexose etc., and by its reaction functional groupnamely aldose if functional group is aldehyde -CH=O, and ketose if functionalgroup is ketone or carbonyl -C=O. The smallest MS are trioses e.g. glyceraldehyde (aldotriose)and dihydroxyacetone (ketotriose). Glyceraldehyde has a chiral C so twostereoisomers are possible. All sugars are referred to these two isomersin order to classify the sugar D or L. In biological systems the D-isomerpredominates. As the number of carbons increase then the problem of stereoisomerismbecomes greater e.g. glucose is an aldohexose and contains 4 chiral C withpossibility of 16 isomers. The assignment of sugar to D or L series is determinedby examination of the furthest away chiral C from the aldehyde functionalgroup i.e. C5 (carbon 5) for comparison with D & L glyceraldehyde: inthis case OH is on RHS so this is D-glucose, L-glucose would be the mirrorimage of this. D-galactose and D-mannose are also stereoisomers of D-glucosei.e. 2 of the 16 possible and these two found in living organisms. D-glucoseand D-galactose also referred to as epimers because the two MS only differin the configuration of a single carbon C4. D-glucose and D-mannose arealso epimers and the difference is at C2. However D-galactose and D-mannoseare not epimers because they differ at C2 and C4. MS with 5 or more C will not stay in the linear from whendissolved in solution. In solution they tend to form cyclic ring structuresas C1 and C5 form an oxygen bridge - ring structure called a hemiacetal.The most common in nature are ring structures formed by 5C and 6C sugarsreferred to as furanose and pyranose respectively. So hemiacetal is thename of the bridge bond and furanose refers to a 5C ring an Continue reading >>

4.7: R And S Assignments In Compounds With Two Or More Stereogenic Centers

4.7: R And S Assignments In Compounds With Two Or More Stereogenic Centers

4.7: R and S Assignments in Compounds with Two or More Stereogenic Centers The Chinese shrub Ma Huang (Ephedra vulgaris) contains two physiologically active compounds ephedrine and pseudoephedrine. Both compounds are stereoisomers of 2-methylamino-1-phenyl-1-propanol, and both are optically active, one being levorotatory and the other dextrorotatory. Since the properties of these compounds (see below) are significantly different, they cannot be enantiomers. How, then, are we to classify these isomers and others like them? Ephedrine: m.p. 35 - 40 C, []D = 41, moderate water solubility [this isomer may be referred to as ()-ephedrine] Pseudoephedrine: m.p. 119 C, []D = +52, relatively insoluble in water [this isomer may be referred to as (+)-pseudoephedrine] Since these two compounds are optically active, each must have an enantiomer. Although these missing stereoisomers were not present in the natural source, they have been prepared synthetically and have the expected identical physical properties and opposite-sign specific rotations with those listed above. The structural formula of 2-methylamino-1-phenylpropanol has two stereogenic carbons (#1 & #2). Each may assume an R or S configuration, so there are four stereoisomeric combinations possible. These are shown in the following illustration, together with the assignments that have been made on the basis of chemical interconversions We turn our attention next to molecules which have more than one stereocenter. We will start with a common four-carbon sugar called D-erythrose. A note on sugar nomenclature: biochemists use a special system to refer to the stereochemistry of sugar molecules, employing names of historical origin in addition to the designators 'D' and 'L'. You will learn about this system if you take a bioche Continue reading >>

Carbohydrates - Chemistry Encyclopedia - Structure, Reaction, Proteins, Molecule, Aldoses, Ketoses, Monosaccharide Derivatives

Carbohydrates - Chemistry Encyclopedia - Structure, Reaction, Proteins, Molecule, Aldoses, Ketoses, Monosaccharide Derivatives

Carbohydrates are the most abundant natural organic compounds on Earth. The term "carbohydrate" derives from their general formula of C n (H 2 O) n , first determined in the nineteenth century, and indicates that these compounds are hydrates of carbon. Carbohydrates are more specifically defined as polyhydroxy aldehydes or ketones and the products derived from them. Carbohydrates are synthesized via photosynthesis by plants, algae, and some bacteria. Animals feeding on these organisms then use the energy stored in these compounds. Energy storage is not the only function of carbohydrates. They have a variety of functions in living organisms, including their contribution to the structure of cell walls and their vital role in communication at the site of cell membranes. Carbohydrates form part of the backbone of RNA and DNA molecules, and they are also found linked to proteins and lipids as glycoproteins and glycolipids. The three basic groups of carbohydrates based on size are: monosaccharides , oligosaccharides, and polysaccharides (saccharide from the Greek sakcharon , or "sugar"). The oligosaccharides and polysaccharides are composed of a few and many monosaccharides, respectively. Monosaccharides have two major groups: the aldoses and the ketoses. The simplest of the aldoses is glyceraldehyde, which is a triose, or three-carbon sugar. Glyceraldehyde has one chiral carbon and therefore two stereoisomers, designated D and L. In nature, only D sugars occur in abundance. Other aldoses can be derived from glyceraldehyde via insertion of additional hydroxy carbons between the carbonyl carbon and the molecule's other carbons. In this way, tetroses, pentoses, and hexoses are formed. Although glyceraldehyde and the tetroses can occur only as simple linear structures, Figure 1 Continue reading >>

Dietary D-psicose, A C-3 Epimer Of D-fructose, Suppresses The Activity Of Hepatic Lipogenic Enzymes In Rats.

Dietary D-psicose, A C-3 Epimer Of D-fructose, Suppresses The Activity Of Hepatic Lipogenic Enzymes In Rats.

Dietary D-psicose, a C-3 epimer of D-fructose, suppresses the activity of hepatic lipogenic enzymes in rats. Faculty of Agriculture, Kagawa University, Kita-gun, Japan. [email protected] D-Psicose (D-ribo-2-hexulose), a C-3 epimer of D-fructose, is present in small quantities in commercial carbohydrate complexes or agricultural products. Wistar male rats were fed experimental diets which consisted of 5% D-psicose, cellulose, D-fructose or D-glucose for 28 days. Abdominal adipose tissue weight was significantly lower (P < 0.05) in rats fed the D-psicose diet than in rats fed a D-fructose and D-glucose diets, even though the four dietary groups were offered the same amount throughout the experimental period. Fatty acid synthase and glucose 6-phosphate dehydrogenase activities in the liver were significantly lower (P < 0.05) in rats fed the D-psicose diet than in rats fed the D-fructose and D-glucose diets. However, lipoprotein lipase activities in the heart, soleus muscle and perirenal adipose tissue were the same. These results suggest that a supplement of D-psicose in the diet suppresses hepatic lipogenic enzyme activities. The lower abdominal fat accumulation in rats fed a D-psicose diet might result from lower lipogenesis in the liver. Continue reading >>

Chapter 14 Practice

Chapter 14 Practice

D-Allose is the C-3 epimer of D-glucose. Write its structure in anopen-chain form, in a Haworth projection (a beta-pyranose), and in a chairform. Draw D-ribose in its pyranose form, in both a Haworth projection andin a chair form. Draw the disaccharide that would result from linking D-glucose fromits alpha-1 position to the C-4 position of D-galactose (which is the C-4epimer of D-glucose). Identify the sugars above as reducing or non-reducing sugars. Write the steps involved in converting open-chain D-ribose into methylbeta-D-ribofuranoside. Use methanol with acid catalysis. * Emil Fischer identifies the configuration of glucose * This sequence of experiments illustrates the logic behind "howdo we know" the structures of compounds. In the last 95 years, ourexperiments have become more complex and sophisticated but the art of creatinginformative experiments and the logic applied in their interpretation remainas valid as ever. Try to follow the award-winning logic. a) Glucose was known to be an aldohexose. b) All stereochemistry was related to the configuration at C-5 (Fischer assumed the C-5 OH was to the right - D - which was correct) The Kiliani-Fischer synthesis was developed to convert an aldose toa mixture of the two epimers that have one more carbon: 1) Arabinose, an aldopentose, leads to glucose and mannose. (Conclusion: glucose and mannose are C-2 epimers, with their C-3,4,5 likearabinose) 2) Arabinose is oxidized by HNO3 to give an optically active aldaricacid. (Conclusion: if C-5 is right, C-3 must be left - both right would have givenan optically inactive (meso) aldaric acid) 3) The aldaric acids from glucose and mannose are both optically active. (Conclusion: C-4 must be right - if C-4 were left, one of the two epimerswould have given an optically inactive ( Continue reading >>

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An Error Occurred Setting Your User Cookie

An Error Occurred Setting Your User Cookie This site uses cookies to improve performance. If your browser does not accept cookies, you cannot view this site. There are many reasons why a cookie could not be set correctly. Below are the most common reasons: You have cookies disabled in your browser. You need to reset your browser to accept cookies or to ask you if you want to accept cookies. Your browser asks you whether you want to accept cookies and you declined. To accept cookies from this site, use the Back button and accept the cookie. Your browser does not support cookies. Try a different browser if you suspect this. The date on your computer is in the past. If your computer's clock shows a date before 1 Jan 1970, the browser will automatically forget the cookie. To fix this, set the correct time and date on your computer. You have installed an application that monitors or blocks cookies from being set. You must disable the application while logging in or check with your system administrator. This site uses cookies to improve performance by remembering that you are logged in when you go from page to page. To provide access without cookies would require the site to create a new session for every page you visit, which slows the system down to an unacceptable level. This site stores nothing other than an automatically generated session ID in the cookie; no other information is captured. In general, only the information that you provide, or the choices you make while visiting a web site, can be stored in a cookie. For example, the site cannot determine your email name unless you choose to type it. Allowing a website to create a cookie does not give that or any other site access to the rest of your computer, and only the site that created the cookie can read it. Continue reading >>

Mocycles

Mocycles

The Chemical Education Journal (CEJ), Vol. 9, No. 1 (Serial No. 16). The date of issue: , 2005./Registration No. 9-/Received November 1, 2005. Monosaccharide Cycles: A Method to Determine the General Stereochemical Relationships of both D and L Monosaccharides. Department of Chemistry, Kenyon College, Gambier, OH 43022 Abstract . Using a cyclic representation of both D and L monosaccharides, named monosaccharide cycles, a method for determining the stereochemical relationships of all (both D and L) monosaccharides is proposed. It would be a very useful tool for teaching Organic, Bioorganic, and Carbohydrate Chemistry and Biochemistry. Keywords : Organic Chemistry, Biochemistry, Carbohydrates, Nomenclature, Stereochemistry. Carbohydrates, proteins, and nucleic acids constitute the three most important biopolymers in living systems. Natural amino acids, the building units of proteins, differ only by their side chains and almost all of them have the L-configuration. Nucleic acids are phosphodiester-linked riboses or deoxyriboses to which one of four types of bases are attached. In contrast, the monosaccharides, the building units of carbohydrates, have multiple stereocenters. The presence of these multiple stereocenters contribute to the rich structural diversity of carbohydrates, enabling them to serve as molecular (cellular) barcodes. For example, studies have demonstrated that oligosaccharides are involved in a number of recognition events such as cell adhesion, metastasis, fertilization and embryonic development, amongst others.[1,2] In organic and carbohydrate chemistry, the monosaccharides are typically represented in a chart form [3-5] and their naming follows the IUPAC-IUBMB nomenclature.[6] Understanding the nomenclature and the stereochemical relationships betwe Continue reading >>

Epimer - Wikipedia

Epimer - Wikipedia

This article's factual accuracy is disputed . Relevant discussion may be found on the talk page . Please help to ensure that disputed statements are reliably sourced . In stereochemistry , an epimer is one of a pair of stereoisomers . The two isomers differ in configuration at only one stereogenic center . All other stereocenters in the molecules, if any, are the same in each. Doxorubicin and epirubicin are two epimers that are used as drugs. The sugars glucose and galactose are epimers. In glucose, the -OH group on the first carbon is in the axial position, the direction opposite the -OH group on carbon C-4. In galactose, the -OH group is oriented in the same direction, the equatorial position. [1] In cyclical compounds like these, the -OH group on C-1 may lie in opposite directions as well. This structural difference distinguishes two anomers . The two molecules pictured are both epimers and anomers (as indicated by the and designation). -mannopyranose are epimers because they differ only in the stereochemistry at the C-2 position. The hydroxyl group in -D-glucopyranose is axial (up from the "plane" of the ring), while in -D-mannopyranose the C-2 hydroxyl group is equatorial (in the "plane" of the ring). These two molecules are epimers but, because not mirror images of each other, are not enantiomers . (Enantiomers have the same name but differ in classification.) They are also not sugar anomers , since the wrong carbon is involved in the stereochemistry. Continue reading >>

L-arabinose Binding, Isomerization, And Epimerization By D-xylose Isomerase: X-ray/neutron Crystallographic And Molecular Simulation Study - Sciencedirect

L-arabinose Binding, Isomerization, And Epimerization By D-xylose Isomerase: X-ray/neutron Crystallographic And Molecular Simulation Study - Sciencedirect

Volume 22, Issue 9 , 2 September 2014, Pages 1287-1300 L-Arabinose Binding, Isomerization, and Epimerization by D-Xylose Isomerase: X-Ray/Neutron Crystallographic and Molecular Simulation Study Joint X-ray/neutron structures of D-xylose isomerase with L-arabinose Structures and QM/MM reveal L-arabinose conformation is 5S1 in the active site MD simulations suggest mutations to improve enzyme affinity to L-arabinose Isomerization between L-ribulose and L-ribose may proceed by cis-ene-diol pathway D-xylose isomerase (XI) is capable of sugar isomerization and slow conversion of some monosaccharides into their C2-epimers. We present X-ray and neutron crystallographic studies to locate H and D atoms during the respective isomerization and epimerization of L-arabinose to L-ribulose and L-ribose, respectively. Neutron structures in complex with cyclic and linear L-arabinose have demonstrated that the mechanism of ring-opening is the same as for the reaction with D-xylose. Structural evidence andQM/MM calculations show that in the reactive Michaelis complex L-arabinose is distorted to the high-energy 5S1 conformation; this may explain the apparent high KM for this sugar. MD-FEP simulations indicatethat amino acid substitutions in a hydrophobic pocket near C5 of L-arabinose can enhance sugar binding. L-ribulose and L-ribose were found in furanose forms when bound to XI. We propose that these complexes containing Ni2+ cofactors are Michaelis-like and the isomerization between these two sugars proceeds via a cis-ene-diol mechanism. Continue reading >>

Epimers And Epimerization (molecular Biology)

Epimers And Epimerization (molecular Biology)

Epimers and Epimerization (Molecular Biology) Epimers are diastereomers that are related by the inversion of configuration at a single chiral center (1). This definition extends the original meaning of epimer, which was used to identify sugars that differed in configuration at C2 (2). This definition intentionally excludes enantiomers, such as D- and L-alanine, since they are not diastereomers. It also excludes diastereomers that are related by the inversion of more than a single chiral center. Thus, D-glucose and D-mannose are epimers, as are D-glucose and D-galactose. D-mannose and D-galactose are not epimers, however, because they are related by inversion at two chiral centers, C2 and C4 (Fig. 1) Figure 1. Stereochemical drawings of glucose, mannose, and galactose, with their four chiral carbons. The configurations at C2 and C4 are labeled and distinguish these three sugars. Glucose is an epimer of both mannose and galactose because they differ by the configuration of a single chiral center. Mannose and galactose have different configurations at both C2 and C4 and are not epimers. The chemical conversion of one epimer to another is called epimerization. If this interconversion is catalyzed by an enzyme, the enzyme is an epimerase. As an example, UDP-glucose-4-epimerase catalyzes the epimerization of the C4 carbon of glucose. In the reaction, UDP-glucose is epimerized to UDP-galactose. When the inversion of configuration occurs to interconvert enantiomers instead of diastereomers, the reaction is a racemization. Continue reading >>

Biochem 153a: Week 4 Discussion Handout Answers

Biochem 153a: Week 4 Discussion Handout Answers

note: We reviewed all of these structures in discussion, plus they are readily available to you in the compendium,so you'll only see comments where structures need to be drawn. 1) All biological sugars are D enantiomers. This means that humans have enzymes that process D sugars (i.e. glucose),and our planet Earth generally has presented us with D-sugars for our consumption. If you somehow got ahold of a potato from some other planet in the universe that produces L sugars and had the nerve to take a bite, you'd probably getpretty sick with indigestion, having all those L-glucoses in your stomach. 2) Glucose-remember that right-left-right transfers to down-up-down when you go from the straight chain, Fischerprojection to the ring, Haworth form. 4) "oside" means that the anomeric carbon is an acetal. "ose" means that the anomeric carbon is a hemiacetal. 1) A glycosidic bond originates from an anomeric carbon and is bonded to the oxygen of the hydroxyl group on somethingelse, which can be another monosaccharide (ie glucose, fructose, etc), or a serine in a polypeptide (resulting in aglycoprotein), or an alcohol (like methanol), or glycerol (resulting in a glycolipid). It's a C to O bond, not an area, but one bond. 2) The reducing end refers to a Tollen's test result, which is experimentally derived, but can be predicted based on the configuration of the anomeric carbon. A sugar solution is reacted with Tollen's reagent, which contains silver nitrate, an oxidizing agent. Sugars with free anomeric carbon atoms are reasonably good at reducing oxidizing agents. So, ifthe anomeric carbon is free, that is called the reducing end (RE) of the sugar. If not (ie engaged in a covalentglycosidic bond), it is called non-reducing (NRE). One caveat is that this test was based on amount o Continue reading >>

Organic Chemistry - Are Glucose And Galactose Cis-trans Isomers Of Each Other? - Chemistry Stack Exchange

Organic Chemistry - Are Glucose And Galactose Cis-trans Isomers Of Each Other? - Chemistry Stack Exchange

Are glucose and galactose cis-trans isomers of each other? Glucose and galactose are diastereomers of each other. However, is it correct to say that they are cis-trans isomers of each other? Does it make a difference with regard to terminology if glucose and galactose are in cyclic form i.e. are glucopyranose and galactopyranose cis-trans-isomers of each other? And is it correct to say that glucopyranose has $2^5-1=31$ cis-trans isomers? I would also appreciate some references to verify the correct use of terminology in this situation. NOTE: I have edited this question to clarify that I'm interested in the cyclic form as well. Since the question was revised, I have revised the answer as well to include more information: Glucose and galactose are not cis isomers, but diastereomers called epimers, Two sugars that differ only in the configuration around one carbon atom are called epimers; D-glucose and D-mannose, which differ only in the stereochemistry at C-2, are epimers, as are D-glucose and D-galactose (which differ at C-4): In other words they are nonsuperimposable, nonmirror-image stereoisomers. The explanation below gives some insight on what forms of isomerism such sugars exhibit: The predominant form of stereo-isomerism in such sugars as monosaccharides is optical isomerism. Simple substances which show optical isomerism exist as two isomers known as enantiomers. A solution of one enantiomer rotates the plane of polarisation in a clockwise direction. This enantiomer is known as the (+) form.A solution of the other enantiomer rotates the plane of polarisation in an anti-clockwise direction. This enantiomer is known as the (-) form. For monosaccharides with two or more asymmetric carbons, the prefix D or L refers to the configuration of the highest numbered asymmet Continue reading >>

Carbohydrates

Carbohydrates

Carbohydrates are the most abundant class of organic compounds found in living organisms. They originate as products of photosynthesis, an endothermic reductive condensation of carbon dioxide requiring light energy and the pigment chlorophyll. As noted here, the formulas of many carbohydrates can be written as carbon hydrates, Cn(H2O)n, hence their name. The carbohydrates are a major source of metabolic energy, both for plants and for animals that depend on plants for food. Aside from the sugars and starches that meet this vital nutritional role, carbohydrates also serve as a structural material (cellulose), a component of the energy transport compound ATP , recognition sites on cell surfaces, and one of three essential components of DNA and RNA. Carbohydrates are called saccharides or, if they are relatively small, sugars. Several classifications of carbohydrates have proven useful, and are outlined in the following table. sugars having an aldehyde function or an acetal equivalent. sugars having a ketone function or an acetal equivalent. sugars oxidized by Tollens' reagent (or Benedict's or Fehling's reagents). sugars not oxidized by Tollens' or other reagents. Carbohydrates have been given non-systematic names, although the suffix ose is generally used. The most common carbohydrate is glucose (C6H12O6). Applying the terms defined above, glucose is a monosaccharide, an aldohexose (note that the function and size classifications are combined in one word) and a reducing sugar. The general structure of glucose and many other aldohexoses was established by simple chemical reactions. The following diagram illustrates the kind of evidence considered, although some of the reagents shown here are different from those used by the original scientists. Hot hydriodic acid (HI) wa Continue reading >>

Structural Biochemistry/carbohydrates/monosaccharides

Structural Biochemistry/carbohydrates/monosaccharides

Structural Biochemistry/Carbohydrates/Monosaccharides Monosaccharides are the simplest form of carbohydrates and may be subcategorized as aldoses or ketoses . The sugar is an aldose if it contains an aldehyde functional group. A ketose signifies that the sugar contains a ketone functional group. Monosaccharides may be further classified based on the number of carbon atoms in the backbone, which can be designated with the prefixes tri-(3), tetr-(4), pent-(5), hex-(6), hept-(7), etc. in the name of the sugar. Monosaccharides are often represented by a Fischer Projection, a shorthand notation particularly useful for showing stereochemistry in straight chained organic compounds. The L and D confirmations represent the absolute configuration of the asymmetric carbon farthest away from the ketone or aldehyde group on the monosaccharide. On the Fischer projection, if the farthest hydroxyl(-OH) group is on the right, then it is classified as D sugar, if the hydroxyl group is on the left, then it is a L sugar. Enantiomers, Diastereoisomers(anomerism), and Epimers[ edit ] Example of Diastereomers. The areas marked blue indicate the differing stereogenic centers. Example of an Enantiomer. The blue indicates the D-isomer and the red indicates the L-isomer Due to the fact that carbohydrates contain multiple stereocenters, many isomers are possible including enantiomers, diastereoisomers, and epimers. Two carbohydrates are said to be enantiomers if they are nonsuperimposable mirror images of one another. An example of an enantiomer is the D and L isomers of glucose, as shown by the figure to the right. A second type of isomer seen in carbohydrates are diastereoisomers. Carbohydrates are classified as diastereomers if their chiral carbons are connected to the exactly the same substra Continue reading >>

Epimer, Epimers Of Glucose | Chemistry@tutorvista.com

Epimer, Epimers Of Glucose | [email protected]

Carbohydrates act as the most important source of energy for our body and one of the main types of nutrients. In living systems carbohydrates mainly convert to glucose which is also called as blood sugar and uses this sugar as energy source. The excess of glucose stores in the form of starch (in plants) and glycogen (in animal) for when it is needed. Depending on their chemical structures, carbohydrates can be simple or complex compounds. Simple carbohydrates include sugars found naturally in foods like dairy products, vegetables and fruits. While the complex carbohydrates include starchy vegetables, cereals, legumes and whole grain breads. They are organic molecules with the general formula of CH2O and constitute only 1 - 2 percent of cell mass as they provide the raw fuel for cellular energy production. They mainly classified according to molecular size and solubility. In general, the smaller carbohydrates are more soluble than the larger ones. For example, monosaccharides like glucose, fructose, galactose, deoxyribose, and ribose are soluble in water as they contain a single unit of sugar. Out of these carbohydrates, glucose is a hexose sugar in our blood, and fructose is mainly present in sweetens fruits, however galactose is found in milk and it is a isomer of glucose. Sugar with five carbon atoms are called as pentose sugar like deoxyribose and ribose present in nucleic acids. Monosaccharides are bonded together through glycosidic linkage to form disaccharides like sucrose, maltose and lactose. Sucrose composed of glucose and fructose unit while Lactose formed by the combination of glucose and galactose units. Similarly two units of glucose bonded together to form maltose sugar. Polysaccharides are composed of 10-1000 units of monosaccharides bonded through glyco Continue reading >>

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