Carbohydrate e sters

1. Carbohydrate esters Derivatives of carbohydrates with one or more hydroxyl groups substituted with an acid moiety. According to the degree and mode of substitution, they can be partial, full or mixed esters. The most important carbohydrate esters are: - with carboxylic acids: acetates (O-acetyl derivatives) –OCOMe (-OAc) benzoates (O-benzoyl derivatives) –OCOPh (-OBz) - with sulfonic acids: methanesulfonates (mesylates, O-methanesulfonyl derivatives, O-mesyl derivatives) -OSO2Me (-OMs) toluene-4-sulfonates (tosylates, O-toluene-4-sulfonyl derivatives, O-tosylderivatives)-OSO2C6H4Me-4 (-OTs) -with mineral acids: phosphates -OPO3H2 sulfates -OSO3H nitrates -ONO2 borates (non anomerc) halogenides

2. Carbohydrate esters • They are prepared by reaction of a sacharide with chlorides (benzoates, sulfonates, carbonates, phosphates, sulfates) or anhydrides of acids (acetates, sulfates), usually in basic medium (most often in pyridine), eventually directly with an acid (nitrates, borates).

3. Preparation of acetates 100 ºC, 1 h 100 ºC, 1 h

4. Reactions of acetates • Zemplén deacetylation – O-deacetylation of acetates of sacharides by trans-esterification in anhydrous methanol in the presence of a catalytic amount of sodium methoxide.

5. Migration of esters • Some partial esters of sacharides (e. g., acetates, benzoates, phosphates) undergo both basic and acid catalyzed migration of the ester group. In general, the direction of this intramolecular arrangement is from a secondary towards a free primary hydroxylgroup. Thus, e. g., 1,2,3,4-tetra-O-acetyl--D-glucopyranose in 0,001 N sodium hydroxide is transformed to 1,2,3,6-tetra acetate.

6. Migration of esters 81 % from α-acetate,51 % from β-acetate In practical synthesis, such acyl migration is observed quite often.For example,when treated with iodomethane in presence of silver oxide, 1,3,4,6-tetra-O-acetyl-α- or -β-D-glucopyranoseyields metyl2,3,4,6-tetra-O-acetyl-β-D-glucopyranoside.

7. Sulfonates The very great importance of sulfonate esters in carbohydrate chemistry stems from excellent ‘leaving properties’ of sulfonyloxy group in nucleophilic displacement reactions, i.e. from the propensity of these derivatives to react by alkyl-oxygen fission (route a) rather than by sulfur-oxygen fission (route b). Most other esters react by process equivalent to route (b) (e.g. see acetates (carboxylates) in the Zemplen deacetylation), and cosequently do not offer a means of carrying out chemical operations at the carbon atoms of sugar chains. Carboxylates

8. Displacement of sulfonates None 3-benzoate

9. Reaktivitu pri substitúcii sulfonátov významne ovplyvňuje stereochemické usporiadanie ostatných substituentov na sacharidovom skelete. Podobné prejavy závislosti reaktivity na stereochemickom usporiadaní sa pravidelne pozorujú aj pri iných derivátoch sacharidov. Preto pri posudzovaní reaktivity akejkoľvek funkčnej skupiny v sacharidoch a ich derivátoch ako relatívne zložitých molekulách je nevyhnutné chápať molekulu sacharidu vždy ako celok a nestačí sa obmedziť na príslušnú funkčnú skupinu.

10. Artificial fats sucrose glycerine olestra fats and oils R = stearoyl, palmitoyl, oleyl Substitution of at least six hydroxygroups of sucrose by acyloxy moieties of higher fatty acids R gave rise to a non-metabolizable substitute of natural fats. Olestra was approved by the Food and Drug Administration for use as a food additive in 1996, and was commercialized by Procter & Gamble Co.The presence of sucrose esters with fatty acids in foods is declared by symbol E 473.

11. „Edible“ detergents • Esters of fatty acids and sucrose are usedas non toxic, biologicallydegradable detergents (degree of substitution 1-3). • Many non-ionogenic surface-active substancesbased onsorbitol (D-glucitol) are used infood industry as emulsifiers of water-in-oil type and as antifoaming agents.They are obtained by esterificationofsorbitol withfatty acids.

12. Artificial sweeteners • Cukraloseis a chlorinated sucrosederivative, with a D-galactopyranosyl unit instead of the D-glucopyranosyl unit,and containing three chlorine atoms instead of hydroxy groups. This derivativeis 600-timessweeter than sucrose. • Cukraloseis not metabolized. It is fairlysoluble and 60-timesmore stablein acidic media than sucrose. Used in some countries as noncaloric sweetener, most often under commercial name Splenda.In EU it is known as E955. sucralose two conformations ofsucrose withrelevant intramolecular hydrogen bonds

13. Artificial sweeteners aspartám (dipeptid L-asparagínu a L-fenylalanínu) alitám (dipeptid L-asparagínu a D-alanínu) sacharín acesulfám K cyklamát (Na+ alebo Ca2+)

14. Artificial sweeteners Relativesweetness*of major nutričných sladidiel ------------------------------------------------------------------------------- Sladidlo Relativesweetness ------------------------------------------------------------------------------- Alitam 200 000-290 000 Cukralose 55 000-75 000 Sacharin 30 000 Aspartam 18 000-20 000 Acesulfam K 15 000-20 000 Cyklamate 3 000 -------------------------------------------------------------------------------*Sucrose = 100

15. http://en.wikipedia.org/wiki/Steviol_glycoside The steviol glycosides are responsible for the sweet taste of the leaves of the stevia plant (Stevia rebaudiana Bertoni). These compounds range in sweetness from 40 to 300 times sweeter than sucrose.[1] They are heat-stable, pH-stable, and do not ferment.[2] They also do not induce a glycemic response when ingested, making them attractive as natural sweeteners to diabetics and others on carbohydrate-controlled diets. Stevioside D-glucose D-glucose Steviol D-glucose

16. The diterpene known as Steviol is the aglycone of stevia's sweet glycosides, which are constructed by replacing steviol's carboxyl hydrogenatom (at the bottom of the figure) with glucose to form an ester, and replacing the hydroxyl hydrogen (at the top of the figure in the infobox) with combinations of glucose and rhamnose. The two primary compounds, stevioside and rebaudioside A, use only glucose: Stevioside has two linked glucose molecules at the hydroxyl site, whereas rebaudioside A has three, with the middle glucose of the triplet connected to the central steviol structure. In terms of weight fraction, the four major steviol glycosides found in the stevia plant tissue are: 5–10% stevioside (250–300X of sugar) 2–4% rebaudioside A — most sweet (350–450X of sugar) and least bitter 1–2% rebaudioside C ½–1% dulcoside A. Rebaudioside B, D, and E may also be present in minute quantities; however, it is suspected that rebaudioside B is a byproduct of the isolation technique.[2] The two majority compounds stevioside and rebaudioside, primarily responsible for the sweet taste of stevia leaves, were first isolated by two French chemists in 1931.[3] http://en.wikipedia.org/wiki/Steviol_glycoside

17. http://delibo.sk/images/product/708.jpg http://www.jakbydlet.cz/images/L%C3%A9%C4%8Divky/Stevia.jpg http://members.chello.sk/fytomodelovanie/stevia%20v%20crepniku2.jpg

18. E Numbers E numbers are codes for chemicals which can be used as food additives for use within the European Union and Switzerland (the "E" stands for "Europe"). • E100–E199 (colours) • E200–E299 (preservatives) • E300–E399 (antioxidants, acidity regulators) • E400–E499 (thickeners, stabilizers, emulsifiers) • E500–E599 (acidity regulators, anti-caking agents) • E600–E699 (flavour enhancers) • E700–E799 (antibiotics) • E900–E999 (glazing agents and sweeteners) • E1000–E1599 (additional chemicals)