Esters in nature

Fatty acids occur mainly as esters in natural fats and oils but do occur in the unesterified form as free fatty acids, a transport form found in the plasma. Fatty acids that occur in natural fats are usually straight-chain derivatives containing an even number of carbon atoms. The chain may be saturated (containing no double bonds) or unsaturated (containing one or more double bonds). 

N. A. Sorensen Studies Related to Naturally Occurring Acetylene Compounds. IX. The Occurrence of Methyl dec-8-cis-en-4 6-diynoate (= a,/9-Dihydro-Matricaria Ester) and 2-cis 8-trans-Matricaria Ester in Nature. Acta Chem. Scand. 6, 883 (1952). 

A further important group of derivatives is that of amino acids activated by phosphoric acid or its esters. In nature, phosphorylation processes play an important activating role in peptide and protein synthesis. 

Phthalate esters, particularly, di-2-ethylhexyl phthalate (DEHP), are widely used as plasticizers. The total annual U.S. production of phthalate esters was over h00,000 tons in 1970 (1). Many of the applications of phthalate esters such as in construction, home furnishings, the automobile industry, etc. make it likely that they reach the aquatic environment. Since the initial report of the presence of phthalate esters in natural waters and fish in the United States by Mayer and coworkers (2), there have been reports of these chemicals in fish in Canada (3, t) and in Japan (5). The presence of phthalate esters in the ocean waters off the United States and in Gulf of Mexico biota has also been noted (6. ... 

A colleague of yours who investigates the fate of benzene sulfonates and benzene sulfonate esters in natural waters is interested in the stability of methyl-3,4-dichlorobenzene sulfonate (MDCBS) in aqueous solution. Because he has not read Chapter 13 of Environmental Organic Chemistry he asks you to help him to estimate the hydrolysis half-life of this compound in water at 25 °C and at 5°C. In the literature you find rate constants for the neutral hydrolysis of some substituted methyl benzene sulfonates at... 

Acetyl euenfytne A (usually abbreviated m etyl CoA> is the inod common thiol ester in nature. Acetyl CoA is a much more complex molecule than acetyl chloride or acetic anhydride, yet it serves exactly the same pur< pose as thene simpler reagents. Nature uses acetyl CoA as a reactive acyV atiog agent in nucleophilic acyl stilntitution reactions. 

MondeUo, L. Zappia, G. Bonaccorsi, I. Dugo, G. McNair, H.M. Fast GC for the analysis of natural matrices. PreUminary note The determination of fatty acid methyl esters in natural fats. J. Microcolunm September 2000, 12, 41-47. 

A typical research example includes the synthesis of a K -channel blocker intermediate (Fig. 7.10). Here, an aminotransferase is used to replace a keto group by an amino function to yield the desired intermediate [20]. Other potential applications include the biosynthesis of flavouring esters. In nature such compoimds are often formed by a specific acyl CoA transferase. For practical purposes, however, the alternative, less complicated route, using lipases and esterases in their synthetic mode, seems more appropriate. 

The structures of lipids are quite varied triacylglycerols (fats and oils), waxes, phospholipids, sphingolipids, steroids, eicosanoids, fat soluble vitamins, and pigments. Some lipids are simple in structure while others are more complex. Among these molecules are those which are esters in nature and therefore saponifiable in aqueous base. Others are nonsaponifiable. Many are completely nonpolar while others are amphipathic, that is, they have a polar/nonpolar nature. 

Esters in Nature Waxes, Fats, Oils, and Lipids CHAPTER 20... 

ESTERS IN NATURE WAXES, FATS, OILS, AND LIPIDS... 

The fatty acids occur in nature chiefly as glycerides see fats), which constitute the most important part of the fats and oils, and as esters of other alcohols, the waxes. The naturally occurring fatty acids are mostly the normal straight-chain acids with an even number of carbon atoms. 

Other polymers, such as poly methacrylates, have been studied, as well as esters of naturally occurring polysaccharides. References can be found in the literature cited in the list of further reading. 

Inspired by the many hydrolytically-active metallo enzymes encountered in nature, extensive studies have been performed on so-called metallo micelles. These investigations usually focus on mixed micelles of a common surfactant together with a special chelating surfactant that exhibits a high affinity for transition-metal ions. These aggregates can have remarkable catalytic effects on the hydrolysis of activated carboxylic acid esters, phosphate esters and amides. In these reactions the exact role of the metal ion is not clear and may vary from one system to another. However, there are strong indications that the major function of the metal ion is the coordination of hydroxide anion in the Stem region of the micelle where it is in the proximity of the micelle-bound substrate. The first report of catalysis of a hydrolysis reaction by me tall omi cell es stems from 1978. In the years that... 

Synthetic utility of stereoselective alkylations in natural product chemistry is exemplified by the preparation of optically active 2-arylglycine esters (38). Chirally specific a-amino acids with methoxyaryl groups attached to the a-carbon were prepared by reaction of the dimethyl ether of a chiral bis-lactam derivative with methoxy arenes. Using SnCl as the Lewis acid, enantioselectivities ranging from 65 to 95% were obtained. 

Succinic acid [110-15-6] (butanedioic acid 1,2-ethanedicarboxylic acid amber acid), occurs frequendy in nature as such or in the form of its esters. 

The sulfuric acid esters as compared to the sulfurous esters are the most widely used. In nature they appear as so1iibifi2ing groups in... 

Carboxylic Acid Esters. In the carboxyflc acid ester series of surfactants, the hydrophobe, a naturally occurring fatty acid, is solubilized with the hydroxyl groups of polyols or the ether and terminal hydroxyl groups of ethylene oxide chains. 

Triterpenes. The triterpenes (30 carbon atoms) are widely found in nature, especially plants, both in the free state and as esters or glycosides. A smaller but important group, including lanosterol [79-63-0] (114), occurs in animals. The triterpene hydrocarbon, squalene [111-02-4] (115), occurs in the hver oils of certain fish, especially those of sharks. 

Benzoic acid in the free state, or in the form of simple derivatives such as salts, esters, and amides, is widely distributed in nature. Gum benzoin (from styrax ben in) may contain as much as 20% benzoic acid in the free state or in combinations easily broken up by heating. Acaroid resin (from anthorrhoca haslilis) contains from 4.5 to 7%. Smaller amounts of the free acid are found in natural products including the scent glands of the beaver, the bark of the black cherry tree, cranberries, pmnes, ripe cloves, and oil of anise seed. Pern and Tolu balsams contain benzyl benzoate the latter contains free benzoic acid as well. The urine of herbivorous animals contains a small proportion of the glycine derivative of benzoic acid, hippuric acid [495-69-2] (CgH CONHCH2COOH). So-called natural benzoic acid is not known to be available as an item of commerce. 

Phenyl-2-propen-l-ol [104-54-1], commonly referred to as cinnamyl alcohol, is a colorless crystalline soHd with a sweet balsamic odor that is reminiscent of hyacinth. Its occurrence in nature is widespread as, for example, in Hyacinth absolute (Hyacinthus orientalis) (42), the leaf and bark oils of cinnamon Cinnamomum cassia, Cinnamomum lancium, etc), and Guava fmit [Psidiumguajava L.) (43). In many cases it is also encountered as the ester or in a bound form as the glucoside. 

Essential oils are obtained from fmits and flowers (61,62). Volatile esters of short- and medium-chain carboxyHc acids or aromatic carboxyHc acids with short- and medium-chain alcohols are primary constituents of essential oils, eg, ethyl acetate in wines, brandy, and in fmits such as pineapple ben2yl acetate in jasmine and gardenia methyl saHcylate in oils of wintergreen and sweet birch. Most of these naturally occurring esters in essential oils have pleasant odors, and either they or their synthetic counterparts are used in the confectionery, beverage, perfume, cosmetic, and soap industries (see Oils, essential). 

Perfumes, Flavors, Cosmetics, and Soap. Many naturally occurring esters in essential oils and some synthetic esters are important fragrance and flavor compounds (61,62). They are used in perfumes, flavors, cosmetics, soaps, detergents, and air fresheners. Benzyl, butyl, ethyl, methyl, and phenyl esters of benzoic acid are used as flavors, perfumes, and food preservatives. Glyceryl 4-aminobenzoate [136-44-7] and 2-ethyUiexyl 4-dimethylaminobenzoate [21245-02-3] are used in cosmetic sunscreen preparations. Alkyl esters of 4-hydroxybenzoic acid, called parabens, have been used under various names for fungus infections of the skin, and as preservatives in lotions and creams (101). Soap and cosmetic fragrances use large amounts of amyl and benzyl saHcylate. Benzyl saHcylate [118-58-1] is also used in deodorant sprays. 2-Ethylhexyl saHcylate [118-60-5] and 2-ethylhexyl 4-methoxycinnamate [5466-77-3] are used in sunscreen formulations (102). 

With these polymers hard blocks with T s well above normal ambient temperature are separated by soft bloeks which in the mass are rubbery in nature. This is very reminiscent of the SBS triblock elastomers discussed in Chapter 11 and even more closely related to the polyether-ester thermoplastic elastomers of the Hytrel type deseribed in Chapter 25. 

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