Esters isolation

A sodium carbonate solution of the crude acetic acid was washed with ether and then acidified with hydrochloric acid the required acid was isolated via an ether extraction and was esterified by refluxing for 6 hr with ethanol (370 ml) and concentrated sulfuric acid (15 ml). Excess alcohol was distilled, the residue diluted with water and the required ester isolated in ether. Distillation finally gave ethyl 2-fluoro-4-biphenylacetate,BP 134°C to 136°C/0.25 mm. 

Sodium ethoxide from sodium (3.67 g) in absolute alcohol (64 ml) was added over 20 minutes with stirring to a mixture of ethyl 4-i-butylphenylacetate (28.14 g) and ethyl carbonate (102 ml) at lOO C. The reaction flask was fitted with a Fenske column through which alcohol and then ethyl carbonate distilled. After 1 hour when the still head reached 124°C heating was discontinued. Glacial acetic acid (12 ml) and water (50 ml) was added to the stirred ice-cooled mixture and the ester isolated in ether, washed with sodium carbonate solution, water and distilled to give ethyl 4-i-butylphenylmalonate. 

This was dissolved in 550 ml of absolute benzene and the so-formed solution added to a mixture of 248 ml of absolute methanol and 550 ml of absolute benzene. After the exothermic reaction had terminated, the reaction mixture was boiled for a further 20 hours, then concentrated in vacuo and the product, 4-methylbenzoic acid methyl ester, isolated by conventional means. It could be purified by distillation, and the purified product boiled at 91°C/9 mm Hg, MP 32°C. 

Figure 4. Infrared spectrum of methyl-transrpyrethrate Prepared from pyrethric acid isolated from hydrolysis mixture of pyrethrum concentrate. Pure ester isolated by gas chromatography...

Harikumar, K. B., C. V. Nimita et al. (2008). Toxicity profile of lutein and lutein ester isolated from marigold flowers (Tagetes erecta). Int. J. Toxicol. 27(1) 1-9. 

There is the often-overlooked group of polyphenols containing the derivatives of hydro-xycinnamic and hydroxybenzoic acids such as caffeic, chlorogenic, and gallic acids (Figure 29.8), which occur in food and exhibit certain antioxidant activity. For example, some caffeic acid esters isolated from propolis from honeybee hives showed antiinflammatory... 

Examples of other antiviral fiavonoids isolated from medicinal plants also included luteolin-7-O-glucoside isolated from Youngia japonica (L.) DC. (Asteraceae), ° and three new fiavones named 5-carboxymethyl-4, 7-dihydroxyfiavone, its ethyl ester and butyl ester isolated from Selaginella moellendorjfii Hieron (Selaginellaceae), which displayed inhibitory activity in vitro on hepatitis B virus (HBV). ... 

Later, we described the isolation of a second type of cannabinoid receptor ligand, 2-arachidonoyl glycerol (2-AG) (K = 5-85 0.12 xM), an ester isolated from canine gut. " This was the first putative endogenous cannabinoid receptor ligand isolated from a peripheral tissue. Later, Sugiura et al isolated independently this compound from brain. 

Methyl Esters Isolated in Oxidizing White Fir Wood ... 

Chemical synthesis of 1-phosphate esters of 2-amino-2-deoxy-n-glucose has been described.37 127 Reaction of 3,4,6-tri-0-acetyl-2-amino-2-deoxy-a-D-glucosyl bromide hydrobromide (XLII) with triethylammonium diphenyl phosphate gave the l-(diphenyl phosphate) ester, isolated as its hydrochloride (XLIII). Cleavage of the phenyl groups and subsequent deacetylation gave 2-amino-2-deoxy-D-glucosyl phosphate as the crystalline, dipolar-ionic, monopotassium salt (XLV). 

Figure 6. Capillary GC-separation of R-(+)-derivatives of secondary alcohols and their esters, isolated by preparative GC from yellow and purple passion fruits (DB 210, 30 m/0.33 mm i.d., 140 °C, pentanol-2 OV 101, 50 m/0.33 mm i.d., 170 °C, heptanol-2).

Figure 4. Normal phase high-pressure liquid chromatography of cholesterol esters isolated from atherosclerotic lesions of human aorta (I), free cholesterol (II), oxygenated cholesterol esters (III), cholesteryl arachidonate (IV), cholesteryl linoleate (V), cholesteryl oleate and cholesteryl palmitate.

Figure IV. Capillary GC-separation of (R)-(+)-MTPA-derivatives of secondary alcohols and their esters, isolated by preparative GC from yellow and purple passion fruits.

Two groups, those of Corey and Sih, have reported studies on chemical analogs of the proposed biochemical mechanism, in which they activated the hydroperoxide function by forming the corresponding mesylate or trifluoromethanesulfonate (triflate). In no case were the peroxy esters isolated as they underwent elimination under the conditions of formation, even at -110 C. 

The Taxane Diterpenes.— The taxane skeleton represents an alternative mode of cyclisation of the macrocyclic diterpene hydrocarbon. Seven new taxane derivatives have been isolatedfrom Taxus baccata and characterised on the basis of spectroscopic and other data. Their structures are summarised in the following formulae (136a—g). In addition, the structure of baccatin-III (137), one of a group of complex esters isolated from the same source, has been com-pleted. The application of the olefin Octant rule to the taxane A double bond leads to the absolute configuration of these diterpenes. 

Caffeic acid phenethyl ester, isolated from the propolis found in bee hives, has also been shown to induce apoptosis in different cell lines, probably by modulating the redox state of cells. This ester was studied under different experimental conditions and in the presence of various agents, including Bcl-2, which protects cells from oxidative stress. Indeed, this agent had a protective effect against the apoptosis induced by caffeic acid phenethyl ester [159,160]. 

This reaction is carried out as follows First the formic ester is prepared of the tertiary alcohol that is to be esterified with a desired carboxylic acid. This is done by heating the tertiary alcohol for several days with the mixed anhydride of formic and acetic acid. This formic ester, isolated as usual, is mixed with an equivalent amount of the methyl ester of the other carboxylic acid, treated with 0.05 equivalent each of the free tertiary alcohol and sodium, and heated at 100-120°. The lowest-boiling component of the equilibrium mixture slowly distils off, namely, methyl formate. The reaction is sometimes quite vigorous and is usually complete in 3-4 h. After the free alkali has been neutralized with acetic acid, the distillation residue is worked up in the usual way. 

Hypotensive effects of methanolic extract of L. multiflora leaves collected in Ivory Coast seem to be due to a caffeic ester isolated from a phenolic fraction. The compound induced a marked and long-lasting tensional fall at 2mg/kg i.v, the decrease in systolic arterial blood pressure was high as- 40% and lasted for more than 15 minutes [55],... 

Table 5. Aristolochic Acid Alkyl Esters Isolated from Aristolochia Species...

SOLUTION Start with a single stereoisomer of an alcohol whose OH group is bonded to an asymmetric carbon, and determine the specific rotation of the alcohol. Then convert the alcohol into an ester, using a method that does not break any bonds to the asymmetric carbon. Next, hydrolyze the ester, isolate the alcohol obtained from hydrolysis, and determine its specific rotation. 

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