Isopropyl esters deriv

Figure 14.8 Partial m/z 44 and m/z 45/44 traces obtained by GC C IRMS analysis of commonly occurring amino acids (as their triflouroacetyl isopropyl ester derivatives) together with a range ofco injected internal standards...

The enantiomeric excess values of the (S)-cyanohydrins are obtained from the ( + )-(R)-Mosher ester derivatives [a-methoxy-a-(trifluoromethyl)phenylacetates], whereas the corresponding benzeneacetic acids are first converted into their isopropyl carboxylates which then yield the ( + )-(ft)-Mosher ester derivatives. 

Tipson devoted most of his years in Levene s laboratory accomplishing seminal work on the components of nucleic acids. To determine the ring forms of the ribose component of the ribonucleosides he applied Haworth s methylation technique and established the furanoid structure for the sugar in adenosine, guanosine, uridine, and thymidine. He showed that formation of a monotrityl ether is not a reliable proof for the presence of a primary alcohol group in a nucleoside, whereas a tosyl ester that is readily displaced by iodide affords clear evidence that the ester is at the 5-position of the pentofuranose. Acetonation of ribonucleosides was shown to give the 2, 3 -C -isopropyl-idene derivatives, which were to become extensively used in nucleoside and nucleotide chemistry, and were utilized by Tipson in the first chemical preparation of a ribonucleotide, inosinic acid. 

For amino acid analysis the labeled protein needs to be hydrolyzed and derivatized. Most commonly the hydrolysis is performed in 6 M HC1, and the amino acids are converted into their isopropyl ester and pentafluoropropanamide derivatives (Fig. 1.1) before GC/ MS analysis. The molecular ion is not always visible after standard electron impact (El) ionization, and the fragment after loss of the carboisopropoxy group is the highest observable peak. This leaves m/e=175 plus the mass of the amino acid side chain, from which the degree of labeling can be directly deduced. 

Figure 11. Enantiomer separation of proteinogenic a-amino acids as lheir /V(O.S)-pentafluoroprOpanoyl isopropyl esters (histidine as Vii"-ethoxycarbonyl derivative) on Chirasil-Val [20 m x 0.27 mm (i.d.) glass capillary column. 85-185"C, 0.35 bar hydrogen]. All D-enantiomers are eluted before the L-enantiomers126 111.

Gemfibrozil is absorbed quantitatively from the intestine and is tightly bound to plasma proteins. It undergoes enterohepatic circulation and readily passes the placenta. The plasma half-life is 1.5 hours. Seventy percent is eliminated through the kidneys, mostly unmodified. The liver modifies some of the drug to hydroxymethyl, carboxyl, or quinol derivatives. Fenofibrate is an isopropyl ester that is hydrolyzed completely in the intestine. Its plasma half-life is 20 hours. Sixty percent is excreted in the urine as the glucuronide, and about 25% in feces. 

Trifluoroacetyl derivatives of amines were resolved on trifluoro-acetylated-L-valyl-L-valine isopropyl ester coated in capillary columns. Better efficiency was obtained when a ureide, which was formed by the condensation of phosgene with L-Valine isopropyl ester, was coated on glass capillaries of about 70 meters in length and 0.25 mm i.d. Purity of the reagent (column coating) will affect resolution but not the relative peak areas. 

Topical PGE2 and PGF2qi significantly reduce intraocular pressure for at least 24 hours and are used in the treatment of glaucoma. Derivatives of the isopropyl ester of PGF2qi appear to be the most effective. Transient ocular adverse effects include conjunctival hyperemia, local irritation, intermittent photophobia, and pain in the eye (66-68). Newer derivatives, such as latanoprost, travoprost, and bimatoprost, appear to be better tolerated, with less severe and less frequent adverse effects (69). They reduce intraocular pressure by increasing uveoscleral outflow. 

Several polyamides and polyurethanes have been synthesized by condensation polymerization and used as the precursors for the preparation of different CSPs. These CSPs showed different chiral recognition properties than those of addition polymers. AUenmark and Andersson [67] prepared a CSP containing silica gel supported by v-triazinc derivatives of L-valine isopropyl esters (Fig. 14) and the... 

FIGURE 14 Structure of polyamide-based CSP (.s-triazi ne derivative of L-valine isopropyl ester) (condensation polymer). (From Ref. 37.)... 

Whilst the use of Taddol as an asymmetric phase-transfer catalyst for asymmetric Michael reactions was only moderately successful, it was much more enantioselec-tive in catalyzing alkylation reactions. For this study, Belokon and Kagan employed alanine derivatives lib and 16a-c as substrates, and investigated their alkylation with benzyl bromide under solid-liquid phase-transfer conditions in the presence of 10 mol % of Taddol to form a-methyl phenylalanine, as shown in Scheme 8.8. The best results were obtained using the isopropyl ester of N-benzylidene alanine 16b as substrate and sodium hydroxide as the base. Under these conditions, (R)-a-methyl phenylalanine 17 could be obtained in 81% yield and with 82% ee [19]. Under the same reaction conditions, substrate 16b reacted with allyl bromide to give (R)-Dimethyl allylglycine in 89% yield and with 69% ee, and with (l-naphthyl)methyl chloride to give (R)-a-methyl (l-naphthyl)alanine in 86% yield and with 71% ee [20]. 

Since aluminum alkoxides function effectively as catalysts for alcohol exchange in esters,38 89 reduction of keto esters by aluminum isopropoxide frequently yields the isopropyl ester of the hydroxy acid. Thus the reduction of the cyclopropane derivative XLIV gave the isopropyl ester of the reduced acid (XLV).40 Similarly the substituted methyl /3-keto ester (XLYI)41 gave upon reduction the isopropyl esters of the stereoisomeric reduced acids (XLVII). 

The above stereospecific tiirane polymerisations have generally been run in heterogeneous systems. Such conditions essentially make it impossible to determine the detailed structure of active species involved in these polymerisations. Thus, enantiosymmetric and enantioasymmetric polymerisations of propylene sulphide have also been studied in a homogeneous phase by using chiral cadmium thiolates of cysteine esters and chiral cadmium carboxylates of cysteine and methionine [157,160-164]. The most studied is living polymerisation using the cadmium derivative of the isopropyl ester of (.S)-cysteine [160] ... 

The important thing concerning volatility at various temperatures is the relative amount of material in the atmosphere at the different temperatures. If one knows the latent heat of vaporization, the tendency of the material to vaporize can be calculated from Equation 3. If we now consider preparations of derivatives whereby vapor loss can be reduced, it is immediately apparent that the latent heat of vaporization must be increased. This can be done with the phenoxyacetic acid compounds in preparing the so-called low volatile esters as represented by the butoxy-ethanol ester as illustrated in Table II. Determinations of the ratio of the latent heat of vaporization of the butoxyethanol ester to that of the isopropyl ester indicated a value of about 2. 

Several lactic acid derivatives were used by Gessner et al. for the determination of the enantiomeric purity of flavor substances such as chiral alcohols from natural sources. Diastereomeric 0-acetyl-, propionyl-, and hexanoyllactic acid esters of the chiral alcohols were separated by GLC (155). A report from the same laboratories described characterization of several chiral aroma substances that are S-lactones. The lactones were hydrolyzed to the corresponding hydroxy acids, and the acid moiety was esterified to the isopropyl ester. The remaining hydroxyl group was esterified with (R)-2-phenylpropionic add chloride or [30], and the diastereomeric derivatives were separated using preparative silica gel LC. The derivatives were also separated on an analytical scale by GLC (156). 

FAs are subjected to Ag-TLC usually in the form of methyl esters. The methods for methylation and transmethylation are simple, easy to perform, and with practically 100% yield. Methyl esters are particularly suitable when Ag-TLC is used as a complementary method with GC. Butyl and isopropyl esters were employed for the fractionation of butterfat FAs by Ag-TLC because these derivatives provided better resolution in GC. Conversion of positionally isomeric 18 1 and 20 1 FAs into phenacyl esters ensured complete resolution of the components by Ag-TLC however, this is not possible when using methyl esters. 

The rate of acetate fragmentation depends upon the nature of the alkyl group, with the relative rates of elimination of ethyl, isopropyl and /-butyl acetates being 1 26 1660, respectively, at 400 However, Hammett correlations for fragmentation of a- and 3-afyl-substituted acetates show little sensitivity to aryl substituents.The rates of fragmentation of esters derived from other carboxylic acids are dependent upon the pK of the parent acid, but this does not appear to influence significantly the regioselectivity... 

Carbonylbisphosphonate esters react smoothly with NH2OCH3. For example, reaction of the isopropyl ester gave the corresponding stable O-methyl oxime in 60% yield. The free oximes, and the corresponding oxime derivatives of acid bis-phosphonates, have not yet been subjected to systematic study. However, very preliminary work indicates that the free oxime of the parent acid in aqueous solution is unstable to fragmentation with C-P bond cleavage, similar to that encountered with the troika acids. 

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