Selective derivatization

Ph3COSiMc3, Me3SiOTf, CH2CI2, 0°, 0.5 h, 73-97% yield. These conditions will also introduce the trityl group on a carboxyl group. The primary hydroxyl of persilylated ribose was selectively derivatized. 

Tetrasubstituted thiophenes obtained by the Gewald reaction serve as templates for structural diversification and semi-automated library synthesis. Thiophene 31, prepared from 3-ketoester 29 and t-butylcyanoacetate 30, could be selectively derivatized at three of the four substituents to maximize library diversity. This procedure represents an improvement over previously published methods for utilizing 1,3-dicarbonyl compounds in the Gewald reaction. 

It is important not only that a multiplicity of compounds in the sample mixture may be selectively derivatized - as was shown for Type III reactions - but also that one racemate may be derivatized with a multiplicity of derivatizing agents (Fig. 7-17). Although this approach can be used to optimize the analogues of a compound [28, 29], it is of special interest when a compound is required to be separated on a preparative scale. 

Finally, Chapter 7 discusses the use of selected fluorescence and pH indicator detection reagents, nniversal charring methods, and selective derivatization reagents that produce colored zones. 

Selective derivatization of parent TACN427 and particularly syntheses of a large number of linked-TACN428,429 resulted in the isolation of interesting complexes (527) (the solid-state structure of this complex also contains an aggregate of [Na(BF4)2] units which form a polymeric... 

The aldehyde 38 was obtained from 35, by way of 36 and 37, by the carbodiimide—dimethyl sulfoxide oxidation procedure52 in the presence of 3-(3-dimethylaminopropyl)-l-ethylcarbodiimide hydrochloride (EDAC)53 and dichloroacetic acid. It was isolated in the form of its crystalline 1,3-diphenylimidazolidine derivative (39) by trapping the freshly prepared aldehyde 38 with N,N -diphen-ylethylenediamine. (This reagent was developed by Wanzlick and Lochel54 for the selective derivatization of aldehydes, and has been exploited for the isolation of nucleoside 5 -aldehydes55 and other aldehydo derivatives of carbohydrates by Moffatt and coworkers.52(b))... 

Fig. 13 A semi-synthetic abzyme. Selective derivatization of lysine-52 in the heavy chain of MOPC315 creates a thiol, then bonded to an imidazole, which gives an abzyme capable of improved hydrolysis of coumarin ester [42] with ca, = 0.052 min-1.

In one example, 3-phenylcyclobutanone was isolated by a nonchromatographic method by using selective derivatization as the hydrogen sulfite adduct in 22% yield.4... 

Tertiary amines can also be selectively derivatized with citric acid on acetic acid anhydride, a mixture that is mixed with the eluent after chromatography and then heated to 393 K to develop a violet-red color (237). Absorbance is measure at 550 nm but some compounds can show strongly tailing peaks. 

The following four chapters offer insight and experimental details in the selective derivatization of sugar molecules. 

In addition to the binding constant and safety considerations, economics, and quality control issues also play a role in considering which ligands to use. Because of the difLculty in selectively derivatizing a speciLc hydroxyl or family of hydroxyls, most modiLed CDs of pharmaceutical interest are likely to be complex mixtures (Stella and Rajewski, 1997). Methods to characterize these mixtures, therefore, need to be in place to assure lot-to-lot reproducibility. The costs of acute and chronic safety studies required to evaluate any new CD derivatives are very high, and this prohibits them from being widely evaluated for pharmaceutical applications. 

An important issue is the differentiation between aldehyde and keto groups in cellulosic materials. Different approaches are theoretically conceivable a selective derivatization of either aldehyde and keto groups, a mathematical... 

Most of the inherently chiral calix[5]arenes described up to now, owe their chirality, however, to the asymmetric substitution pattern at the narrow rim, and due to the lack of other general, selective derivatization reactions are derived from 1,2-or 1,3-crown ethers. Both compounds possess a symmetry plane and can be desymmetrized by a single O-alkyl or O-acyl residue in position 3 (=5) or 4 (=5).151,152,153 In practice, 1,2-crown ethers 79 were prepared from mono-O-alkyl derivatives by reaction with the appropriate ditosylates, while 80 was obtained from the 1,3-crown-ether by subsequent O-alkylation or O-acylation using a weak base to benefit from the fact, that the first deprotonation leads to a hydrogen-bonded (4/5)monoanion. The picolyl derivatives 79 (n = 2) were resolved by HPLC... 

NM R experiments (ID and 2D, homonuclear and heteronuclear) are the preeminent techniques for the determination of molecular structures. However, careful application and analysis of mass spectral data can provide sufficient information to postulate tentative structures. In this respect, the application of tandem MS experiments, sometimes in conjunction with selective derivatization of the unknown compound, can be very informative about the stmcture. The high-resolution mass spectral data are critical to the support of NMR-deduced stmctures by providing molecular formulae for unknowns. 

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