Sensitivities of functional groups

Table 1.3. Sensitivity of Functional Groups to Jones Oxidation...

Using this kind of analysis one can address the sensitivity of functional group response to a particular CSP. Focused information concerning functionality along with the physicochemical causes of enantioselection can be derived. This type of computational approach is complementary to that described by Isaksson [51] and by... 

Table I Sensitivities of Functional Groups to Reaction Conditions...

As indicated above, the penetration depth is on the order of a micrometer. That means that in ATR, absorption of infrared radiation mostly occurs within a distance 8 of the surface and ATR is not as surface sensitive as some other surface analysis techniques. However, ATR, like all forms of infrared spectroscopy, is very sensitive to functional groups and is a powerful technique for characterizing the surface regions of polymers. 

Schemes are available, however, that start from the free carboxylic acid, plus an activator . Dicyclohexylcarbodiimide, DCC, has been extensively employed as a promoter in esterification reactions, and in protein chemistry for peptide bond formation [187]. Although the reagent is toxic, and a stoichiometric concentration or more is necessary, this procedure is very useful, especially when a new derivative is targeted. The reaction usually proceeds at room temperature, is not subject to steric hindrance, and the conditions are mild, so that several types of functional groups can be employed, including acid-sensitive unsaturated acyl groups. In combination with 4-pyrrolidinonepyridine, this reagent has been employed for the preparation of long-chain fatty esters of cellulose from carboxylic acids, as depicted in Fig. 5 [166,185,188] ...

Chemoselectivity of enzymatic reaction is the enzyme-catalyzed transformation of one type of functional group in the presence of other sensitive groups present in the substrate molecule. As a result, reactions catalyzed by enzymes generally tend to be cleaner and purification of product(s) from impurities can largely be omitted. Therefore, all enzymatic reactions generate less by-products and waste compared to chemical transformations. This simplifies all operations and reduces costs of transformation, which is of great importance for the industry. 

The reaction tolerates a variety of functional groups, especially the acid-sensitive acetal (81b), carbamate (81c) and the benzyl triazole (81d-f, and 81h, j). These intermediates, which are unstable under the conditions of the traditional Fischer indole reaction, were conveniently synthesized using this method. The structurally... 

In 1991, Li and Chan reported the use of indium to mediate Barbier-Grignard-type reactions in water (Eq. 8.49).108 When the allylation was mediated by indium in water, the reaction went smoothly at room temperature without any promoter, whereas the use of zinc and tin usually requires acid catalysis, heat, or sonication. The mildness of the reaction conditions makes it possible to use the indium method to allylate a methyl ketone in the presence of an acid-sensitive acetal functional group (Eq. 8.50). Furthermore, the coupling of ethyl 2-(bromomethyl)acrylate with carbonyl compounds proceeds equally well under the same reaction conditions, giving ready access to various hydroxyl acids including, for example, sialic acids. 

The transformations discussed in Sects. 2.2-2.3 highlight several important features of the RCM process. Firstly, the compatibility of the ruthenium initiator 3 with a wide range of functional groups including epoxides, vinyl iodides, thia-zoles and alcohols is demonstrated. The versatility of 3 is further illustrated in Sect. 2.3, where it is used to effect RCM of polymer-bound substrates. Previously, the molybdenum complex 1 has been reported to be more sensitive than 3 [19]. Experiments reported here are consistent with this view (Sect. 2.2.3) [14b]. 

FIGURE 3.4 Deprotection of functional groups by reduction with sodium in liquid ammonia [du Vigneaud et al., 1930]. As in Figure 3.3, except reduction is effected by solvated electrons and protons are provided by water at the end of the reaction. Excess sodium is destroyed by NH4C1. This is a simplified presentation of the reaction. AH benzyl-based protectors as well as -Arg(N02)-, -Arg(Tos)-, and -His(Tos)- are sensitive to sodium in liquid ammonia. 

The ion-exchangers used in LC consist either of an organic polymer with ionic functional groups, or silica coated with an organic polymer with ionic functional groups. The types of functional groups used are the same as described in Chapter 18. Since IEC can be carried out with an aqueous mobile phase near physiological conditions, it is an important technique in the purification of sensitive biomolecules such as proteins. 

Proteins contain a variety of functional groups and interact with the stationary phase at a number of simultaneous sites on the protein molecule, each more or less affected by change in eluent, or mobile-phase, pH or ionic strength. The equilibrium constant for the dissociation of the adsorption complex thus contains a product of many eluent-sensitive concentration terms, and the equilibrium position is very sensitive to elution conditions. Under the elution conditions, some proteins in a mixture may be tightly bound by the stationary phase (t), oo) while others are unretained (t R 0). Differential migration (Section 19.2.1) is replaced by extreme retention values. 

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