Protection function

Protect functional groups which may be incompatible with a set of reaction conditions... 

M (marginal) indicates that the stability of the protected functionality is marginal, and depends on the exact parameters of the reaction. The protective group may be stable, may be cleaved slowly, or may be unstable to the conditions. Relative rates are always important, as illustrated in the following example (in which a monothioacetal is cleaved in the presence of a dithiane), and may have to be determined experimentally. 

L (low) indicates that the protected functionality is stable under the reaction conditions. ... 

The reactivities in the charts refer only to the protected functionality, not to atoms adjacent to the functional group for example, RCOOEt L (low)... 

Dibromo adducts have been used for many years for purifying olefins. Reduction with zinc or iodide has been the traditional way of regenerating the olefin, although occasionally other reagents, ferrous chloride, for example, have been employed. Zinc is usually effective and may be used in acetic acid in favorable cases. Milder conditions are necessary if sensitive groups are present (ref. 185, p. 51). A well known application of the protective function... 

An advantage of Tiffeneau ring enlargement and rearrangement of 17a-hydroxy-20-keto steroids for preparing of D-homosteroids is the ready availability of the starting 17-ketones. Both procedures involve mild conditions which allow a wide variety of suitably protected functional groups to be present. 

The designation TN is subdivided, depending on the arrangement of neutral and protective conductors. S indicates that separate conductors and C that neutral and protective functions are provided by a single conductor provide neutral and protective functions. 

TN-C system Neutral and protective functions combined in a single conductor throughout the system. 

Aspirin and other NSAIDs function by blocking the cyclooxygenase (COX) enzymes that carry out the body s synthesis of prostaglandins (Sections 7.11 and 27.4). There are two forms of the enzyme, COX-1, which carries out the normal physiological production of prostaglandins, and COX-2, which mediates the body s response to arthritis and other inflammatory conditions. Unfortunately, both COX-1 and COX-2 enzymes are blocked by aspirin, ibuprofen, and other NSAIDs, thereby shutting down not only tire response to inflammation but also various protective functions, including the control mechanism for production of acid in the stomach. 

Protecting group (Sections 17.8, 19.10, 26.7) A group that is introduced to protect a sensitive functional group towrard reaction elsewhere in the molecule. After serving its protective function, the group is removed. 

The next major obstacle is the successful deprotection of the fully protected palytoxin carboxylic acid. With 42 protected functional groups and eight different protecting devices, this task is by no means trivial. After much experimentation, the following sequence and conditions proved successful in liberating palytoxin carboxylic acid 32 from its progenitor 31 (see Scheme 10) (a) treatment with excess 2,3-dichloro-5,6-dicyano-l,4-benzoquinone (DDQ) in ie/t-butanol/methylene chloride/phosphate buffer pH 7.0 (1 8 1) under sonication conditions, followed by peracetylation (for convenience of isolation) (b) exposure to perchloric acid in aqueous tetrahydrofuran for eight days (c) reaction with dilute lithium hydroxide in H20-MeOH-THF (1 2 8) (d) treatment with tetra-n-butylammonium fluoride (TBAF) in tetrahydrofuran first, and then in THF-DMF and (e) exposure to dilute acetic acid in water (1 350) at 22 °C. The overall yield for the deprotection sequence (31 —>32) is ca. 35 %. 

Neuronal excitotoxicity AEA levels are elevated in the hippocampus of mice treated with kainic acid. 2-AG levels are elevated in rats treated with pilocarpine These are two animal models of epileptic seizures, where the endocannabinoids play an anti-convulsant and protective function Inhibitors of cellular re-uptake... 

In addition to the careful selection of structural metals, the cathodic protection of water-wetted parts may also be specified. For most boiler plant systems, however, because of the tortuous and extended waterside surfaces involved, the use of cathodic protection is only a partial solution to controlling corrosion and should never be the sole secondary protocol. Rather, cathodic protection functions well when employed as part of a more comprehensive program that includes appropriate internal chemical treatments. 

Besides its protective function of the labile phosphine group, the BHj group activates the adjacent substituents such as methyl group or P-H bond to deprotonation with a strong base [78]. This methodology provides an efficient alternative to the difficult synthesis of a variety of optically active tertiary phosphine derivatives, as will be described in Sect. 3. 

Collman JP, Boulatov R, Shrryaeva IM, Sunderland CJ. 2002b. The distal Cu ion protects functional heme/Cu analogs of cyctochrome oxidase from inhibition by cyanide and CO. Angew Chem IntEd 41 4139. 

Further examples for the preparation of 4(5)-substituted imidazoles with AT-sulfa-moylimidazoles are given below. In these cases both the sulfamoyl and the silyl groups are used as protecting functions (bisprotection of the imidazole moiety). 163... 

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