Acylated bases

OF SUBSTITUTED AROMATIC AMIDES (AROMATIC ACYLATED BASES)... 

The formation of acylium ions by the fission of the hydroxyl group in strong acid provides a useful source of electrophilic carbon and this leads to an important series of methods for making C-C bonds (Scheme 3.59), similar to the Friedel-Crafts acylations based on acyl chlorides. The acylium ion obtains some stabilization from the lone pairs on the oxygen atom of the carbonyl group (see 3.23). 

A related strategy was used for synthesis of a more complex carbohydrate, the trisaccharide moiety of globotriaosyl ceramide (Gb3) [10b] (Scheme 3.19). In this reaction an acyl-based fluorous protecting group was used to facilitate the intermediate purification steps in a similar way as can be achieved by solid phase carbohydrate chemistry [12]. 

The first syntheses of the homoerythrinane framework are following the assumed hiosynthetic route. Thus, the N-protected 1-phenethyliso-quinoline 196 (Scheme 35) can be cyclized by a phenol oxidative procedure providing the tetracyclic naphthalenoisoquinoline 197, a homologue of neoproaporphine (35) in 35-45% yield (105). This has been transformed to the dibenzazecine intermediate 198 by ring reopening. Finally, the N-deprotected free amine base can be oxidized giving homoerysodienone (199) (106, 107). A diphenoquinone type intermediate 38 (Scheme 1 n = 2) is not available from the N-acylated base 198. 

Ornithine formation. Occurs when protonation or acyl-based groups are used for protection of the guanidine side-chain... 

Many authors include these reactions among acylations, based on the similarity of the processes and the nomenclature of some reagents, for example from picric acid (13) one prepares picryl chloride which yields a picramide according to equation (18). 

The soda-lime test (preliminary tests) decomposes acylated bases into the base and the parent acid, though the latter may then be decarboxylated to a hydrocarbon. Hydrolysis of these compounds by alkali is often slow, and the following method is preferable. 

De Lago, E. Gustafsson, S. B. Femandez-Ruiz, J. Nilsson, J. Jacobsson, S. O. R Fowler, C. J. Acyl-based anandamide uptake inhibitors cause rapid toxicity to C6 glioma cells at pharmacologically relevant concentrations. J. Neurochem. 2006, 99, 677-688. 

The sensitivity of 7V-acylated bases to acid 5 -OH deprotection conditions has been a stimulus to investigating A -nonacylated nucleoside phosphate or phosphite synthons (59,60). Using the same principle recently in polymer supported synthesis, S. M. Gryaznov and R. L. Letsinger (di), however, recommend an additional debranching step during each cycle, which makes the use of iV-unprotected synthons less advantageous, at least for routine preparations. 

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