Cleavage derivatives

Tryptophan modification, peptide-bond cleavage derived from skatole, which is also known as boar taint. 

The low reactivity of aliphatic ethers renders the problem of the preparation of suitable crystalline derivatives a somewhat difficult one. Increased importance is therefore attached to the physical properties (boding point, density and refractive index) as a means for providing preliminary information. There are, however, two reactions based upon the cleavage of the ethers which are useful for characterisation. 

The /-butoxycarbonyl group (Boc, "t-box ) has been eMens vely used in peptide synthesis, and Boc derivatives of many amino acids are commercially available. The customary reagent for the preparation from the amine is t-butyl azidoformate in water, dioxane/water, DMSO, or DMF. The cleavage by acids of medium strength proceeds with concomitant loss of isobutene and carbon dioxide (L.A. Carpino, 1957, 1973 see section 4.1.2.2). 

The most common stereoselective syntheses involve the formation and cleavage of cyclopentane and cyclohexane derivatives or their unsaturated analogues. The target molecule (aff-cts)-2-methyl-l,4-cyclohexanediol has all of its substituents on the same side of the ring. Such a compound can be obtained by catalytic hydrogenation of a planar cyclic precursor. Methyl-l,4-benzoquinone is an ideal choice (p-toluquinone M. Nakazaki, 1966). 

Several cortisone derivatives with glucocorticoid effects are most active, if they contain fluorine in the 9or-position together with an Il(9-OH group. Both substituents are introduced by the cleavage of a 9,11 -epoxide with hydrogen fluoride. The regio- and stereoselective formation of the -epoxide is achieved by bromohydrination of a 9,11-double bond and subsequent alkali treatment (J. Fried, 1954). 

The C-S bond in purine derivatives undergoes cleavage under mild conditions by nucleophilic agents such as benzylmercaptan or glutathione in dimethylformamide with a phosphate buffer of pH 6.5 (277). The salt (110) of dithiazolylsulfide heated at 190 C yields the A-4-thiazo-line-2-thione (112) and 2-chlorothiazole (111) (Scheme 56) (278-280). 

The thiazolium is not acidic enough for observing directly solvation of the molecule (or an hydrolysis and subsequent cleavage of the ring) (24) without adding a base, as it is the case for benzoxazolium or benzothiazolium. With the same dilution (10 mole liter ), it is necessary to add sodium ethylate to the solution of 2-methyl-4.5-diphenylthiazolium to observe the equilibrium described above. A new band appears in the UV spectrum at 320 nm that is attributed to the ethoxy derivative by analogy to what has been observed with other benzothiazoliums (26),... 

Active Raney nickel induces desulfurization of many sulfur-containing heterocycles thiazoles are fairly labile toward this ring cleavage agent. The reaction occurs apparently by two competing mechanisms (481) in the first, favored by alkaline conditions, ring fission occurs before desul-, furization, whereas in the second, favored by the use of neutral catalyst, the initial desulfurization is followed by fission of a C-N bond and formation of carbonyl derivatives by hydrolysis (Scheme 95). 

In a study aimed at identifying thiazole derivatives, Travagli (485) obtained the ring cleavage of 2-aminothiazoIes (205) by their phenyl-hydrazinolysis in acetic acid. 

Mass Spectrometry A prominent peak m the mass spectra of most carboxylic acid derivatives corresponds to an acyhum ion derived by cleavage of the bond to the car bonyl group... 

The outer layer or cortex of the adrenal gland is the source of a large group of sub stances known as corticosteroids Like the bile acids they are derived from cholesterol by oxidation with cleavage of a portion of the alkyl substituent on the D ring Cortisol IS the most abundant of the corticosteroids but cortisone is probably the best known Cortisone is commonly prescribed as an antiinflammatory drug especially m the treat ment of rheumatoid arthritis... 

The oxidation may be carried out with an inert solvent thermally (35), with a sensitizer such as bromine (36), with uv radiation (37), or over a suitable catalyst (38). Principal by-products of all these oxidation processes are the acyl fluoride products derived from oxidative cleavage of the perfluoroaLkene (eq. 

Oxidative cleavage of P-aminoacyl complexes can yield P-amino acid derivatives (320,321). The rhodium(I)-catalyzed carbonylation of substituted aziridines leads to P-lactams, presumably also via a P-aminoacyl—metal acycHc compound as intermediate. The substituent in the aziridine must have 7T or electrons for coordination with the rhodium (322,323). 

Some unsaturated ketones derived from acetone can undergo base- or acid-catalyzed exothermic thermal decomposition at temperatures under 200°C. Experiments conducted under adiabatic conditions (2) indicate that mesityl oxide decomposes at 96°C in the presence of 5 wt % of aqueous sodium hydroxide (20%), and that phorone undergoes decomposition at 180°C in the presence of 1000 ppm iron. The decomposition products from these reactions are endothermic hydrolysis and cleavage back to acetone, and exothermic aldol reactions to heavy residues. 

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