Hydroxamates, acyl

Treatment of O-acylated hydroxamic acids with base provides isocyanates. 

A-Alkylhydroxylamines react with substituted allyl acetates (e.g. 15, equation 11) in palladium catalyzed addition-elimination reactions giving the corresponding A-alkyl, A-allylhydroxylamines 16. The reaction proceeds with high regioselectivity but complete racemization. A similar reaction with 0-acyl hydroxamic acids has been carried out using allylic a-alkoxycarbonyloxyphosphonates. ... 

A clear-cut molecular relay system is materialized with the combination of two nucleophile moieties such as hydroxamic acid and imidazole introduced in a polymer (38, 40, 82). Hydroxamate anion has a high nucleophilicity but deacylation of the acylhydroxamate is very slow. The significance of the deacylation step in the hydrolysis in polymer catalyst is pointed out in several works, for example, the deacylation of acetylated poly(4(5)-vinylimidazole) (83,84) and the aminolysis of nitrophenyl ester of poly(styrene-co-acrylic acid) (85—87). To promote the deacylation velosity of the acylated hydroxamic acid imidazole moiety is introduced in the hydroxamic acid-containing polymer. The polymers are shown in tire following page. 

In addition, as is shown in Table 13, the deacylation which is represented in kd is increased by a factor of more than 103 in poly(PHA-IM-am), compared with poly(PHA-am). As is observed in the deacylation which is catalysed by imidazole moiety in the case of a-chymotrypsin, the catalysis by imidazole moiety in the deacylation of the acylated hydroxamic acid is considered. The turnover number, turnover hi poly(PHA-IM-am) is also high. The deacylation rate of poly(PHA-IM-am)... 

Fig. 10. EPR spectra of the effect of (upper panel) desferrioxamine and (lower panel) A -methyl-V-acyl hydroxamate on ferryl myoglobin species.

Cyclocondensation of malonyl derived O-acyl hydroxamic acid derivatives 6, in the presence of phosphazene super base P2-r-Bu 7, gave rise to isoxazolone carboxylic esters 8 <03TL7763>. 

P-Lactams.1 A biomimetic synthesis of /3-lactams from chiral amino acids such as L-serine has been developed by Mattingly and co-workers. The protected amino acid (1) is first converted into the O-alkyl or O-acyl hydroxamate (2), which undergoes cyclization to derivatives of l-hydroxy-2-azetidinones on treatment with triphenylphosphine-carbon tetrachloride. This cyclization is also possible with triphenylphosphine-diethyl azodicarboxylate.2 The final step involves reduction of the N—OH group with TiClj.3 The advantage of this method over that of Wasserman (9,428), which involves cyclization of /3-haloamides, is that a strong base such as NaH is not required. 

Rearrangement of O-acyl hydroxamic acid derivatives with base or heat to amines or urea derivatives (via isocyanates), or rearrangement of carboxylic acids via their hydroxamic acids to amines (see 1st edition). 

The most significant synthetic route to these compounds is the condensation of A-(a-hydroxy-acyl)hydroxamic acids with carbonyldiimidazole (Equation (23)) or aromatic aldehydes (Equation... 

Clark, A.J., Al-Faiyz, Y.S.S., Patel, D. and Broadhurst, M.J. (2001) Rearrangement of unactivated A-alkyl-O-benzoyl hydroxamic acid derivatives with phosphazene bases. Tetrahedron Letters, 42, 2007-2009 Clark, A.J., Patel, D. and Broadhurst, M.J. (2003) Base-mediated reaction of A-alkyl-O-acyl hydroxamic acids synthesis of 3-oxo-2,3-dihydro-4-isoxazole carboxylic ester derivatives. Tetrahedron Letters, 44, 7763-7765. 

Acyl hydroxamates Acylurethans Carbamic carboxylic anhydrides (25)... 

Via intermediates Acyl hydroxamates from hydroxamic acids... 

N-(Acoxy)acylamines N-Acylamide acetals 1 -Acylamino-l-peroxides Acyl hydroxamates Acylurethans Carbamic carboxylic anhydrides... 

Lessen (reaction of an 0-acyl hydroxamic acid with formation of an 0-leaving group)... 

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