White et al 38 reported the synthesis of hydroxamates using Deoxo-fluor; Katritzky et al 39 reported the synthesis of N-alkyl, O-alkyl and O, N-dialkyl hydroxamic acids via acyl benzotriazole intermediates; Gissot et al 40 reported high yielding one step synthesis of hydoxamates from various un-activated esters including enolizable esters and chrial α-amino acid esters and peptides ; Woo et al 41 reported the conversion of sterically hindered carboxylic acids to N-methoxy-N-methyl amides using 1.1eq of methanesulphonyl chloride; Martinelli et al 42 reported the palladium catalysed amino carbonylation of anyl bromides into the corresponding Weinreb amides; Nemoto et al 43 also reported a one pot synthesis of α-siloxy weinreb amides from aldelydes using N, O-dimethly amine and a masked acyl cyamide reagent bearing a tert-butyl dimethyl silyl group. Synthesis of Anticancer Hydroxamates Most hydroxamates used in cancer chemotherapy acts as histone deacetylase HDAC inhibitors. Histone deacetylase are a group of enzymes that removes acetyl groups from the lysine residues on a histone. The method has been success fully applied to enantiomerically pure esters without loss of stereochemical integrity. 1-Propanephosphonic Acid Cyclic Anhydride T3P Promoted Synthesis of Hydroxamic Acid1-Propanephosphonic acid cyclic anhydride T3P promotes the synthesis of hydroxamic acids from carboxylic acids. 34 Application of ultra-sonication was showed to accelerate this conversion. desferrioxamine B, fosmidomycin, siderophores 28 and allergic diseases. 29 The wide biological application of hydroxamates necessitates the review of its synthesis and biological applications. General Synthesis of Weinreb Amides Hydroxamic acids are prepared usually from esters or acid chlorides or carboxylic acids.2.1. Removal of the acetyl groups known as hypo acetylation restores the normal positive change to the histone and therefore allows the DNA to condense and prevent transcription. This silencing can become permanent if the unprotected lysines are then methylated.
A simple synthetic procedure allows the conversion of a wide variety of carboxylic acid to hydroxamates. Synthesis of Weinreb Amides Using Triazime Intermediates De Luca et al 37 reported the successful large scale synthesis of weinreb amide through a convenient and simple one-flask method via 2-chloro-4,6-dimethoxy-1,3,5-triazine intermediate 20. The syntheses of various classes of hydroxamates and their mode of biological applications have been reviewed. 4 Much of their activities are due to their chelating properties with metal ions, especially with transition metals, hence constituting a very important class of chelating agents with versatile biological activities. The broad biological activities of hydroxamates and the need to improve on their synthetic routes informed the review of their synthesis and biological applications. 5, 6 A number of synthetic routes are available for the preparation of hydroxamic acids, 7-12 but some are tedious, time consuming and costly as well. Colombo, An improved synthesis of the HDAC inhibitorn trichostatin A, Master s Theses and Doctoral Dissertations, Eastern Michigan University, 2009, 1-2. The TBS group was later recovered with tetra- normal-butylammonium fluoride TBAF in THF to give alcohol 28 in 91 yields.
The second portion of the synthesis is presented in schemes 10.
To achieve this, the ester 0.5 M in methanol and hydroxyl amine 10 eq was reacted in the presence of sodium methoxide 1 eq.