Hydroxy adds acylation

Using the syringe from step 30, add THF (15 mL) to the flask containing the methylated 8-hydroxy iron acyl complex. 

Chiral acyliminiums were used for the preparation of enantiopure piperidines [267]. Recently, the use of enantio-enriched y-alkoxyallyltins onto chiral acyl iminiums [268] provided a new entry into the synthesis of potential precursors of a-amino-/3-hydroxy adds or aminosugars, with a total control of the stereochemistry. 

It is possible to add an acyl group to a ketone to give (after hydrolysis) an a-hydroxy ketone. This can be done by adding RLi and CO to the ketone at... 

To eliminate acylation products at tyrosine residues, add 1 pi of 15 M hydroxy-lamine solution in water to each protein sample and incubate for 30 minutes at 37°C (Zappacosta et al., 2006). 

The antibiotic viscosin from Pseudomonas viscosa (Scheme 8) is a cyclo-depsipeptide acyl-ated at the N-terminus with D-3-hydroxydecanoic add.[103 112] The C-terminal carboxy group is esterified with the hydroxy group of the Thr3 residue. The synthesis of this natural product presents the problem of an ester ring closure and was performed in two steps with initial solid-phase synthesis of the Thr3-0-branched linear intermediate followed by ring closure with formation of the amide bond.1 131... 

Despite this versatility, cyanide adds only one carbon atom of course and we need other more general acyl anion equivalents. In chapter 16 we saw how acetylenes can give rise to ketones by hydration. A very simple example is the hydroxy-ketone 11 that could come from the acetylenic alcohol 12 by hydration and hence from acetone with the anion of acetylene acting as the acyl anion equivalent. 

Deracemization of mandelic add with the combined action of two enzymes has been reported. rac-MandeUc acid is acylated by a Pseudomonas sp. lipase in diisopropyl ether. After solvent removal the mfacture of mandeUc acid enriched in the R-form and the 0-acetyl derivative of the S-configuration are subjected to the mandelate racemase-catalyzed racemization in aqueous buffer. In these conditions only the non-acetylated hydroxy acid is racemized. In order to obtain (S)-0-acetylmandelic acid in an 80% isolated yield and a >98% e.e. the process must be repeated four times [9]. 

Cottjugate addition of water. The a,0 unsaturated acyl CoA produced in step 1 reacts with water by a conjugate addition pathway Spction 19.M) to yk ld a fJ-hydroxy acyl CoA in a process catalyzed by the enzyme eftoyl CoA hydratose. Water as nucleophile add to fi carbon of the douUe bond, yielding an enolate ion intermediate, whi[Pg.1198]

Nucleophilic addition of LiR or H , from Li[BEt3H], to (14) occurs at the cis-CO to give acyl or formyl anions [Re C(0)R X(C0)4] , which may be protonated or alkylated to give the corresponding Fischer carbenes [Re C(OR0R X(CO)4]. In contrast to the dinuclear formyls [Re2(CO)9(CHO)], these are not stabilized by SnBu3pI because rapid X loss produces Re(CO)4(CHO), which decomposes to ReH(CO)5 or oxidatively adds the Sn-H bond. Remarkably, double nucleophilic alkylation is possible without X replacement, and upon protonation bis(hydroxy)carbene complexes, for example, fac-[ReX C(OH)Me 2(CO)3] are obtained. ... 

Classically, the acylzirconocene chlorides can be converted into aldehydes, carboxyhc acids, esters, and acyl halides. Recently, the usefulness of acylzirconocenes has been extended. In fact, these unmasked acyl anions directly add to aldehydes and imines affording a-hydroxy or a-amino ketones, respectively. The reaction of acylzirconocene chlorides with imines also proceeds under Bronsted acid-catalyzed conditions, even with aqneons acids. ... 

Threonine contains a sterically hindered and therefore less reactive hydroxy group. The O-acylation of unprotected threonine during coupling reactions is therefore less problematic, but can nevertheless occur. Noncoded hydroxy amino acids containing a secondary hydroxy group have a reactivity similar to threonine. These hydroxy amino adds contain an additional asymmetric center at the (3-carbon atom. In the case of reactions on the secondary hydroxy group, this center is accessible to racemization, e.g. threonine can be converted into allo-threonine. 

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