Regioselectivity phosphates

Regioselective phosphate hydrolysis of 41 and 42 was realized with bifunctional catalysts 43-45, in which one imidazole acts as a base, while the other protonated species acts as an acid (Scheme 13.10) [38]. Whereas all three catalysts were able to hydrolyze 41, only 44 and 45 could cleave 42, and in all cases the maximum... 

Many examples of stereospecific allylation consistent with the above mechanism have been reported. As one example, the regioselective and highly diastereoselective allylation of the lactone 17 with the optically active allylic phosphate 16 proceeded with no appreciable racemization of the allylic part to give the lactones l8 and 19, and the reaction has been used for the synthesis of a polypropionate chain[26]. 

The regioselectivity of a Rhodococcus rhodochrous nitrilase has been demonstrated for the conversion of 5-fluoro-l,3-dicyanobenzene to 5-fluoro-3-cyano-benzoic acid [62]. The nitrilase was expressed in an Escherichia coli transformant, and a cell-free extract was employed as catalyst (0.14wt% cell-free extract) in 0.1m sodium phosphate buffer (pH 7.2) at 25 °C containing 0.18 m 5-fluoro-l,3-dicyanobenzene. After 72 h, the conversion was >98% and the reaction was stopped by addition of phosphoric acid (pH 2.4) to yield 5-fluoro-3-cyano-benzoic acid as a crystalline product (97% isolated yield). 

A highly useful and important regioselective reduction of substrate 84 leads to a mixture of 3-hydroxy ethers 85 and 86 in a 32 1 ratio (Eq. 306). Compound 85 is further converted to the anti-influenza drug oseltamivir phosphate, better known as Tamiflu .498... 

Even more interesting is the observed regioselectivity of 37 its reaction with 2, 3 -cCMP and 2, 3 -cUMP resulted in formation of more than 90% of 2 -phosphate (3 -OH) isomer. The postulated mechanisms for 37 consists of a double Lewis-acid activation, while the metal-bound hydroxide and water act as nucleophilic catalyst and general acid, respectively (see 39). The substrate-ligand interaction probably favors only one of the depicted substrate orientations, which may be responsible for the observed regioselectivity. Complex 38 may operate in a similar way but with single Lewis-acid activation, which would explain the lower bimetallic cooperativity and the lack of regioselectivity. Both proposed mechanisms show similarities to that of the native phospho-monoesterases (37 protein phosphatase 1 and fructose 1,6-diphosphatase, 38 purple acid phosphatase). 

A comparable metabolic fate is documented for the hydraulic fluid tributyl phosphate. Following administration to rats, the Bu groups were oxidized to alcoholic, ketonic, and acidic metabolites. The oxidized Bu groups were then cleaved by enzymatic hydrolysis [103], With 2-ethylhexyl diphenyl phosphate (9.48), an interesting case of regioselectivity was noted during its in vivo metabolism in rats. Indeed, this flame retardant and plasticizer was... 

It has been established" that the leaves of Liriodendron tulipifera convert 1-deoxy-D-xylulose (285) into 2-C-methyl-D-erythritol (286) via a skeletal rearrangement (see Scheme 90) reminiscent of the formation of terpene precursors from 1-deoxy-D-xylulose 4-phosphate. An esterase-catalysed regioselective 6-deacylation of... 

A combination of rhodium complexes and phosphates promotes a highly regioselective allylic alkylation of unsym-metric allylic esters, where alkylation occurs at the more substituted allylic terminus of the esters (Equation (46)). As Evans and his co-workers reported, both the regio- and stereochemistry of the starting allylic esters are maintained in the allylic alkylated products (Equation (47)). Thus, the rhodium-catalyzed allylic alkylation takes place at the carbon substituted by a leaving group with net retention of configuration. A variety of carbon-centered... 

As described in many reviews, Trost and his co-workers have carried out a pioneering work on the molybdenum-and tungsten-catalyzed allylic alkylation of allylic esters regioselectivity of the reaction is often complementary to the palladium-catalyzed allylic alkylation. The first asymmetric version was disclosed by Pfaltz and Lloyd-Jones in 1995 (Equation (63)). They used a catalytic amount of a novel tungsten complex, prepared from [W(CO)3(MeCN)3] or [W(cycloheptatriene) (COIs] and optically active (diphenylphosphino)phenyloxazolines 57, for the allylic alkylation of 3-aryl-2-propenyl phosphate with dimethyl sodiomalonate to isolate the corresponding branched alkylated compounds as a major isomer with an excellent enantioselectivity (96% ee). Unexpectedly, 3-aryl-2-propenyl carbonates are shown to be unreactive. It is worth noting that an isostructural molybdenum complex does not promote the catalytic alkylation under the same reaction conditions. In contrast, Lloyd-Jones and Lehmann reported the stereocontrolled... 

Kost, D. M., Gerdt, J. P., Pradeepkumar, P. I., and Silverman, S. K. (2008). Controlling regioselectivity and site-selectivity in RNA ligation by Zn2+-dependent deoxyribozymes that use 2,3,-cyclic phosphate RNA substrates. Org. Biomol. Chem. 6, 4391—4398. 

Lo HC, Leiva C, Buriez O, Kerr JB, Olmstead MM, Fish RH (2001) Bioorganometallic chemistry. 13. Regioselective reduction of NAD+ models, 1-benzylnicotinamide triflate and P-nicotinamide ribose-5 -methyl phosphate, with in situ generated [CpRh(Bpy)H]+ structure-activity relationships, kinetics, and mechanistic aspects in the formation of the 1,4-NADH derivatives. Inorg Chem 40 6705-6716... 

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