Hydroxylation stereoselective

STEREOSELECTIVE HYDROXYLATION WITH THALLIUM(I) ACETATE AND IODINE trans- AND cis-l,2-CYCLOHEXANEDIOLS... 

Analogously, for preparation of racemic carba-a-glucopyranose 49 from 52, esterification of (—)-52 furnished the ester 95, which was transformed into compound 96 by debromination with zinc dust and acetic acid. Stereoselective hydroxylation of 96 with osmium tetraoxide and hydrogen peroxide, followed by acetylation, gave compound 97. Lithium aluminum hydride reduction of 97, and acetylation of the product, gave pentaacetate 98, which was converted into 99 by hydrolysis. ... 

Recently, Breslow19 reported a regioselective and stereoselective hydroxylation of steroid substrates catalyzed by manganese porphyrin... 

Resting cells of bacterium Stenotrophomonas maltophilia CGMCC 1.1788 catalyze the stereoselective hydroxylation at position C12 of imidacloprid (IMl) in the imidazolidine ring to form (R)-5-hydroxy IML Under acidic conditions, 5-hydroxy IMI is converted into olefin IMl (Figure 12.2), which exhibits about 19 times more insecticidal efficacy than IMI against horsebean aphid imago. 

The procedure is very easy to reproduce and the stereoselective hydroxylation of IMI with S. maltophilia CGMCC 1.1788 may be applied to some other neonicotinoid insecticides, such as thiacloprid (Table 12.1). 

Mamiya K, leiri I, Shimamoto J, Yukawa E, Imai J, Ni-nomiya H et al. The effects of genetic polymorphims of CYP2C9 and CYP2C19 on phenytoin metabohsm in Japanese adult patients with epilepsy studies in stereoselective hydroxylation and population pharmacokinetics. Epilepsia 1998 29(12) 1317-23. 

In every case the information provided has been obtained by collating public domain sources of information, but unfortunately very often little data is available, particularly on commercial aspects, even for products that have proved to be big successes. Thus microbial biotransformations for steroid modification, particularly stereoselective hydroxylations, such as the use of Rhizopus arrhizus to convert progesterone into antiinflammatory and other dmgs via 11- -hydroxyprogestrone, have proved to be very successful. However, comparatively little useful information exists from public domain sources, despite (or perhaps because) a market of hundreds of millions /a exists for such microbially transformed steroids (cortisone, aldosterone, prednisolone and prednisone etc.) produced by microbial hydroxylation and dehydrogenation reactions coupled with complimentary chemical steps. 

Spiro acetals can also be stereoselectively hydroxylated, in high yield, with osmium tetraoxide and a catalyst. The resultant diol is formed by. vyw-hydroxylation from the least hindered side of the alkene moiety (equation 21)121. 

A feature of some pterocarpan phytoalexins (e.g., pisatin and glyceollin of pea and soybean, respectively) is their hydroxylation at position 6a, a reaction catalyzed by a microsomal cytochrome P450 monooxygenase.49 50 A cDNA encoding this enzyme was recently characterized from elicited soybean cell cultures.51 The microsomal protein, expressed in yeast cells, catalyzed the stereoselective hydroxylation of (6a/ , lla/ )-3,9-dihydroxypterocarpan to its 6a-hydroxy derivative. It was also demonstrated that the enzyme expression is regulated at the transcriptional level.51... 

Muenzer, D. F, Meinhold, P, Peters, M. W., Feichtenhofer, S., Griengl, H., Arnold, F H., Gheder, A., and De Raadt, A. 2005. Stereoselective hydroxylation of an achiral cyclopentanecarboxylic acid derivative using engineered P450s BM-3. Chem. Comm., 20, 2597-2599. 

The discovery of this stereoselective hydroxylation at C-11 and the introduction of diosgenin as a cheap raw material had dramatic effects in reducing the cost of steroid hormones. Thus in the early 1950 s, the price of progesterone dropped within just three years from 80 to 3/g. In its turn cortisone cost about 200/g in 1949 whereas today its cost is less than l/g. Several other steroids are also prepared by processes which include a microbiological oxidation step among them, cortexone and fluocortolone. 

This reagent is particularly useful for stereoselective hydroxylation. Thus the lactone 2 is oxidized by 1 to a single produet (3), whereas oxidation with MoOPH results in a mixture of 3 and the cpimer 4. 

Microaganisms have the ability to effect chemical oxidations on a wide variety of substrates, many of which occur with chemo-, regio- or steieo-selectivities unattainable by conventional chemical methods. This is paiticulariy true in the case of unactivated C—H oxidation. What chemical oxidation system, for example, would be c )iable of the stereoselective hydroxylation of the diol (1) to the 3P-hydioxy derivative (2) This transformation has been reported to occur in 80% yield when a microbial oxidation is employed. ... 

Milbemycin derivatives can be stereoselectively hydroxylated at the allylic 13p-position by a variety of microorganisms including Streptomyces violascens (ATCC 31560), Streptomyces carbophilus (FERM BP-1145) or Streptomyces diastatochromogenes (ATCC 31561), and in preparatively useful yields. ... 

A number of additional methods are available. Among die most useful is the angular hydroxylation by benzeneseleninic anhydride. Oxidation of primary or secondary a-centers produces ot,p-unsaturated ketones, but where the a-center is tertiary, stereoselective hydroxylation is possible, e.g. (20). The initially formed seleno enolate undergoes 2,3-sigmatropic rearrangement and subsequent hydrolysis reveals the a-hydroxy ketone in good yield. 

Chiba, K. Role of CYP2C19 in stereoselective hydroxylation of mephobarbital by human liver microsomes. Drug Metab. Disp. 2001, 29, 36 0. 

Stereoselective hydroxylation at C(5) has been achieved from the corresponding 3-amino-derivatives by neighbouring-group participation. A possible mechanism involving a dihydro-oxazinium cyclic intermediate has been proposed. 

Thallium monoacetate, TIOCOCH3 (hygroscopic), behaves similarly to silver acetate or silver benzoate. In the presence of iodine, it accomplishes stereoselective hydroxylations of alkenes [410]. 

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