Phosphate buffer synthesis

A detailed procedure for the use of MCPBA recently appeared in Reagents for Organic Synthesis by Fieser and Fieser. The commercially available MCPBA (Aldrich) is 85% pure the contaminant, m-chlorobenzoic acid, can be removed by washing with a phosphate buffer of pH 7.5. The epoxidation is usually performed as follows a solution of 3 -acetoxy-5a-androst-16-ene (2.06 g, 6.53 mmoles) in 25 ml of chloroform (or methylene dichloride) is chilled to 0° in a flask fitted with a condenser and drierite tube and treated with a solution of commercial MCPBA (1.74 g, 20% excess) in 25 ml chloroform precooled to the same temperature. The mixture is stirred and allowed to warm to room temperature. After 23 hr (or until TLC shows reaction is complete) the solution is diluted with 100 ml chloroform and washed in sequence with 100 ml of 10% sodium sulfite or sodium iodide followed by sodium thiosulfate, 200 ml of 1 M sodium bicarbonate and 200 ml water. The chloroform extract is dried (MgS04) and evaporated in vacuo to a volume of ca. 10 ml. Addition of methanol (10 ml) followed by cooling of the mixture to —10° yields 0.8 gof 16a,17a-epoxide mp 109.5-110°. Additional product can be obtained by concentration of the mother liquor (total yield 80-90%). 

TheNef reaction of primary nitro compounds gives iildehydes or carboxylic acids, depending on the reaction conditions. Each transformation provides an important tool in organic synthesis. Primary nitro compotmds are converted into carboxylic acids vrith concentrated mineriil acids. Because such harsh conditions iilso lead to side reactions, a milder method is required inorganic synthesis. Basic phosphate-buffered KMnO rapidly converts primary nitroalkanes into carboxylic acids in 90-99% yield fEq. 6.13. "... 

The melting point Tm and kinetics are independent of pH and of the salt concentration. This was found by studies in 1% aqueous acetic acid, pH 3.0 as well as in 50 mM phosphate buffer, pH 7.5). Recently, Greiche and Heidemann23 described the synthesis... 

Oxidation of phenyl hexyl sulphide with sodium metaperiodate gave also only a trace amount of the corresponding sulphoxide72. On the other hand, Hall and coworkers73 prepared benzylpenicillin and phenoxymethyl penicillin sulphoxides from the corresponding benzyl esters by oxidation with sodium metaperiodate in dioxane solution with a phosphate buffer. A general procedure for the synthesis of penicillin sulphoxides was reported later by Essery and coworkers74 which consists in the direct oxidation of penicillins or their salts with sodium metaperiodate in aqueous solution at pH 6.5-7.0. 1-Butadienyl phenyl sulphoxide 4475 and a-phosphoryl sulphoxides 4576 were also prepared by the same procedure. 

The antiviral agent virantmycin is an unusual chlorinated tetrahydroquinoline isolated from a strain of Streptomyces (Figure 6.10). Hydrolysis of a prochiral 2,2-disubstituted dimethyl malonate with PLE in DMSO-pH 8 phosphate buffer (1 4) was a key step in a stereodivergent synthesis of this natural product [57]. 

A divergent synthesis of tropane alkaloid ferruginine was reported by Node and coworkers [59]. The P-ketoester intermediate was prepared by a novel PLE-catalyzed asymmetric dealkoxycarbonylation (hydrolysis followed by a decarboxylation) of a symmetric tropinone-type diester (Figure 6.12). Dimethyl sulfoxide was added to the phosphate buffer pH 8 (1 9) to reduce the activity of PLE and prevent over-deal-koxycarbonylation leading to tropinone. 

In 2001, researchers at Wyeth-Ayerst described the preparation of RFI-641, a potent and selective inhibitor of the respiratory syncytial virus (RSV) [251], The final key step in the synthesis involved the coupling of a diaminobiphenyl with two equivalents of a chlorotriazine derivative under microwave irradiation (Scheme 6.123). The reaction was carried out in dimethyl sulfoxide/phosphate buffer/sodium hydroxide in an open vessel at 105 °C. This protocol provided RFI-641 in 10% isolated yield. 

Aminoethyl)piperidine (16) is a base and nucleophile employed for removal of fluorenylmethyl-based protectors during synthesis in solution. The adduct formed with the released moiety can be separated from the peptide ester by extraction into a pH 7.4 phosphate buffer (see Section 7.11). 

Table 2 Synthesis of phenazine ethers 10,44a-g by etherification of 2-hydroxyphenazine (9) with ROMs(-Br) and their redox potentials vs. SHE as determined by cyclic voltammetry in phosphate buffer at pH 7 using HMDE...

Preparative fractionation of lOOmg sample of HPD and the product of the DP-HP synthesis were carried out on a 5x30cm Sephadex LH-20 column (Pharmacia, Piscataway, NJ.). The porphyrin components were first dissolved in 40ml of tetrahydrofuran-methanol-5mM aqueous phosphate buffer, pH 7, (2 1 1), and subsequently eluted with the same solvent. The use of this methodology for the isolation of the tumor-localizing fraction of HPD from other porphyrin components present in the drug mixture has been discussed in detail in the literature.(11) The component of HPD which elutes very close to the void volume of the LH-20 column has been characterized as the tumor-localizing fraction of HPD. 

Hydroxynitrile lyase Synthesis of (R)-mandelonitrile in sodium phosphate buffer/methyl tert-butyl ether [70]... 

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