Preparation moiety

Figure Bl.22.10. Carbon K-edge near-edge x-ray absorption (NEXAFS) speetra as a fiinotion of photon ineidenee angle from a submonolayer of vinyl moieties adsorbed on Ni(lOO) (prepared by dosing 0.2 1 of ethylene on that surfaee at 180 K). Several eleetronie transitions are identified in these speetra, to both the pi (284 and 286 eV) and the sigma (>292 eV) imoeeupied levels of the moleeule. The relative variations in the intensities of those peaks with ineidenee angle ean be easily eonverted into adsorption geometry data the vinyl plane was found in this ease to be at a tilt angle of about 65° from the surfaee [71], Similar geometrieal detenninations using NEXAFS have been earried out for a number of simple adsorbate systems over the past few deeades.

In the total synthesis of zearaienone (451), the ester 450 was prepared by the carbonylation of the crowded aryl iodide 448. The alkyl iodide moiety in the alcohol molecule 449 is not attacked[306]. Methyl trifluoromethacrylate (453) was prepared by the carbonylation of 3,3,3-trifluoro-2-bromopropylcne (452), The carbonylation in the presence of alkylurea affords 454. which is converted into the trifluoromethyluracil 455[307],... 

Allylic metal compounds useful for further transformations can be prepared by Pd-catalyzed reactions of allylic compounds with bimetallic reagents. By this transformation, umpolung of nucleophilic 7r-allylpalladium complexes to electrophilic allylmetal species can be accomplished. Transfer of an allyl moiety from Pd to Sn is a typical umpolung. 

The key step in the total synthesis of rhizobitoxine is the Pd-catalyzed exchange reaction of the methyl alkenyl ether moiety in 4 with the functionalized alcohol, although the yield is low[3]. The enol pyruvate 6 (a-ethoxyacrylic acid) is prepared by the reaction of methyl a-methoxyacrylate or a-methoxy-acrylic acid (5) with ethanol catalyzed by PdCl2(PhCN)2 at room temperature in the presence of CuCli and NaH2P04[4],... 

Fluorinated diacids offer a convenient method for introducing a perfluoro moiety into organic molecules. They are of potential interest in the preparation of polyamides and other fluorinated polymers. A detailed description of the perfluorocarboxyUc acids and their derivatives has been pubflshed (1), and a review article on polyfluorinated linear biflmctional compounds has appeared (35). 

Hydrazides and Related Compounds. Substitutioa of the hydroxyl group ia carboxyhc acids with a hydraziao moiety gives carboxyhc acid hydrazides. la this formal sease, a number of related compouads faU within this product class although they are aot aecessatily prepared this way. Table 5 lists some of the more common of these compouads (82). 

Transesterification of methyl methacrylate with the appropriate alcohol is often the preferred method of preparing higher alkyl and functional methacrylates. The reaction is driven to completion by the use of excess methyl methacrylate and by removal of the methyl methacrylate—methanol a2eotrope. A variety of catalysts have been used, including acids and bases and transition-metal compounds such as dialkjitin oxides (57), titanium(IV) alkoxides (58), and zirconium acetoacetate (59). The use of the transition-metal catalysts allows reaction under nearly neutral conditions and is therefore more tolerant of sensitive functionality in the ester alcohol moiety. In addition, transition-metal catalysts often exhibit higher selectivities than acidic catalysts, particularly with respect to by-product ether formation. 

Such copolymers of oxygen have been prepared from styrene, a-methylstyrene, indene, ketenes, butadiene, isoprene, l,l-diphen5iethylene, methyl methacrjiate, methyl acrylate, acrylonitrile, and vinyl chloride (44,66,109). 1,3-Dienes, such as butadiene, yield randomly distributed 1,2- and 1,4-copolymers. Oxygen pressure and olefin stmcture are important factors in these reactions for example, other products, eg, carbonyl compounds, epoxides, etc, can form at low oxygen pressures. Polymers possessing dialkyl peroxide moieties in the polymer backbone have also been prepared by base-catalyzed condensations of di(hydroxy-/ f2 -alkyl) peroxides with dibasic acid chlorides or bis(chloroformates) (110). 

NitrofuraZone. 2-[5-Nitro-2-furanyl)methylene]hydrazinecarboximide, the first nitrofiiran to be employed clinically, is prepared from 5-nitro-2-furancarboxaldehyde and semicarbazide (19). This product has seen clinical use topically as an antibacterial, for systemic appHcation for bacterial infections in poultry and swine, and also has been employed as a food additive. In rats, nitrofurazone is hydroxylated at the 4 position of the furan moiety (27). The involvement of nitrenium ions has also been postulated in the mechanism of action of nitrofurazone (38). 

Derivatives Containing a Modified 4,6-Disubstituted-2-deoxystreptamine Moiety. Mutasynthesis is the term used to refer to the process of employing mutated intermediate-requiring organisms to prepare derivatives that would be difficult to obtain by synthetic or semisynthetic means (117,185—188). Whereas this approach has been used to obtain amiaoglycoside analogues, the primary contribution has been as a means to vary the 2-deoxystreptamiae portion of the molecule. The most significant compound found by this approach is 5-episisomicin, which is produced by a... 

Kits. Kits for the preparation of radiopharmaceuticals are a convenient solution to synthesis of products containing short-Hved radionucHdes (eg, In, I, Tc) bound to a nonradio active moiety. The labeling step is performed either at a commercial radiopharmacy, or within the institutional nuclear medicine laboratory. The kits are usually stored as a frozen solution or lyophilized product. The material of interest is then metered out into kit dosages. The kit vials are thawed or reconstituted and mixed with the appropriate radionucHde. 

Reactions. Although carbapenems are extremely sensitive to many reaction conditions, a wide variety of chemical modifications have been carried out. Many derivatives of the amino, hydroxy, and carboxy group of thienamycin (2) have been prepared primarily to study stmcture—activity relationships (24). The most interesting class of A/-derivatives are the amidines which are usually obtained in good yield by reaction of thienamycin with an imidate ester at pH 8.3. Introduction of this basic but less nucleophilic moiety maintains or improves the potency of the natural material while greatiy increasing the chemical stabiUty. Thus /V-formimidoyl thienamycin [64221-86-9] (MK 0787) (18), C 2H yN204S, (25) was chosen for clinical evaluation and... 

Preparation of (14) and treatment with A[,A[-bis(ttimethylsily)fomiamide (BSF) and triethylamine provided (16) in 84% yield via the putative imine intermediate (15). The trifliioromethyl group could be replaced by other moieties such as 2,4,5 trichlorophenyl, pentafluorophenyl, or nonafluorobutyl with increasing effectiveness. 

The 3, 5 -cyclic phosphate of ara-C has shown significant antiviral activity in vivo with an efficacy greater than that exhibited by ara-C itself (35). It was speculated that the 3, 5 -cycHc phosphate moiety may inhibit the deamination of ara-C, thus causiag the iacreased in vivo potency. A number of derivatives of ara-C have been prepared ia an effort to improve on antiviral activity and to reduce the toxicity. One such derivative is 2 - uoro-5-iodo-l-p-D-arabiQofuranosylcytosiae [69123-90-6] (FIAC, 17), synthesized (36) ia 1979. It is active against certain DNA vimses. FIAC,... 

Mixed cellulose esters containing the dicarboxylate moiety, eg, cellulose acetate phthalate, have commercially useful properties such as alkaline solubihty and excellent film-forming characteristics. These esters can be prepared by the reaction of hydrolyzed cellulose acetate with a dicarboxyhc anhydride in a pyridine or, preferably, an acetic acid solvent with sodium acetate catalyst. Cellulose acetate phthalate [9004-38-0] for pharmaceutical and photographic uses is produced commercially via the acetic acid—sodium acetate method. 

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