Branched-chain preparation

Dyes with Branched Chains. Symmetrical triaucleai dyes with the shortest chain branches, [l.l.l]tetramethines (37), have been prepared by reaction of the corresponding heterocycHc bases with tetrachloro- or tetrabromomethane (33). 

In Parenteral and Enteral Nutrition. Amino acid transfusion has been widely used since early times to maintain basic nitrogen metaboHsm when proteinaceous food caimot be eaten. It was very difficult to prepare a pyrogen-free transfusion from protein hydrolysates. Since the advances in L-amino acid production, the crystalline L-amino acids have been used and the problem of pyrogen in transfusion has been solved. The formulation of amino acid transfusion has been extensively investigated, and a solution or mixture in which the ratio between essential and nonessential amino acid is 1 1, has been widespread clinically. Special amino acid mixtures (eg, branched chain amino acids-enriched solution) have been developed for the treatment of several diseases (93). 

Cyanohydrin Synthesis. Another synthetically useful enzyme that catalyzes carbon—carbon bond formation is oxynitnlase (EC 4.1.2.10). This enzyme catalyzes the addition of cyanides to various aldehydes that may come either in the form of hydrogen cyanide or acetone cyanohydrin (152—158) (Fig. 7). The reaction constitutes a convenient route for the preparation of a-hydroxy acids and P-amino alcohols. Acetone cyanohydrin [75-86-5] can also be used as the cyanide carrier, and is considered to be superior since it does not involve hazardous gaseous HCN and also virtually eliminates the spontaneous nonenzymatic reaction. (R)-oxynitrilase accepts aromatic (97a,b), straight- (97c,e), and branched-chain aUphatic aldehydes, converting them to (R)-cyanohydrins in very good yields and high enantiomeric purity (Table 10). 

These structures occur in branched chains of low DP. Particularly interesting is unit 24 which predominates in polymers prepared at —20 °C with trifluoroacetic acid these products are in fact phantom polymers108 in which everything seems to have gone the wrong way. 

Clear, surface-active phosphate ester compositions were prepared by heating 1 mol P4O,0 with 2-4.5 mol of a linear or branched chain C6, 8 saturated alcohol, a C4 20 mono- or dialkylphenol, or a 2- to 14-mol ethylene oxide adduct of one of these alcohols or alkylphenols at 25-110°C, and hydrolyzing the reaction product at 60-110°C with 0.5-3.0% H20. The hydrolyzed mixture had a lower Klett color value than the phosphorylation reaction mixture [21]. 

It is used to prepare symmetrical RR, where R is straight or branched chained, except that little or no yield is obtained when there is a branching. The reaction is not successful for R = aryl. Many functional groups may be present, though many others inhibit the reaction." Unsymmetrical RR have been made by coupling mixtures of acid salts. 

Two branched-chain sugars, methyl 3-azido-4,6-0-benzylidene-2,3,-dideoxy-3-C-(fluoromethyl)-a-D-flraZ)/ o-hexopyranoside and methyl 2-azido-4,6-0-benzylidene-2,3-dideoxy-2-C-(fluoromethyl)-) -D-r/to-hexo-pyranoside have been prepared through the usual displacement reactions. 

David, S. and Lepine, M.-C., Preparation of sugars with branched chains, a methylene bridge, or C-l-phenyl substituents by the Ramirez dioxaphosphole condensation, /. Chem. Soc., Perkin l, 1262, 1980. 

Henry reaction of nitro sugar 11 with formaldehyde allowed the introduction of two hydroxymethyl groups at the carbon bearing the nitro group, and hence opened a specific route for the preparation of branched-chain imino sugar 57 and analogues (Scheme 20).44... 

Finally, when L-sorbose (81) was treated with hydrogen cyanide, a branched-chain, sugar lactone was formed which was characterized by converting it into a diacetal.127 An X-ray structure determination of this material revealed it to be 2,21 5,6-di-0-isopropylidene-[2-C-(hy-droxymethyl)-L-gulono-l,4-lactone] (82). However, all subsequent efforts to prepare 82 resulted in the formation of 2,3 5,6-di-0-isopropyli-dene-2-C-(hydroxymethyl)-L-gulono-l,4-lactone (83). 

Unsaturated branched-chain sugars were synthetized with 72-84 % yield from both protected and unprotected 2-bromo-D-glucal with methyl acrylate in CH3CN/H2O 5/1 or in DMF/H2O 5/1 with a catalyst prepared from [Pd(DBA)2] and P(o-tolyl)3. Et3N or K2CO3 + /1-BU4NHSO4 could be used as base with similar results. 

This review presents an evaluation of the experimental material available to illustrate the scope and limitations of the dialdehyde-nitro-alkane cyclization and its preparative utility as a synthetic entry to branched chain aminocyclanols and aminosugars. 

A useful application of the chemistry shown in Scheme 83 is the synthesis of branched-chain functionalized carbohydrates. For this purpose two epoxides 261 and 262 derived from D-glucose and 263 derived from D-fructose were prepared following reported methodologies, and were submitted to a DTBB-catalyzed lithiation as described above in Scheme 83. The expected intermediates 264-266 and final products 267-269 were prepared in a regio- and stereoselective manner in 15- 95% yield" Also here, the use of a prochiral electrophile gave equimolecular amounts of both diastereomers. 

Note 2 Semi-interpenetrating polymer networks may be further described by the process by which they are synthesized. When an SIPN is prepared by a process in which the second component polymer is formed or incorporated following the completion of formation of the first component polymer, the SIPN may be referred to as a sequential SIPN. When an SIPN is prepared by a process in which both component polymers are formed concurrently, the SIPN may be referred to as a simultaneous SIPN. (This note has been changed from that which appears in ref [4] to allow for the possibility that a linear or branched polymer may be incorporated into a network by means other than polymerization, e.g., by swelling of the network and subsequent diffusion of the linear or branched chain into the network.). 

Several F-labeled fatty acid derivatives have been successfully prepared and evaluated as potential FAO assessing tracers [19-24]. Methyl-branched-chain (w- F-fluorofatty acids, such as 3-methyl-(3-MFHA) and 5-methyl-17-[ F]fluoro-heptadecanoic acid (5-MFHA), have been reported [23]. In a comparative study, it was found that rw-[ F]fluoropalmitic acid (FPA) exhibits the highest myocardial uptake, followed by 5-MFHA and 3-MFHA. FPA possesses the fastest myocardial washout rate, and 3-MFHA the slowest. In lipid analysis studies, 5-MFHA... 

---