Aldehyde-functional study

Up to this point all our attention has been directed toward aldoses carbohydrates hav ing an aldehyde function in their open chain form Aldoses are more common than ketoses and their role m biological processes has been more thoroughly studied Nev ertheless a large number of ketoses are known and several of them are pivotal inter mediates m carbohydrate biosynthesis and metabolism Examples of some ketoses include d nbulose l xylulose and d fructose... 

All the aldehydes hitherto studied, which contain next to the functional aldehydic group one or more labile hydrogen atoms are cap-... 

The reaction of these aldehydes, derived from periodate oxidation, with carbonyl reagents has also been investigated. Studies 147 148 were made on oxidized laminarin, a (1 —> 3)-linked polysaccharide, in which only the terminal residues had been oxidized. The addition of phenylhydrazine acetate detached the remainder of the terminal residue as glyoxal phenyl-osazone. When the aldehydic compounds derived from the periodate oxidation of raffinose and trehalose818a were reacted with p-nitrophenylhydrazine, the authors were surprised to find that one molecule of oxidized raffinose, containing six aldehydic functions, reacts with only three molecules of the reagent, and that the four aldehydic functions of the oxidized trehalose molecule react with only two. The reactions of periodate-oxidized carbo-... 

The effects of benzaldehyde concentrations on turnover frequency are anomalous. Our results indicate that benzaldehyde hydrogenation turnover frequency is independent of benzaldehyde concentration (an apparent zero-order dependence). However, the data in Table 2 indicate otherwise. If the reaction were independent of aldehyde concentration, the rate data should be independent of the type of aldehyde used. This is especially true with p-tolualdehyde and p-anisaldehyde where the structural changes to the aldehyde (addition of p-methyl or p-methoxy) should influence the reactivity of the aldehyde functionality only through electronic effects. Thus, we are forced to conclude that the aldehyde is involved in the rate determining step even though the concentration study does not support its presence. 

Pyridine aldehydes can also be lithiated at C-3, provided that the aldehyde functionality is first converted to its a-aminoalkoxide derivative by reaction with the lithium salt of an amine (90JOC69). In a study with... 

Since ascorbate reduces photooxidation of lipid emulsions and multivitamin preparations (see Figure 4) [19], Lavoie et al. [34] studied the formation of oxidative by-products of vitamin C in multivitamins exposed to light. They found that the loss of ascorbic acid in photoexposed multivitamin preparations was associated with the generation of products other than dehydroascorbate and 2,3-diketogulonic acid, which are the usual products of vitamin C oxidation. The authors showed that hydrogen peroxide at concentrations found in TPN solutions induced the transformation of dehydroascorbate into new, biologically active compounds that had the potential to affect lipid metabolism. They believe that these species have peroxide and aldehyde functions [35]. 

The stereochemistry of the Weinreb-based and phenyl ester based technique has been determined through studying the epimerization of the carbon located a to the aldehyde functional group.135 4 50 Crude products such as Boc-Phe-Val-Ala-H synthesized by both methods contain only one aldehydic peak meaning these techniques are devoid of racemi-zation. However, when the crude products were separated using flash chromatography with 0.1% pyridine as eluant, two aldehydic peaks appeared, which is indicative of some race-mization during separation. 55 4 511 ... 

Pyridylarenes undergo Cu(II)-catalysed diverse oxidative C-H functionalization reactions. The tolerance of alkene, alkoxy, and aldehyde functionality is a synthetically useful feature of this reaction. A radical-cation pathway (Scheme 4) has been postulated to explain the data from mechanistic studies. A single electron transfer (SET) from the aryl ring to the coordinated Cu(II) leading to the cation-radical intermediate is the rate-limiting step. The lack of reactivity of biphenyl led to the suggestion that the coordination of Cu(II) to the pyridine is necessary for the SET process. The observed ortho selectivity is explained by an intramolecular anion transfer from a nitrogen-bound Cu(I) complex.53... 

A density functional study of enantioselectivity in the 2-methylproline-catalysed a-alkylation of aldehydes has been reported.14 On the basis of the computed barriers and transition states, an explanation has been provided for the remarkable and unexpected increase in enantioselectivity that is observed when using 2-methylproline instead of... 

The noncrystalline base, apogeissoschizine (C21H22O2N2, mp of B.HC1, 145°), which is obtained from geissoschizine or from geisso-spermine by the action of concentrated hydrochloric acid, is formed by loss of water and retains the ester and ethylidine functions of the former. The aldehyde function and active hydrogens are absent so that structure XIV seemed a priori very probable (4, 12). This has been confirmed by spectral studies of it and derivatives and by comparison with model compounds containing similar chromophores (7). 

The following advantages of the immobilization using aldehyde-functionalized silanes have been demonstrated in our preliminary study. 

Our measures to overcome these problems include the preparation of aldehyde-functionalized silanes as a new class of spacer molecules for silica surfaces, the application of a series of such compounds with up to three ethoxy groups and different chain length of the anchor group to the surface of controlled pore glass (CPG) as a model substrate, the immobilization of glucose oxidase (GOD) and systematic activity studies over a period of four weeks. 

Since the position of the aldehyde function on the alkyl chain will probably affect the quality of a fixation, we have studied the regioselectivity of the synthesis of aldehyde-functionalized mono- and trialkoxysilanes, using rhodium-hydrido-carbonyl-tris(triphenylphosphine) as catalyst. In general, the hydroformylation of the terminal double bond in organoalkenylsilanes results in the formation of isomeric aldehydes (Eq. 1). 

Substituted cobalt carbonyls of the type Co2(CO)eL2 have also been compared to binary cobalt carbonyls as hydroformylation catalysts for linear aldehydes. One study compared four Co2(CO)6L2 complexes (L = tertiary phosphines with functionalized alkyl groups) to the well-known complexes Co2(CO)6(P n-Bu 3)2 and Co2(CO)8. The bulky phosphine substituent P(CH2CH2CH20CH2CH2)3 showed lower activity than the others, but analogous selectivity. 

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