Allenic acids specificity

Park, O. and Allen, J.C. 1998. Preparation of phosphopeptides derived from as-casein and (3-casein using immobilized glutamic acid-specific endopeptidase and characterization of their calcium binding. J. Dairy Sci. 81, 2858-2865. 

An increased hydrogen ion concentration, that is a considerably greater amount of acid than the theoretical two equivalents of Scheme 2-1, is necessary in the diazotization of weakly basic amines. The classic example of this is the preparation of 4-nitrobenzenediazonium ions 4-nitroaniline is dissolved in hot 5-10 m HC1 to convert it into the anilinium ion and the solution is either cooled quickly or poured onto ice. In this way the anilinium chloride is precipitated before hydrolysis to the base can occur. On immediate addition of nitrite, smooth diazotization can be obtained. The diazonium salt solution formed should be practically clear and should not become cloudy on standing in the dark. Some practice is necessary, and details can be found in the books emphasizing preparative aspects (Fierz-David and Blangey, 1952 Saunders and Allen, 1985 in Houben-Weyl, Vol. E 16a, Part II, the chapter written by Engel, 1990). These books give a series of detailed prescriptions for specific examples and a useful review of the principal variations of the methods of diazotization. Such reviews have also been written by Putter (1965) and Schank (1975). 

Thai, A. L. V., Coste, E., Allen, J. M., Palmiter, R. D., and Weber, M. J. (1993). Identification of a neuron-specific promoter of human aromatic L-amino acid decarboxylase gene. Mol. Brain. Res 17 227-238. 

In a specific exception to Jones and Kirby s generalization, Tidwell found that the benzylic ester [120] has a shorter C-OX bond [1.457 A (A. D. Allen et al., 1987)] than cyclohexyl p-toluenesulphonate, even though the latter tosylate is solvolysed 200 times more slowly in trifluoroacetic acid. In this... 

Similarly, allenes [32] and alkynols [33] were used as starting materials and their carbonylation provides /3,y-unsaturated acids and unsaturated diacids, respectively. The specific reactivity of alkynols is explained by three formal steps during nickel catalysis (i) carbonylation of the triple bond leading to an acid containing an allylic alcohol moiety (ii) second carbonylation of the double bond to provide a hydroxydiacid and (iii) a dehydration step giving the corresponding unsaturated diacid (Scheme 2). 

Fluorinated carbocations play an important role as intermediates in electrophilic reactions of fluoroolefins and other unsaturated compounds. For example, F-allyl cation 1 was proposed as a reactive intermediate in reactions of HFP with fluoroolefins catalyzed by Lewis acids [7]. The difference in stability of the corresponding allylic cations was suggested as the explanation for regio-specific electrophilic conjugated addition to CF2=CC1CF=CF2 [11]. Allylic polyfluorinated carbocations were proposed as intermediates in the reactions of terminal allenes with HF [53] and BF3 [54], ring-opening reactions of cyclopropanes [55], Carbocations are also an important part of the classic mechanism of electrophilic addition to olefins (see Eq. 2). This section deals with the questions of existence and stability of poly- and perfluorinated carbocations. 

Site-directed mutagenesis has proven to be a very powerful tool for the study of eleetron transfer in the bacterial reaction centre. It has been used to investigate the role played by specific amino acid residues during eleetron transfer, and as a means of modifying the energetics of electron transfer. A number of reviews of the applieation of mutagenesis to study of the bacterial reaction centre have been published (Fyfe et al., 1998 Parson, 1996 Woodbury and Allen, 1995 Takahashi and Wraight, 1994 Kirmaier and Holten, 1993 Coleman and Youvan, 1990). In this section, we concentrate on two heavily-studied elasses of reaction centre mutant that have... 

Bolomey and Allen found that a non-specific phosphatase preparation (Bredereck ) containing a small amount of ribonuclease hydrolyzes ribosenucleic acid in such a manner that guanosine is liberated faster than adenosine, in the early stages of the hydrolysis the equivalent amount of free phosphoric acid is simultaneously formed. After hydrolysis of the purine nucleotide constituents has reached a maximum, hydrolysis of the pyrimidine nucleotides becomes appreciable. (If the ribosenucleic acid is subjected to the action of ribonuclease before treatment with the phosphatase, the reaction is much more rapid.) They therefore tentatively suggested that guanylic acid is the first mononucleotide liberated and adenylic acid the second. Hence, provided that... 

Like the double bond, the carbon-carbon triple bond is susceptible to many of the common addition reactions. In some cases, such as reduction, hydroboration and acid-catalyzed hydration, it is even more reactive. A very efficient method for the protection of the triple bond is found in the alkynedicobalt hexacarbonyl complexes (.e.g. 117 and 118), readily formed by the reaction of the respective alkyne with dicobalt octacarbonyl. In eneynes this complexation is specific for the triple bond. The remaining alkenes can be reduced with diimide or borane as is illustrated for the ethynylation product (116) of 5-dehydro androsterone in Scheme 107. Alkynic alkenes and alcohols complexed in this way show an increased structural stability. This has been used for the construction of a variety of substituted alkynic compounds uncontaminated by allenic isomers (Scheme 107) and in syntheses of insect pheromones. From the protecting cobalt clusters, the parent alkynes can easily be regenerated by treatment with iron(III) nitrate, ammonium cerium nitrate or trimethylamine A -oxide. ° ... 

Another peptide, atrial natriuretic peptide, does not appear to be as specific as oxytocin and somatostatin. Central administration of atrial natriuretic peptide has been shown to attenuate both the increase in water intake caused by water deprivation and the increase in sodium intake caused by sodium depletion (Nakamura, Katsuura, Nakao, Imura, 1985 Tarjan, Denton, Weisinger, 1988 Weisinger, Blair-West, Denton, Tarjan, 1992). Atrial natriuretic peptide, a28-amino acid peptide, audits receptors are distributed widely throughout the brain including many of the areas thought to be involved in body fluid homeostasis (e.g., many of the brain areas that contain ANG II receptors such as the SFO, MnPO, OVLT, and PVN) (Mendelsohn, Allen, Chai, Sexton, Figdor, 1987 Quirion et al.. 1984),... 

When, however, 13(S)-HPOD was incubated with an ammonium sulphate precipitate of defatted com germ, the resulting 12-oxo-PDA was not optically pure but a mixture of enantiomers in a ratio of 82.18 [35]. The 12-oxo-PDA obtained by incubation of 13(S)-HPOT with flaxseed extracts was found to be a racemic mixture [36]. These results may be due to low or absent allene oxide cyclase activity in the preparations used [34]. The allene oxide cyclase, a novel enzyme in the metabolism of oxygenated fatty acids was partially characterised and found to be a soluble protein with an apparent molecular weight of about 45 kDa which catalysed specifically the conversion of allene oxide into 12-oxo-PDA [34]. The allene oxide was very unstable and was rapidly hydrolysed in aqueous media into stable 12-oxo-13-hydroxy-9(z),15(z)-octadecadienoic acid (a-ketols) [34]. 

A new method for the selective demethylation of alkyl methyl phosphates employs a mixture of dimethyl sulphide and methanesulphonic acid. Boron trifluoride etherate catalyses the regio- and stereo-specific alkenylation of phenolic ethers by diisopropyl prenyl or geranyl phosphates (84) in low to moderate yields. 2-(Diethoxyphosphinyl)-1,3-butadienes, e.g., (85), are cleaved by organocopper reagents in some cases this reaction is accompanied by alkylation and rearrangement to an allene structure. ... 

Neutral carbon of organic compounds is inherently a very weak base due to the lack of nonbonding electrons. However, the 7r-system of alkenes, alkynes, and allenes are potential basic sites due to the availability of 7t-electrons. Wooldridge and Roberts [61] first reported the facile photohydration of arylacetylenes to the corresponding ketones (in an overall Markownikoff sense) in dilute aqueous acid solutions. The facile protonation of the excited state was attributed to the enhanced basicity of the alkyne moiety in the excited state, more specifically as a result of extensive charge migration from the aryl group to the acetylene moiety. The photoaddition of methanol [62] and acetic acid to 7c-electron systems such as alkenes, alkynes, and allenes may be rationalized in the same way. 

Furan also undergoes cycloadditions with allenes and even with simpler dienophiles, like acrylonitrile and acrylate (specifically enhanced by the presence of zinc iodide),and with maleate and fumarate esters, if the addition is conducted under high pressure. This device can also be used to increase markedly the reactivity of 2-methoxy- and 2-acetoxyfuran towards dienophiles. Lewis acid catalysis can also been used to accelerate furan Diels-Alder additions. At higher reaction temperatures alkynes and even electron-rich alkenes will add to furan. 

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