Two sequential

Hydroxy butyrate dehydrogenase (from Rhodopseudomonas spheroides) [9028-38-0] Mf 85,000, [EC 1.1.1.30], amorphous. Purified by two sequential chromatography steps on two triazine dye-Sepharose matrices. [Scavan et al. Biochem J 203 699 7952.]... 

Figure 2.21 Two sequentially adjacent hairpin motifs can be arranged in 24 different ways into a p sheet of four strands, (a) Topology diagrams for those arrangements that were found in a survey of all known structures in 1991. The Greek key motifs in (1) and (v) occurred 74 times, whereas the arrangement shown in (viii) occurred only once, (b) Topology diagrams for those 16 arrangements that did not occur in any structure known at that time. Most of these arrangements contain a pair of adjacent parallel P strands.

Figure 4.6 The bifunctional enzyme PRA-isomerase (PRAI) IGP-synthase (IGPS) catalyzes two sequential reactions in the biosynthesis of tryptophan. In the first reaction (top half), which is catalyzed by the C-terminal PRAI domain of the enzyme, the substrate N-(5 -phosphoribosyl) anthranilate (PRA) is converted to l-(o-carboxyphenylamino)-l-deoxyribulose 5-phosphate (CdRP) by a rearrangement reaction. The succeeding step (bottom half), a ring closure reaction from CdRP to indole-3-glycerol phosphate (IGP), is catalyzed by the N-terminal IGPS domain.

Classify the following reactions as electrocyclizations, sigmatropic rearrangements, cycloadditions, etc., and give the correct symbolism for the electrons involved in each concerted process. Some of the reactions proceed by two sequential processes. 

Vertessy, B. G., Orosz, F., Kovacs, J., and Ovadi, J., 1997. Alternative binding of two sequential glycolytic enzymes to microtnbnles. Molecnlar studies in the phosphofrnctokinase/aldolase/microtnbnle Journal of... 

The above integral screening is even more advantageous if the Fock matrix is formed incrementally. Consider two sequential density and Fock matrices in the iterative procedure (eq. (3.52)). 

Diaryl bisfurans are available from two sequential Paal-Knorr reactions of tetraketones. For example, Barba converted 46 into 3,3"-bis-2,5-diphenylfuran (47) in good yield upon treatment with sulfuric acid and acetic anhydride. ... 

Ester hydrolysis is common in biological chemistry, particularly in the digestion of dietary fats and oils. We ll save a complete discussion of the mechanistic details of fat hydrolysis until Section 29.2 but will note for now that the reaction is catalyzed by various lipase enzymes and involves two sequential nucleophilic acyl substitution reactions. The first is a trcinsesterificatiori reaction in which an alcohol gioup on the lipase adds to an ester linkage in the tat molecule to give a tetrahedral intermediate that expels alcohol and forms an acyl... 

The metabolic breakdown of triacylglycerols begins with their hydrolysis to yield glycerol plus fatty acids. The reaction is catalyzed by a lipase, whose mechanism of action is shown in Figure 29.2. The active site of the enzyme contains a catalytic triad of aspartic acid, histidine, and serine residues, which act cooperatively to provide the necessary acid and base catalysis for the individual steps. Hydrolysis is accomplished by two sequential nucleophilic acyl substitution reactions, one that covalently binds an acyl group to the side chain -OH of a serine residue on the enzyme and a second that frees the fatty acid from the enzyme. 

Problem 30.9 When a 2,6-disubslituted allyl phenyl ether is heated in an attempted Claisen rearrangement, migration occurs to give the />-allyl product as the result of two sequential pericyclic reactions. Explain. 

Two sequential pericyclic reactions are involved in the following furan synthesis. Identify them, and propose a mechanism for the transformation. 

The reaction occurs by two sequential nucleophilic acyl substitutions, the first by a cysteine residue in the enzyme, with phosphate as leaving group, and the second by hydride donation fromNADH, with the cysteine residue as leaving group. 

Two-electron reduction of the quinone provides the hydroquinone 10, which may also be formed by two sequential one-electron reductions. It has also been... 

Geometric considerations in cyclopolymerization are optimal for 1,6-dienes (see 4.4.1.1). Instances of cyclopolymerization involving formation of larger rings have also been reported (see 4.4.1.4), as have examples where sequential intramolecular additions lead to bicyclic structures within the chain (see 4.4.1.2). Various 1,4- and 1,5-dienes are proposed to undergo cyclopolymerization by a mechanism involving two sequential intramolecular additions (see 4.4.1.3). 

In addition to these cases, which are relatively simple because only two sequential reactions are involved, there are others involving many, many reactions. The methods given here apply as well, although in practical terms the rate constants can be refined for only one or two steps. The others must be fixed at their independently known values. 

Both the V3+-Cr2+ and the Tl3+-Fe2+ reactions consist of a pattern in which two sequential transition states are separated by one intermediate. A circuit corresponding... 

Figure 2. Thin-layer radiochromatogram of urine (100 il) from rats injected with labeled PbTx-3. TLC plates were developed in two sequential solvent systems chloroform ethyl acetate ethanol (50 25 25 80 10 10). Radioactive zones were scraped and counted in a liquid scintillation counter. Native PbTx-3 runs at 13 cm.

C13-0024. Nucleotides can contain more than one phosphate group. One example is energy-storing adenosine triphosphate (ATP), which is discussed in Chapter 14. An ATP molecule is formed in two sequential condensation reactions between phosphoric acid and the phosphate group of AMP ... 

Mechanism I illustrates an important requirement for reaction mechanisms. Because a mechanism is a summary of events at the molecular level, a mechanism must lead to the correct stoichiometry to be an accurate description of the chemical reaction. The sum of the steps of a mechanism must give the balanced stoichiometric equation for the overall chemical reaction. If it does not, the proposed mechanism must be discarded. In Mechanism I, the net result of two sequential elementary reactions is the observed reaction stoichiometry. 

Using the periodic DPT double-reference model, the reduction of adsorbed O2 (O2) was found to occur by two sequential steps ... 

A) and (10 A), while the low intensity ion beam (10 to 10 A) is measured simultaneously in the low-level detector. A second sequence shifts all masses to monitor U in the ion counting channel relative to U. A comparison of the two sequential measurements using different collector configurations provides an... 

The derivative-forming process in pyrolytic alkylation involves two sequential reactions deprotonation of the acidic substrate in aqueous solution by the strongly basic tetra-alkylammonium ion and the thermal decomposition of the quaternary M-alkylammonium salt formed to give a tertiary amine and alkyl derivative. For some weak acids both processes may occur virtually simultaneously in the injector oven of the gas chromatograph. 

In the presence of a very strong base, such as an alkyllithium, sodium or potassium hydride, sodium or potassium amide, or LDA, 1,3-dicarbonyl compounds can be converted to their dianions by two sequential deprotonations.79 For example, reaction of benzoylacetone with sodium amide leads first to the enolate generated by deprotonation at the more acidic methylene group between the two carbonyl groups. A second equivalent of base deprotonates the benzyl methylene group to give a dienediolate. 

Redox-sensitive resin 24 designed for solid-phase peptide synthesis (SPPS) [29] was prepared from commercially available 2,5-dimethylben-zoquinone in seven steps [30] and loaded to a support via a Wittig reaction. Release of the peptide occurs using two sequential mild conditions, reduction with NaBH4 followed by TBAF-catalyzed cyclic ether formation (Scheme 8) which provide orthogonality to acid sensitive reactions. 

Zheng A, Shan D, Shi X, Wang B. A model resin linker for solid-phase peptide synthesis which can be cleaved using two sequential mild reactions. J Org Chem 1999 64 7459-7466. 

Figure 4.6. Cumulative sums of extractable Ca, Mg, and Mn in arid soil J3, BIO, and SI in consecutive steps of two sequential dissolution procedures.

After intravenous administration, about 80-90% of the dose is catabolized in the liver by dihydropyrimidine dehydrogenase (DPD) [38] (Figure 14.3). The formation of the inactive 5-fluoro-5,6-dihydrouracil (5-FUH2) by DPD is the rate-limiting step of 5-FU catabolism [39]. DPD is widely distributed among tissues, with the highest levels found in the liver. Once 5-FU entered tumor cells, its antitumor effect is mainly dependent on the extent of 5-FU anabolism. After two sequential anabolic steps involving thymidine phosphorylase (TP) and thymidine kinase... 

Since the substituted hydroquinones and quinone dioximes are better electron donors than hexamethylbenzene (as established by cyclic voltammetric studies), donor-induced disproportionation (to generate NO+ NOf) is even more favored. Furthermore, either two successive one-electron oxidations of hydro-quinone (or quinone dioxime) by NO + followed by the loss of two protons from the dication or two sequential oxidation/deprotonation steps complete the oxidative transformation in equation (97). Importantly, the ready aerial oxidation of NO to NO provides the basis for the nitrogen oxide catalysis of hydroquinone (or quinone dioxime) autoxidation as summarized in Scheme 26. 

Two sequential lithiations and treatments with different bifunctional electrophiles make possible one-pot syntheses of relatively complex molecules. Thus, in the [1+2+2] annulation depicted in Scheme 69, alkylation of 1-benzylbenzotriazole 399 with 2-bromoacetaldehyde diethyl acetal to give intermediate 426 is followed by alkylation with W-benzylideneaniline to produce derivative 427. Following treatment with formic acid causes cyclization to ethoxypyrrolidine 428 that subsequently eliminates ethanol and benzotriazole to give pyrrole 429 <1997JHC1379>. 

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