Pseudobase

Protoporphyrin-IX, N-methyl-, 4, 396 Protoporphyrins, 4, 382 photooxygenation, 4, 402 Prototropic tautomerism polyheteroatom six-membered rings, 3, 1055 Prozapine properties, 7, 545 Pschorr reaction carbolines from, 4, 523 dibenzazepines from, 7, 533 dibenzothiophenes from, 4, 107 phenanthridines from, 2, 433 Pseudilin, pentabromo-synthesis, 1, 449 Pseudoazulene synthesis, 4, 526 Pseudobases in synthesis reviews, 1, 62 Pseudocyanines, 2, 331 Pseudothiohydantoin synthesis, 6, 296 Pseudouracil structure, 3, 68 Pseudoyangonin IR spectra, 3, 596 Pseudoyohimbine synthesis, 2, 271 Psicofuranine biological activity, 5, 603 as pharmaceutical, 1, 153, 160... 

III. Structure and Mechanism of Formation of Derivatives of the Heterocyclic Pseudobasic Carbinolamines... 

The heterocyclic pseudobasic carbinolamines show a very varied reactivity. However, the structure of a large number of their transformation products, in particular those from which conclusions have been drawn as to the structure of the initial pseudo base, are incorrect even in the most recent literature. 

This dimeric formulation also accounts for the thermal disproportionation of the compound into a mixture of 2-methyl-l,2,3,4-tetrahydro-jS-carbohne and 2-methyl-jS-carboline anhydro-base. Normal pseudobase formation (453 R = CHs ) takes place in the case of 9-methyl-3,4-dihydro-j3-carbohne methiodide (452 R = CHg). Neither the dimeric anhydro-base nor the -methyl pseudo-base undergo a base-catalyzed disproportionation reaction to give the 1,2,3,4-tetrahydro-and the l-oxo-l,2,3,4-tetrahydro-jS-carboline in a manner analogous... 

In those few cases where hydration and pseudobase formation parallel each other, the agreement can be traced to the fortuitous circumstance that the structure and electronic configuration of the molecule permit both phenomena to occur simultaneously. Quin-azoline-3-methochloride, one of these rare examples, is discussed in Section III,C, 1. 

Covalent hydration and pseudobase formation in transition metal polypyridyl complexes reality or myth N. Serpone, G. Ponterini, M. A. Jamieson, F. Bolletta and M. Maestri, Coord. Chem. Rev.,... 

Four anthocyanin species exist in equilibrium under acidic conditions at 25°C/ according to the scheme in Figure 4.3.3. The equilibrium constant values determine the major species and therefore the color of the solution. If the deprotonation equilibrium constant, K, is higher than the hydration constant, Kj, the equilibrium is displaced toward the colored quinonoidal base (A), and if Kj, > the equilibrium shifts toward the hemiacetalic or pseudobase form (B) that is in equilibrium with the chalcone species (C), both colorless." - Therefore, the structure of an anthocyanin is strongly dependent on the solution pH, and as a consequence so is its color stability, which is highly related to the deprotonation and hydration equilibrium reaction constant values (K and Kj,). 

The structure complexity also interferes with the equilibria in acidic medium, as shown in Figure 4.3.3. The deprotonation equilibrium constant value (KJ of zebrinin was higher than the hydration constant (Kj,), leading to the formation of a greater amount of colored quinonoidal with no formation of the colorless species, pseudobase or chalcone. ... 

An anthocyanin occurs in solution as a mixture of different secondary structures, a quinonoidal base, a carbinol pseudobase, and a chalcone pseudobase. ° hi addition, different mechanisms for the stabilization of anthocyanins lead to the formation of tertiary structures such as self-association, inter-, and intra-molecular co-pigmentation. ... 

The immonium system 11 has been examined by Czech authors (22,24,25), who claimed that it reacts with hydroxide ions in aqueous media to form pseudobases. This implies that hypecorine (8) and hypecorinine (9) may be artifacts of isolation. In all probability, the quaternary immonium system... 

Diphenylpyrido[l,2-3][l,2,4]triazinium fluoroborate 97 promptly reacted with nucleophiles (such as hydroxide, alkoxide, or cyanide ion) at the 2-position to give the stable pseudobases 100 (Equation 9) <2003ARK155>. 

Quantification of anthocyanins takes advantage of their characteristic behavior in acidic media anthocyanins exist in these media as an equilibrium between the colored oxo-nium ion and the colorless pseudobase form. Using an average extinction coefficient, the total content of anthocyanins may be estimated from the absorption of the total extracts at 520 nm (Moskowitz and Hrazdina 1981). 

Equilibrium studies. Acidities of thiazolium cations, such as 213, cannot be measured in basic aqueous solution because the hydroxyl adduct ( pseudobase ) 216 of the thiazolium cation is formed rapidly and is subject to base-catalyzed ring opening (Scheme 36).151 In DMSO, formation of the carbene dimer 217 from 213 and 214 is a complicating factor.8 If indicator anion (In") was added to a solution of 213, a very rapid drop in absorbance was followed by a somewhat... 

Transition state pKn values may also be estimated for reactions which involve nucleophilic attack by water and by hydroxide ion (Kurz, 1963, 1972). Such may be the case in the formation of pseudobases from quaternary heterocyclic cations (32a,b), a number of which have rates of... 

In some cases two isomeric tropones (4-oxo and 6-oxo) and two or more tropilidenes are formed from tropylium salts [66JCS(C)926] or from the equivalent pseudobases (cycloheptatrienols or tropols 69ZOB2601). Finally nucleophilic attack can generate an unstable tropol that yields, on oxidation, the desired tropone (78AJC1607). 

Tricyclic complex 290b is obtained from its pseudobase 289b (Scheme 72 83AG572) the corresponding tropone complex was synthesized from dibenzotropone and Cr(CO)6 [83AG(S)734]. 

Covalent Hydration of Nitrogen-Containing Heterocycles and Heterocyclic Pseudobases... 

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