A multifaceted study on the interaction of the cationic surfactant CTAB with calf thymus DNA was carried out by using different techniques. The measurements were done at different molar ratios X = [CTAB]/[DNA]. Results show the conformational change that DNA suffers due to the interaction with surfactant molecules at low molar ratios: the condensation of the polynucleotide, from an extended coil state to a globular state. The effect observed at the higher molar ratios is worth noting: the decondensation of DNA, that is, the transition from a compact state to a more extended conformation. Experimental data obtained confirm that this latter state is not exactly the same as that found in the absence of the surfactant. Attractive interactions between different parts of the molecule by ion correlation effects are the driving force to produce both the compaction and decompaction events. Results also show the importance of choosing both a proper system for the study and the most seeming measuring technique to use. The study demonstrates that, in some cases, the use of several techniques is desirable in obtaining reliable and accurate results.
Starting from a common lactam, (3R,8aS)-5-oxo-3-phenyl-2,3,6,7,8,8a-hexahydro-5H-oxazolo[3,2-a]pyridine (1), or its enantiomer, the enantioselective synthesis of 2-alkylpiperidines and cis- and trans-2,6-dialkylpiperidines is reported. The potential of this approach is illustrated by the synthesis of the piperidine alkaloids (R)-coniine, (2R,6S)-dihydropinidine, (2R,6R)-lupetidine, and (2R,6R)-solenopsin A, the indolizidine alkaloids (5R,8aR)-indolizidine 167B and (3R,5S,8aS)-monomorine I, and the nonnatural base (4R,9aS)-4-methylquinolizidine.
The absorption and fluorescence spectra of a set of dehydro and fully aromatic P-carboline (9Hpyrido[3,4-b] indole) derivatives have been investigated in aqueous solutions of varying acidity. Within the pH -range, cationic (nitrogen protonation) and neutral species are evidenced from both absorption and fluorescence spectra. Additional zwitterionic species can also be detected from the fluorescence spectra. In highly basic media, outside the pH -range, anionic species (pyrrolic nitrogen deprotonation) are formed. Ground state ionization constants for the different acid-base equilibria involving these species have been determined spectrophotometrically at 25 "C. Lowest excited singlet state pK,s have been estimated from the Forster-Weller cycle. The influence of structural variations on the spectra and on the acid-base properties of these compounds is discussed.As a continuation of the preceding paper,' we report now the results of our investigations on the acid-base properties and spectral characteristics of dehydro-(DB, 1) and fully aromatic (BC, 2) p-carbolines (9H-pyrido[3,4-b]indoles). Because of their extended x-electron systems, the acid-base and spectral properties of these compounds differ markedly from those of the less aromatic tetrahydro-P-carbolines (THBC 3), pre-' Taken from preceding paper. Taken from ref. 33.
Reaction of (R)-phenylglycinol with methyl 5-oxopentanoate gave either bicyclic lactam cis-1 (the kinetic product) or its isomer trans-1 (under equilibrating conditions) as the major products, which were converted to the corresponding (cis or trans) unsaturated lactams 4 and 5. On treatment with lithium alkyl (or aryl) cyanocuprates, these chiral building blocks undergo conjugate addition to give enantiopure trans-3,4-substituted 2-piperidone derivatives in high yield and stereoselectivity. The synthetic potential of this transformation is illustrated by the synthesis of (+)-femoxetine and the two enantiomers of the known antidepressant paroxetine.
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