On the detection of both carbonyl and hydroxyl oxygens in amino acid derivatives: a O-17 NMR reinvestigation

 
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2004 (EN)
On the detection of both carbonyl and hydroxyl oxygens in amino acid derivatives: a O-17 NMR reinvestigation (EN)

Theodorou, V. (EN)

Πανεπιστήμιο Ιωαννίνων. Σχολή Θετικών Επιστημών. Τμήμα Χημείας (EL)
Theodorou, V. (EN)

The hypothesis and the conclusions of previous O-17 NMR studies on the detection of both oxygens of the carboxylic group of Boc-[O-17]Tyr(2,6-diClBzl)-OH in DMSO-d(6) solution (V. Tsikaris et al., Tetrahedron Lett. 2000, 41, 8651) are reconsidered. The appearance of two discrete resonances at 340 and 175 ppm of this protected amino acid is not now attributed: (a) to the reduction of the intramolecular conformational exchange rate, due to the effect of intramolecular hydrogen bonding of the hydroxy part of the carboxyl with the carbonyl oxygen of the Boc-group, and (b) to the effect of solvent viscosity, suggested in the mentioned study. The cause of this phenomenon is now attributed to a strong hydrogen bonding of the polar proton acceptor solvent DMSO with the carboxy group, which effectively reduces the proton exchange rate, thus becoming slow on the O-17 NMR time scale. (C) 2004 Elsevier Ltd. All rights reserved. (EN)

o-17 nmr (EN)

Πανεπιστήμιο Ιωαννίνων (EL)
University of Ioannina (EN)

Tetrahedron Lett (EN)

English

2004

<Go to ISI>://000189233200050

Elsevier (EN)



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