A slow rate exchange process allows the detection of both carbonyl (C=O) and hydroxyl (-OH) O-17 nuclear magnetic resonances of the carboxylic group

 
This item is provided by the institution :
University of Ioannina
Repository :
Repository of UOI Olympias
see the original item page
in the repository's web site and access all digital files if the item*
share



2000 (EN)
A slow rate exchange process allows the detection of both carbonyl (C=O) and hydroxyl (-OH) O-17 nuclear magnetic resonances of the carboxylic group (EN)

Tsikaris, V. (EN)

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

In this study we report, for the first time, on the detection of both the carbonyl (-C=O) and the hydroxyl (-OH) O-17 resonances of the carboxylic group by O-17 NMR spectroscopy. Two well separated peaks, at 340.3 and 175 ppm, were detected for the -C=O and -OH groups, respectively, of Boc[O-17]Tyr(2,6-diClBzl)-OH in DMSO-d(6). This finding is attributed to the participation of the carboxylic group in a rather strong hydrogen-bonded interaction. These resonances disappeared in the presence of a small quantity of TFA (trifluoroacetic acid), which, however, did not cleave the Boc-group and a broad resonance was detected for both oxygens. In fact, this result indicates that the proposed hydrogen-bonded interaction is not stabilized in the presence of TFA, which is a very strong hydrogen bond breaker. Only one broad signal was observed for both carboxylic oxygens at 251.8 ppm for the HCl[O-17]Tyr(2,6-diClBzl)-OH in DMSO-d(6) solution, suggesting that the carbonyl oxygen of the Boc-group is probably the proton acceptor group of the carboxylic hydrogen, stabilizing a gamma -turn like structure. A single relatively sharp resonance appearing in chloroform, (247.5 ppm) upheld shifted by similar to 14.5 ppm, compared to the resonance found in DMSO-d(6) for Boc-[17(O)]Tyr(2,6-ClBzl)-OH in the presence of TFA, is attributed to a gamma -turn fraction being in a fast exchange with the open form. (C) 2000 Elsevier Science Ltd. All rights reserved. (EN)

Πανεπιστήμιο Ιωαννίνων (EL)
University of Ioannina (EN)

Tetrahedron Lett (EN)

English

2000

<Go to ISI>://000165150200050

Elsevier (EN)



*Institutions are responsible for keeping their URLs functional (digital file, item page in repository site)