Tetramethyl-Ortho-quinodimethane, First Member of a Family of Custom-Tailored Cheletropic Spin Traps for Nitric Oxide
✍ Scribed by Dr. Hans-Gert Korth; Prof. Dr. Keith U. Ingold; Prof. Dr. Reiner Sustmann; Priv.-Doz. Dr. Herbert de Groot; Prof. Dr. Helmut Sies
- Publisher
- John Wiley and Sons
- Year
- 1992
- Tongue
- English
- Weight
- 397 KB
- Volume
- 31
- Category
- Article
- ISSN
- 0044-8249
No coin nor oath required. For personal study only.
✦ Synopsis
sugar, high sensitivity can still be achieved with UV detection (down approximately to the 1 pmole level, S/N M 2), although it is an order of magnitude less sensitive than fluorescence detection.
Although alditol benzoates have been reported to show poor separation with reverse phase HPLC,[31 the alditol naphthoates could be well separated by normal phase HPLC. Diastereomers differing by one stereocenter, for example, sorbitol/mannitol/duIcitol, xylitol/arabitol, fucitol/ quinovitol, and glucosaminitol/galactosaminitol are all well resolved. The amino alditols galactosaminitol and glucosaminitol are retained more strongly by the column than the oxygen sugars and are eluted last. In addition to their higher sensitivity of detection, the good HPLC separation of these 2-naphthoate derivatives offers an important advantage over the use of the benzoate chromophore.
When two or more 2-naphthoate chromophores are present in chiral compounds, exciton coupling interactions are often observed by circular dichroic spectroscopy (CD)."'' The resulting CD curve not only reflects the stereochemistry of the molecule but can be used as an additional handle for structural identification. With the use of a CD beam condenser and a microcell (100 pL, I cm), compounds bearing 2-naphthoate chromophores have yielded distinct CD spectra with 50 pmole of sample; ten times more sample is required with a regular CD cell (1 mL, 1 cm).
In conclusion, the advantages of the 2-naphthoate chromophore are evident in the ease of derivatization, the high sensitivity of detection, the good chromatographic behavior, and the possibility of further CD characterization.
Experimental Procedure
Preparation of 1: Imidazole (0.71 g) was suspended in benzene (40 mL) and cooled to 8 "C. A solution of 2-naphthoyl chloride (1.0 g) in benzene (10 mL) was added dropwise over IOmin, and the mixture stirred for 1 h at room temperature. The reaction mixture was filtered through Celite and lyophilized to afford the product (1.2 g. quantitative). Mannose. fucose. arabinose, galactose, glucose, quinovose, xylose, glucosamine hydrochloride, and galactosamine hydrochloride (5 pmol each) were stirred for 2 h at room temperature with NaBH, (10 mg) in water (1 mL). The reaction was quenched with aqueous HCI, and the resulting mixture evaporated six times with methanol. An aliquot (10 nmol of each sugar) was stirred in acetonitrile (0.2mL) with 1 (IOpmol) and DBU (10pmol) for 2 h at room temperature. After quenching with water, an aliquot (2 nmol) was evaporated in a silanized test tube. The residue was dissolved in dichloromethane, and aliquots were injected for HPLC analysis [Ill (Perkin-Elmer Series 4 Liquid Chromatograph and 7500 Data Station, Shimadzu RF-551 Fluorescence HPLC Monitor).