ABSTRACT
High Resolution Diffusion-ordered Spectroscopy (HR-DOSY) is a valuable tool for mixture analysis by NMR. It separates the signals from different components according to their diffusion behavior, and can provide exquisite diffusion resolution when there is no signal overlap. In HR-DOSY experiments on (1)H (by far the most common nucleus used for DOSY) there is frequent signal overlap that confuses interpretation. In contrast, a (13)C spectrum usually has little overlap, and is in this respect a much better option for a DOSY experiment. The low signal-to-noise ratio is a critical limiting factor, but with recent technical advances such as cryogenic probes this problem is now less acute. The most widely-used pulse sequences for (13)C DOSY perform diffusion encoding with (1)H, using a stimulated echo in which half of the signal is lost. This signal loss can be avoided by encoding diffusion with (13)C in a spin echo experiment such as the DEPTSE pulse sequence described here.
Subject(s)
Magnetic Resonance Spectroscopy/methods , Alcohols/chemistry , Algorithms , Complex Mixtures/analysis , Data Interpretation, Statistical , Deuterium , Diffusion , WaterABSTRACT
Angiopterlactones A (1) and B (2), two unique lactones, and three known lactones, osmundalactone (3), osmundalin (4), and 3,5-dihydroxy-gamma-caprolactone (5), have been isolated from the rhizome of Angiopteris caudatiformis. The structures of 1 and 2 were determined by NMR and MS methods, and the structure of 2 was confirmed by X-ray crystallography. The absolute configurations of 1 and 2 were assigned by application of the CD excitation chirality method and the modified Mosher's method. Compound 1 was slightly cytotoxic against HeLa cells, with an IC(50) value of 68.8 microM, and compounds 3 and 4 showed moderate insect antifeeding activity against Plutella xylostella and Heliothis virescens.
