Computer supported structure elucidation of polymethoxy‐ and polyacetoxyxanthones. V—¹³C NMR spectroscopy of substituted xanthones

Abstract

A procedure for developing =C NMR chemical shift additivity rules for all 136 polymethoxyxanthones and all 136 polyacetoxyxanthones, based on multiple linear regression analysis, is reported. The influence of steric interactions between the substhents on the chemical shifts of the carbon atoms in the xanthone ring system is discussed and induded in the calculations of the additivily rules for the polymethoxyxanthones. The derived chemical shift increments are implemented into the computer program SEOX 1. The extended program, SEOX 2, allows an automated structure elucidation of polyhydroxy-, polymethoxy-and polyacetoxyxanthones. The increments are tested lasing the leave-one-out method in conjunction with SEOX 2, and have been found to be very suitable for this purpose.

Xanthones from the Roots ofPolygala caudataand their Antioxidation and Vasodilatation Activitiesin vitro

“…Three new xanthones, 2-hydroxy-1,6,7-trimethoxyxanthone (1), 1,4-dimethoxy-2,3-methylenedioxyxanthone (2), and 7-hydroxy-1,2-dimethoxyxanthone (3), together with five known compounds, 2,7-dihydroxy-1-methoxyxanthone (4), 1-methoxy-2,3methylenedioxyxanthone (5), 7-hydroxy-1-methoxyxanthone (6), euxanthone (1,7-dihydroxyxanthone) (7), and gentitein (1,3,7-trihydroxyxanthone) (8), were isolated from the roots of Polygala caudata. Their structures were established on the basis of spectral evidence.…”

“…The 1 H-NMR spectrum showed a hydroxy (d = 6.01, 1H, s) and three methoxy groups (d = 4.05, 4.01 and 3.99, each 3H, s), along with four aromatic proton signals. In the 13 C-NMR spectrum, the signal at d = 62.7 was indicative of di-ortho-substituted methoxy groups [8]. In the NOE-SY spectrum (in CDCl 3 ), the signal at d = 6.01 (OH-2) showed an NOE correlation with d = 4.06 (OMe-1), while the signal at d = 6.86 (H-5) correlated with d = 4.01 (OMe-6), and the signal at d = 7.65 (H-8) with d = 3.99 (OMe-7).…”

Assignment of 1 H and 13 C NMR Chemical Shifts of Nitroxanthones and Development of Additivity Rules

“…The development of a I3C NMR shift increment system with dummy parameters on the basis of MLR analysis depends on the assumption that substituent effects behave in an additive manner. Such relation is 6,-x = BIK + IklP, + Ik, P, + Ik, P3 + Ik, P4( +STP) (1) The dependent variable 6,, is the measured 13C NMR shift of a definite C atom signal of a nitroxanthone.…”

“…'H NMR data for xanthone (1) and fourteen nitroxanthones(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15) …”

Interactive computer system for the simulation of carbon-13 nuclear magnetic resonance spectra

“…A logical extension is the development of computer programs to apply existing models. These have proven useful, but they are limited to specific models previously determined (17)(18)(19).…”