¹³C NMR Spectra of Several Tricyclo[6.3.0.0^2,6]undecane Derivatives

Abstract

MaterialsBilirubin (BR) (analytical-reagent grade) was obtained from Fluka. The dimethyl ester (BRME) was prepared by a well established procedure8 and purified by repeated thin-layer chromatography [SO, preparative plates, 2mm layer, Merck; mobile phase, CHCI,-CH,OH (20: l)].The NMR solvents (99.5% isotopic purity) were distilled in vacuo (DMSO-d6) or under a dry argon atmosphere (CD,OD) before use. For NOE and long-range correlation experiments the solutions (c = 0.05 M for BR, 0.1 M for BRME) were degassed by bubbling with dry argon. MethodsAll Nh4R spectra were recorded on a Bruker WM-360 spectrometer operating at a 90.56MHz 13C frequency in the PFT mode at 305K with quadrature detection. Acquisition and data processing were under the control of the built-in Aspect 2000 minicomputer. TMS served as internal reference for both nuclei.A 10mm broad band probe head was used for the 13C spectra of BR. Selective 5mm probe heads were used for the 13C spectra of BRME and all lH spectra.'H-lHNOE difference experiments for BRME in DMSO-d,-CD,OD (63 : 37 w/w; composition determined by quantitative 13C NA4R after degassing). The methyl signals were selectively irradiated in separate experiments for 0.4s with low r.f. power (45 dB attenuation of the low-power decoupling stage) immediately before a nonselective 45' observing pulse. Alternating every 16 scans, spectra with off-resonance irradiation were subtracted directly in the computer memory. Assignments of BRME in OD (63 : 37) t,' was incremented from 1/2SW1 to DPl/2SW, while t; was decremented synchronously from the latter value to the former, both in steps of 1/2SW1. DP,, the number of data points in the t , dimension, was set to SW,/J, (SW, is the spectral width in the proton dimension and J, the coupling constant for which polarization transfer is the optimum). This makes the time between the excitation and polarization transfer pulses equal to l/U, and the whole period can be used to increment tl without an increase in overall time. A was set to 1/65, to compromise between relaxation and polarization. The ? r , pulses were composite pulses ( T /~~-T~-T /~~)~ for homogeneous inversion. Typical parameters for 2D heteronuclear correlation via long-range couplings (COLOC) were as follows: spectral widths (Hz), 12O(lH), 5500(13C); acquisition size