Structure Elucidation and Theoretical Investigation of Key Steps in the Biogenetic Pathway of Schisanartane Nortriterpenoids by Using DFT Methods

Abstract

Rubrifloradilactone C (4), a novel bioactive nortriterpenoid, along with four other nortriterpenoids (1-3, 5) were isolated from Schisandra rubriflora. The structure of 4 was determined by extensive NMR spectral analysis, computational evidence by using the GIAO method at the B3LYP/6-311++G(2d,p)//B3LYP/6-31G(d) levels, and X-ray analysis. DFT at the B3LYP/6-311+G(d,p) level was selected to clarify the key mechanistic steps in the formation of 1 and 4 through transition-state (TS) investigations. The effect of enzymes on the TS barriers was considered by using the polarized continuum model. Other possible products based on the new mechanism were predicted.

Triterpenoids from the Schisandraceae family: an update

“…In addition, the structure of kadpolysperin H (34) 8 and several stereogenic centers of schinortriterpenoids were mistaken by them. For example, schisandilactones B-D (239-241) 9 and lancifodilactone R (251), 10 analogues of rubrioradilactone C (220) whose structure was conrmed by X-ray diffraction, 11 should present with a 15a-OH, instead of a 15b-OH as they described. 7 Additionally, some confusing nomenclatures are found in the original articles.…”

Four New Nortriterpenoids from Schisandra lancifolia

“…Comparison of the 1D-NMR data of 3 with those of 1 showed that the difference was that the oxygenated quaternary C(25) of 1 was replaced by a CH group (Fig. 1) showed that 4 possessed the same planar structure as rubrifloradilactone C [11]. The significant chemical-shift differences observed in the NMR spectra between 4 and rubrifloradilactone C were associated with the signals at C(5)ÀC(8) and C(11).…”

Integrated X-Ray, NMR, ECD, and Computational Approaches to Assign the Stereochemistry of Nortriterpenoids

“…The absolute configuration of a number of nortriterpenods was unambiguously assigned by single-crystal X-ray diffraction using Cu or Mo Kα radiation. These include schilancitrilactone A, B, and C, 8 wuweizidilactone P, 9 arisanlactone A, 7 propindilactone H, 10 micrandilactone I, 6 micrandilactone H, 5 lancolides A, B, C, and D, 11 preschisanartanin O, 11 lancifonin A, 12 schicagenin A, 13 rubrifloradilactone C, 14 and wilsonianadilactone A 15 (Figure 1). However, a crystal that diffracts well to solve absolute configuration directly is always challenging.…”