Computationally Assisted Structural Revision of Flavoalkaloids with a Seven-Membered Ring: Aquiledine, Isoaquiledine, and Cheliensisine

Abstract

Aquiledine and cheliensisine are flavoalkaloids isolated from Aquilegia ecalcarata and Goniothalamus cheliensis, respectively. Different structures have been proposed for these flavoalkaloids; however, their 1H and 13C NMR spectroscopic data were virtually identical. In this study, the structures of aquiledine and cheliensisine were revised on the basis of the DFT calculation of NMR data including DP4+ and J-DP4 analysis, as well as specific rotations. Similarly, the structure of isoaquiledine, a regioisomer of aquiledine, was also revised. A biosynthetic pathway of these flavoalkaloids is proposed.

Metabolites With Cytotoxic Activities From the Mangrove Endophytic Fungus Fusarium sp. 2ST2

“…Subsequently, the 13 C NMR calculations of (1 R *, 3 S *, 4 R *, 5 S *, 6 S *, 7 S *, 10 S *, 21 R *, 15 R *, 16 S *) -1a and (1 R *, 3 R *, 4 S *, 5 S *, 6 S *, 7 S *, 10 S *, 21 R *, 15 R *, 16 S *) -1b were carried out using the GIAO method at mPW1PW91-SCRF/6–311+G (d, p)/PCM (MeOH). The results of the DP4+ probability analysis ( Smith and Goodman, 2010 ; Kawazoe et al, 2020 ; Xu et al, 2021 ) showed that 1a was the most likely candidate structure, with a better correlation coefficient ( R 2 = 0.99891) and a high DP4+ probability of 100% (all data) probability ( Figure 4 ). Similarly, 13 C NMR calculations with the DP4+ probability analysis of the two isomers [(1 R *, 3 S *, 4 S *, 5 S *, 6 S *, 7 S *, 10 S *, 21 R *, 15 R *, 16S*) -2a and (1 R *, 3 R *, 4 R *, 5 S *, 6 S *, 7 S *, 10 S *, 21 R *, 15 R *, 16 S *)- 2b ] of 2 were performed.…”

“…The cross-peaks of H-12/H-10/ H 3 -22/H-7/H 3 -20 suggested that these protons were co-facial, while the correlations of H 3 -21/H-15/H-6 showed that these protons were on the other face. Considering the absence of The results of the DP4+ probability analysis (Smith and Goodman, 2010;Kawazoe et al, 2020;Xu et al, 2021) showed that 1a was the most likely candidate structure, with a better correlation coefficient (R 2 = 0.99891) and a high DP4+ probability of 100% (all data) probability (Figure 4). Similarly, Aiming at determining the absolute configuration of 1, the ECD calculation was performed at the WB97XD/CC-PVDZ level.…”

Penitol A and Penicitols E–I: Citrinin Derivatives from Penicillium citrinum and the Structure Revision of Previously Proposed Analogues

“…The anti -configuration at C-3 and C-4 in penitol A ( 1 ) was deduced by the 1 H– 1 H coupling constant of H-3 and H-4 (about 6.4 Hz), , the nuclear Overhauser effect spectroscopy (NOESY) correlation of H-4 and H 3 -11 (Figure S1 and Table S1), and the DP4+ analysis based on the NMR calculation (Tables S8–S10). The absolute configuration of compound 1 was established by ECD calculations.…”

“…During the determination of the relative and absolute configurations of compounds 1 – 6 , 1 H– 1 H coupling constants, DP4+ analyses based on density functional theory gauge-independent atomic orbital (DFT-GIAO) NMR calculations, time-dependent density functional theory electronic circular dichroism (TDDFT-ECD) calculations, and the X-ray diffraction analysis were combined. In addition, the structures of penicitol A and two synthesis intermediates, compounds 11 and 14- epi - 11 , were revised.…”

Sesquiterpene and Sorbicillinoid Glycosides from the Endophytic Fungus Trichoderma longibrachiatum EN-586 Derived from the Marine Red Alga Laurencia obtusa

“…GIAO (gauge-independent atomic orbital) NMR chemical calculations were conducted using an equation described previously. Finally, the NMR chemical shifts and shielding tensors ( 1 H and 13 C) were analyzed and compared with the experimental chemical shifts using DP4+ probability ( Figure S25 ) [ 30 , 31 ].…”