Absolute Configuration of Menthene Derivatives by Vibrational Circular Dichroism

Abstract

The aerial parts of Ageratina glabrata afforded (-)-(3S,4R,5R,6S)-3,5,6-trihydroxy-1-menthene 3-O-β-d-glucopyranoside (1) and (-)-(3S,4S,6R)-3,6-dihydroxy-1-menthene 3-O-β-d-glucopyranoside (3). Acid hydrolysis of 1 yielded (+)-(1R,4S,5R,6R)-1,5,6-trihydroxy-2-menthene (5) and (+)-(1S,4S,5R,6R)-1,5,6-trihydroxy-2-menthene (6), while hydrolysis of 3 yielded (+)-(3S,4S,6R)-3,6-dihydroxy-1-menthene (10), (+)-(1R,4S,6R)-1,6-dihydroxy-2-menthene (11), and (+)-(1S,4S,6R)-1,6-dihydroxy-2-menthene (12). The structures of the new compounds 1, 2, 5-9, and 11 were defined by 1D and 2D NMR experiments, while the absolute configurations of the series of compounds were determined by comparison of the experimental vibrational circular dichroism (VCD) spectra of the 1,6-acetonide 5-acetate derived from 6 and of the 1,6-acetonide derived from 12 with their DFT-calculated spectra. In addition, Flack and Hooft X-ray parameters of 10 permitted the same conclusion. The results further led to the absolute configuration reassignment of 10 isolated from Brickellia rosmarinifolia, Mikania saltensis, Ligularia muliensis, L. sagitta, and Lindera strychnifolia, as well as of 11 from Cacalia tangutica, as ent-11.

Stereochemical assignment of fusiccocadiene from NMR shielding constants and vibrational circular dichroism spectroscopy

“…In recent years, vibrational circular dichroism (VCD) spectroscopy, the chiroptical version of infrared (IR) spectroscopy, has appeared as an increasingly powerful tool in the stereochemical assignment of natural products. [14][15][16][17][18] In this study, we confirm the correct chemical structure and absolute configuration of FCdiene by a combined experimental and theoretical NMR-and VCD-spectroscopic approach. To this end, 13 C-NMR shielding constants were calculated and the corresponding chemical shifts compared to experimental data.…”

“…This hampers the synthetic accessibility of compounds as well as the ongoing understanding of biosynthetic pathways. In recent years, vibrational circular dichroism (VCD) spectroscopy, the chiroptical version of infrared (IR) spectroscopy, has appeared as an increasingly powerful tool in the stereochemical assignment of natural products …”

Vibrational Circular Dichroism Absolute Configuration of Natural Products From 2015 to 2019

“…20 The structures of new natural menthenes 6, 8-11 (Figure 2), isolated from Ageratina glabrata, were defined by NMR experiments and the AC of the series followed from VCD studies of the 1,6-acetonide 5-acetate derived from 9 and the 1,6-acetonide derived from 12, as well as by the Flack and Hooft X-ray parameters of 10. 21 Likewise, this study permitted the reassignment of the AC of 10 isolated from several species [22][23][24][25][26] and of 11 from Cacalia tangutica 27 as ent-11.…”

Conformational, configurational, and supramolecular studies of podocephalol acetate from Lasianthaea aurea

“…22,[25][26][27][28][29] Consequently, a deeper understanding of the preferred conformation of 2 was gained through DFT computational calculations, a methodology successfully employed in conformational and configurational studies of natural terpenes 30 and terpene derivatives. 31 Thus, a model of 2 was built using the Spartan'04 software, and a conformational distribution analysis by the Monte Carlo protocol was undertaken. Calculations for the (7R)-2 enantiomer provided 24 conformers in a 10 kcal/mol energy gap.…”