Absolute configuration of the ocimene monoterpenoids from Artemisia absinthium

2019

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The bark of the roots of Piscidia carthagenensis afforded the known insecticides rotenone (1) and millettone (2), as well as the new rotenoid piscicartone (3). The structure of 3 followed from nuclear magnetic resonance studies, while its absolute configuration (AC) was determined by vibrational circular dichroism (VCD) measurements in comparison with discrete Fourier transform B3LYP/DGDZVPcalculated spectra using the Compare VOA software. In addition, the AC of 1 and 2 was verified using the same VCD methodology.

supporting

confidence: 57%

Piscicartone, a Rotenoid From Piscidia carthagenensis

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Pérez‐Hernández

2019

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“…The VCD spectra compared well with the calculated spectra of the 2 enantiomers. 31 VCD studies of 2 isolates 32 from Bubonium graveolens provided their AC as (−)-(1S,5R,6S)-2,7,7-trimethylbicyclo[3.1.1] hept-2-en-6-yl acetate (19) and its acetyl derivative 20 (Figure 4). The compounds were already known in the species, although this is the first report on the AC of (−)-20.…”

Section: Monoterpenoids the Formulas Of The 28 Monoterpenoids Includmentioning

confidence: 99%

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

Río

2021

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Although demonstrated in 1975, vibrational circular dichroism (VCD) finally started to popularize during this century as a reliable tool to determine the absolute configuration (AC) of organic molecules. This research field continues to be a very dynamic one, in particular for the study of natural products which are a unlimited source of chiral molecules. It therefore turns of interest to summarize the accomplishments published in recent years and to comment on some eventual difficulties that emerged in rare cases to complete the AC determination task. Therefore the aim of this review is to update VCD results for the AC assignment of natural products published from 2015 to 2019, a period in which VCD was reported in some 126 publications involving almost 300 molecules. They are organized according the type of studied metabolite allowing an easily search. The molecules correspond to 28 monoterpenes concerning 17 papers, to 42 sesquiterpenes in 14 papers, to 51 diterpenes in 19 publications, to 5 other terpenoids in three papers, to 48 aromatic molecules in 15 reports, to 20 polyketides in 10 publications, to 27 miscellaneous formulas also in 10 papers, and to 76 nitrogen containing compounds, which include alkaloids and their synthetic analogs, in 38 articles. The landscape of reviewed molecules is quite wide as it goes from simple monoterpenes, like borneol or camphor, to very relevant biological molecules like the alkaloid cocaine or tadalafil samples to distinguish genuine and counterfeit Cialis®. In addition, 5 natural products and a simple derivative published outside the reviewed period, were used to illustrate some aspects of density functional theory calculations.

“…A general lack of VCD studies of acyclic monoterpenes like linalol, citronellol, and citronellal is observed, although the ocimenes from the essential oils of Artemisia absintium could be studied [24] since a significant molecular portion is rigid due to the presence of a conjugated diene. Of relevance is also to note that an AC study of conformational very flexible citronellal by molecular rotational resonance, using microwaves in the 2-8 GHz region, was reported recently [25], also evidencing a very high number of relevant conformers.…”

mentioning

confidence: 99%

Difficulties to Determine the Absolute Configuration of Guaiaretic Acid

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Burgueño‐Tapia

2018

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An account of the difficulties to determine the absolute configuration (AC) of guaiaretic acid (1a), using contemporary methodology, is described in commemoration of the century of its structure elucidation. In fact, the herein studied molecule was the derived diacetate 1b, since the natural lignan slowly decomposes upon manipulation. Single crystal X-ray diffraction of 1b demonstrated the structure, but calculation of Flack and Hooft parameters to know the AC was unsuccessful since the crystals were triclinic, P-1, which is a centro-symmetric space group. In turn, manual band to band comparison of experimental and DFT B3LYP/DGDZVP calculated VCD spectra of 1b allowed ascertaining its AC, although automatic comparison using the CompareVOA software was not very successful. This behavior is associated to the fact that the studied molecule has a sole stereogenic center located on the acyclic portion of a carbon chain possessing two quite similar substituents. The behavior is discussed in relation to cases where the molecular flexibility also generates a very large number of conformers.