Publications by authors named "Hector M Arreaga-Gonzalez"
The occurrence of racemic and enantiomerically enriched (scalemic) mixtures of secondary metabolites in their natural sources is a rare phenomenon. The unprecedent case of enantiomeric variations from levorotatory to dextrorotatory, and back to levorotatory, passing through an almost racemic mixture, was recently documented for areolal, the major epoxythymol of Piptothrix areolare. In an attempt to shed some light to understand the reasons for such an unusual behavior, herein, we evaluated this phenomenon by correlating the areolal enantiomeric purity with several environmental variables, including temperature, humidity, rain precipitation, wind speed, and radiation during over 1 year of the plant life cycle.
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- - Knowledge of the chiral composition and absolute configuration (AC) of epoxythymols is crucial, as they can exist as scalemic mixtures or pure enantiomers, and methods like NMR and VCD have been used for their characterization.
- - The study explores the use of electronic circular dichroism (ECD) for determining the AC of an epoxythymol, linking its results with the properties of related known compounds to avoid extensive computations.
- - Various epoxythymol compounds were isolated from plant extracts, and their structures were confirmed through advanced techniques, with the enantiomeric compositions specifically measured using H NMR-BINOL, and AC determined using ECD and VCD methods.
Article Synopsis
- A natural compound, areolal, shows significant variations in its absolute configuration within the same species, with samples displaying different enantiomeric compositions over time from the same geographical area.
- These variations were measured using NMR data with BINOL as a chiral solvating agent, uncovering a unique phenomenon in the compound’s behavior.
- The findings highlight potential influences of environmental factors and biochemical processes, emphasizing the importance of careful evaluation of enantiomeric composition for natural products intended for human use.
A biomimetic transformation of p-menthene glucosides into aromatic monoterpenoids that alluded to mechanisms for essential oil metabolism, which lines up with the precepts of molecular economy, is described. Acid treatment of (-)-(3 S,4 S,6 R)-3,6-dihydroxy-1-menthene 3- O-β-d-glucopyranoside (1) and (-)-(3 S,4 R,5 R,6 S)-3,5,6-trihydroxy-1-menthene 3- O-β-d-glucopyranoside (2), from Ageratina glabrata, yielded p-cymene (7) and carvacrol (9). The stable oxidized intermediates (+)-(3 S,4 S,6 R)-3,6-dihydroxy-1-menthene (3), (+)-(1 S,4 S,6 R)-1,6-dihydroxy-2-menthene (4), (+)-(1 R,4 S,6 R)-1,6-dihydroxy-2-menthene (5), (+)-(4 S,6 R)-yabunikkeol (6), (+)-(4 S)-carvotanacetone (8), (+)-(1 S,4 S,5 R,6 R)-1,5,6-trihydroxy-2-menthene (15), (+)-(1 R,4 S,5 R,6 R)-1,5,6-trihydroxy-2-menthene (16), and the new (+)-(4 S,5 R,6 S)-1(7),2-menthadiene (17) permitted establishment of the reaction mechanisms.
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- - The study introduces a method to analyze the enantiomeric excess and absolute configuration of natural epoxythymols using BINOL as a chiral agent alongside vibrational circular dichroism (VCD).
- - Five epoxythymol compounds from Ageratina glabrata were isolated, three of which were enantiomerically pure, while others exhibited scalemic mixtures, highlighting variations in stereochemistry.
- - The research also examined the racemization of epoxythymol derivatives and their specific rotations, indicating a range of mixtures and providing new insights since prior analyses of these compounds' absolute configurations had been limited.
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.
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