Functional Diversity in Ferns Is Driven by Species Richness Rather Than by Environmental Constraints.

Functional traits determine how species interact with their abiotic and biotic environment. In turn, functional diversity describes how assemblages of species as a whole are adapted to their environment, which also determines how they might react to changing conditions. To fully understand functional diversity, it is fundamental to (a) disentangle the influences of environmental filtering and species richness from each other, (b) assess if the trait space saturates at high levels of species richness, and (c) understand how changes in species numbers affect the relative importance of the trait niche expansion and packing. In the present study, we determined functional diversity of fern assemblages by describing morphological traits related to resource acquisition along four tropical elevational transects with different environmental conditions and species richness. We used several functional diversity indices and their standardized effect size to consider different aspects of functional diversity. We contrasted these aspects of functional diversity with climate data and species richness using linear models and linear mixed models. Our results show that functional morphological trait diversity was primarily driven by species richness and only marginally by environmental conditions. Moreover, increasing species richness contributed progressively to packing of the morphological niche space, while at the same time decreasing morphological expansion until a saturation point was reached. Overall, our findings suggest that the density of co-occurring species is the fundamental driving force of morphological niche structure, and environmental conditions have only an indirect influence on fern resource acquisition strategies.

Absolute configuration and conformational analysis of brevipolides, bioactive 5,6-dihydro-α-pyrones from Hyptis brevipes.

The (6'S)-configuration of brevipolides A-J (1-10), isolated from Hyptis brevipes, was established by X-ray diffraction analysis of 9 in conjunction with Mosher's ester analysis of the tetrahydro derivative 11 obtained from both geometric isomers 8 and 9 as well as by chemical correlations. The structure of the new brevipolide J (10) was characterized through NMR and MS data as having the same 6-heptyl-5,6-dihydro-2H-pyran-2-one framework possessing the cyclopropane moiety of all brevipolides but substituted by an isoferuloyl group instead of the p-methoxycinnamoyl moiety found in 8 and 9. Conformational analysis of these cytotoxic 6-heptyl-5,6-dihydro-α-pyrones was carried out on compound 9 by application of a protocol based on comparison between experimental and DFT-calculated vicinal (1)H-(1)H NMR coupling constants. Molecular modeling was used to correlate minimum energy conformers and observed electronic circular dichroism transitions for the isomeric series of brevipolides. Compounds 7-10 exhibited moderate activity (ED(50) 0.3-8.0 µg/mL) against a variety of tumor cell lines.

Vicinal 1H-1H NMR coupling constants from density functional theory as reliable tools for stereochemical analysis of highly flexible multichiral center molecules.

A protocol for stereochemical analysis, based on the systematic comparison between theoretical and experimental vicinal (1)H-(1)H NMR coupling constants, was developed and applied to a series of flexible compounds (1-8) derived from the 6-heptenyl-5,6-dihydro-2H-pyran-2-one framework. The method included a broad conformational search, followed by geometry optimization at the DFT B3LYP/DGDZVP level, calculation of the vibrational frequencies, thermochemical parameters, magnetic shielding tensors, and the total NMR spin-spin coupling constants. Three scaling factors, depending on the carbon atom hybridizations, were found for the (1)H-C-C-(1)H vicinal coupling constants: f((sp3)-(sp3)) = 0.910, f((sp3)-(sp2)) = 0.929, and f((sp2)-(sp2))= 0.977. A remarkable correlation between the theoretical (J(pre)) and experimental (1)H-(1)H NMR (J(exp)) coupling constants for spicigerolide (1), a cytotoxic natural product, and some of its synthetic stereoisomers (2-4) demonstrated the predictive value of this approach for the stereochemical assignment of highly flexible compounds containing multiple chiral centers. The stereochemistry of two natural 6-heptenyl-5,6-dihydro-2H-pyran-2-ones (14 and 15) containing diverse functional groups in the heptenyl side chain was also analyzed by application of this combined theoretical and experimental approach, confirming its reliability. Additionally, a geometrical analysis for the conformations of 1-8 revealed that weak hydrogen bonds substantially guide the conformational behavior of the tetraacyloxy-6-heptenyl-2H-pyran-2-ones.