1 H/ 13 C chemical shift calculations for biaryls: DFT approaches to geometry optimization

Twelve common density functional methods and seven basis sets for geometry optimization were evaluated on the accuracy of 1 H/ 13 C NMR chemical shift calculations for biaryls. For these functionals, 1 H shifts calculations for gas phase optimized geometries were significantly less accurate than those for in-solution optimized structures, while 13 C results were not strongly influenced by geometry optimization methods and solvent effects. B3LYP, B3PW91, mPW1PW91 and ω B97XD were the best-performing functionals with lowest errors; among seven basis sets, DGDZVP2 and 6-31G(d,p) outperformed the others. The combination of these functionals and basis sets resulted in high accuracy with CMAE min = 0.0327 ppm (0.76%) and 0.888 ppm (0.58%) for 1 H and 13 C, respectively. The selected functionals and basis set were validated when consistently producing optimized structures with high accuracy results for 1 H and 13 C chemical shift calculations of two other biaryls. This study highly recommends the IEFPCM/B3LYP, B3PW91, mPW1PW91 or ω B97XD/DGDZVP2 or 6-31G(d,p) level of theory for the geometry optimization step, especially the solvent incorporation, which would lead to high accuracy 1 H/ 13 C calculation. This work would assist in the fully structural assignments of biaryls and provide insights into in-solution biaryl conformations.

Cyclohumulanoid Sesquiterpenes from the Culture Broth of the Basidiomycetous Fungus Daedaleopsis tricolor

A series of cyclohumulanoids, i.e., tricocerapicanols A–C (1a–1c), tricoprotoilludenes A (2a) and B (3), tricosterpurol (4), and tricoilludins A–C (5–7) were isolated along with known violascensol (2b) and omphadiol (8) from the culture broth of Daedaleopsis tricolor, an inedible but not toxic mushroom. The structures were fully elucidated on the basis of NMR spectroscopic analysis, and the suggested relative structures were confirmed via density functional theory (DFT)-based chemical shift calculations involving a DP4 probability analysis. In the present study, the 1H chemical shifts were more informative than the 13C chemical shifts to distinguish the diastereomers at C-11. The absolute configurations of 1–5 were determined by comparing the experimental and calculated electronic circular dichroism (ECD) spectra. For 6 and 7, the same chirality was assigned according to their biosynthetic similarities with the other compounds. The successful assignment of some Cotton effects was achieved by utilizing DFT calculations using simple model compounds. The plausible biosynthesis of 1–7 was also discussed on the basis of the structural commonality and general cyclohumulanoid biosynthesis. Compounds 2a and 5 were found to simultaneously induce hyphal swelling and branching at 5.0 μg/mL against a test fungus Cochliobolus miyabeanus.

Isolation and structural elucidation of novel fusicoccan dehydroxypericonicin A from Roussoella sp.

A potent antifungal fusicoccane dehydroxypericonicin A (1) was isolated from Roussoella sp. along with known allantofuranone (2). The relative structure of 1 was fully elucidated by NMR spectroscopic manner. The suggested relative structure was confirmed by DFT (density functional theory)-based 13C NMR chemical shift calculations. The absolute configuration was investigated by a spectral comparison of the experimental ECD (electronic circular dichroism) spectrum with that based on the DFT calculations.

Beryllium (II) Chloride Complexes with Phosphoryl Ligands: A DFT Study

Beryllium complexes of the types [BeCl2L2] (L = (Me2N)3P(O) (1), (Me2N)2P(O)F (2), Me2NP(O)F2 (3) and P(O)F3 (4)) have been theoretically studied by means of DFT geometry optimization and NMR chemical shift calculations (B3LYP/6-31G(d)). A good correlation was found between calculated and experimental data for complex 2. On going from complex 1 to 4, the Be-L bond underwent considerable lengthening, while that of Be-Cl was shortened (Be-O: 1.646 in 1 vs. 1.740 A° in 4; Be-Cl: 2.043 in 1 vs. 1.953 A° in 4). In the same way, the Be-O-P bond angle was found to decrease from 135° for 1 to 124° for 4. The trends are in good agreement with the calculated metal-ligand binding energies of complexes 1-4. Interestingly, the structural changes are accompanied by increased 9Be chemical shifts towards higher frequencies as the Me2N groups in the ligand are substituted by fluorine atoms. The results were compared to corresponding complexes with tin (IV) chloride, [SnCl4L2]. The theoretical data showed that the use of the 6-31G* basis set could efficiently predict the 9Be NMR chemical shifts in the complexes [BeCl2L2].

Oxygenated Theonellastrols: Interpretation of Unusual Chemical Behaviors Using Quantum Mechanical Calculations and Stereochemical Reassignment of 7α-Hydroxytheonellasterol

A total of eight new oxygenated 4-exo-methylene sterols, 1–8, together with one artifact 9 and six known sterols 11–16, were isolated from the marine sponge Theonella swinhoei collected from the Bohol province in Philippines. Structures of sterols 1–8 were determined from 1D and 2D NMR data. Among the sterols, 8α-hydroxytheonellasterol (4) spontaneously underwent an allylic 1,3-hydroxyl shift to produce 15α-hydroxytheonellasterol (9) as an artifact; this was rationalized by quantum mechanical calculations of the transition state. In addition, the 1,2-epoxy alcohol subunit of 8α-hydroxy-14,15-β-epoxytheonellasterol (5) was assigned using the Gauge-Independent Atomic Orbital (GIAO) NMR chemical shift calculations and subsequent DP4+ analysis. Finally, comparison of the 13C chemical shifts of isolated 7α-hydroxytheonellasterol (6) with the reported values revealed significant discrepancies at C-6, C-7, C-8, and C-14, leading to reassignment of the C-7 stereochemistry in the known structure.

Synthesis of azabenziporphyrinoids by SN Ar reactions

While most of porphyrins and related macrocycles have been synthesized by classical acid-catalyzed condensation and oxidation reactions, nucleophilic aromatic substitution reactions have recently emerged as a new protocol to construct novel porphyrinoids. [Formula: see text]-Dibromotripyrrin 3 was developed as a useful building block composed of three pyrrolic segments and two meso-carbons, which was allowed to react with various nucleophiles. Herein, we applied this strategy to synthesize carbaporphyrinoids containing two nitrogen atoms at the meso-positions. Reaction of [Formula: see text]-dibromotripyrrin 3 with meta- and para-phenylenediamine gave diazabenziporphyrins 8 and 9in good yields. Their oxidized species 12 and 13 were generated by facile oxidation with lead dioxide. While diaza-meta-benziporphyrin 12 exhibited nonaromatic characteristics, diaza-para-benziporphyrin 13 was revealed to be aromatic in view of [Formula: see text]H NMR, bond-alternation, and nucleus-independent-chemical-shift calculations. Curiously, aza-meta-benzicorrole 11 was obtained in a low yield by intramolecular cyclization reaction of [Formula: see text]-anilino-[Formula: see text]-bromotripyrrin with potassium carbonate.