Synthesis and Determination of the Absolute Configuration of Fugomycin and Desoxyfugomycin: CD Spectroscopy and Fungicidal Activity of Butenolides

Anti-inflammatory and α-Glucosidase Inhibitory Activities of Labdane and Norlabdane Diterpenoids from the Rhizomes of Amomum villosum

A new tetranorditerpenoid (1), two new labdane diterpenoids (2, 3), and nine known analogues (4-12) were isolated from the rhizomes of Amomum villosum var. xanthioides. Compound 1 is an unprecedented rearranged tetranorlabdane diterpenoid, featuring a 6/6/5 fused tricarbocyclic skeleton with an α,β-unsaturated cyclopentenone unit, while 2 is a structurally rare labdane diterpenoid carrying a five-membered cyclic anhydride moiety. Their structures and absolute configurations were established on the basis of spectroscopic data and the experimental and calculated ECD data. Compound 4 showed inhibitory activity against nitric oxide production, with an IC₅₀ value of 2.4 μM, and also inhibited α-glucosidase activity (IC₅₀ = 10.0 μM).

Bioactive polyketides from the mangrove endophytic fungi Phoma sp. SYSU-SK-7

Five new polyketides, colletotric B (2), 3-hydroxy-5-methoxy-2,4,6-trimethylbenzoic acid (3), colletotric C (4), chaetochromone D (6) and 8-hydroxy-pregaliellalactone B (9), together with four known analogues (1, 5 and 7-8) were isolated from the mangrove endophytic fungus Phoma sp. SYSU-SK-7. Their structures were elucidated by analysis of extensive spectroscopic data and mass spectrometric data. Compounds 1-2 showed strong antimicrobial activity against the P. aeruginosa, MRSA and C. albicans with the MIC values in the range of 1.67-6.28 μg/ml. Furthermore, Compounds 1-5 also exhibited significant α-glucosidase inhibitory activity with the IC₅₀ values in the range of 36.2-90.6 μM. Compound 7 was found to inhibited radical scavenging activity against DPPH with the EC₅₀ value of 11.8 μM.

Thiosquaramide-catalysed asymmetric double Michael addition of 2-(3H)-furanones to nitroolefines

2,2,4-Trisubstituted butenolides bearing a quaternary stereogenic center were smoothly constructed with excellent stereoselectivities under mild conditions.

Gold Catalyzed Multicomponent Reactions beyond A³ Coupling

The preparation of complex architectures has inspired the search for new methods and new processes in organic synthesis. Multicomponent reactions have become an interesting approach to achieve such molecular diversity and complexity. This review intends to illustrate important gold-catalyzed examples for the past ten years leading to interesting skeletons involved in biologically active compounds.

Effect of different substituents on the one-pot formation of 3,4,5-substituted furan-2(5H)-ones: a kinetics and mechanism study

This work focused on the effects of temperature and different para-substituted anilines on the activation parameters and kinetics of the synthesis reaction of 3,4,5-substituted furan-2(5H)-ones which were studied spectrally at different temperatures in formic acid.

Circular dichroism and optical rotation of lactamide and 2-aminopropanol in aqueous solution

The performance of implicit and explicit solvent models (polarizable continuum model (PCM) and microsolvation with positions of water molecules obtained either from molecular dynamics (MD) simulations or quantum mechanical geometry optimization) for calculations of electronic circular dichroism (CD) and optical rotation (OR) is examined for two polar and flexible molecules: lactamide and 2-aminopropanol. The vibrational structure of the CD spectrum is modeled for lactamide. The results are compared with the newly obtained experimental data. The signs of the bands are correctly reproduced using all three methods under investigation and the CAM-B3LYP functional for the CD spectrum of lactamide, but not for 2-aminopropanol. The sign of the calculated optical rotation is correctly predicted by means of PCM, but its magnitude is somewhat underestimated in comparison with experiment for lactamide and overestimated for 2-aminopropanol. To some extent it is rectified by employing explicit hydration. Overall, microsolvation with geometry optimization seems more cost-effective than classical MD, but this is likely to be a consequence of inadequate classical potential and electronic structure model.

Empirical correction of nondynamical correlation energy for density functionals

To provide an efficient means to address nondynamical correlation, an empirical correction for single and double hybrid density functionals has been formulated. The correction utilizes the highest doubly occupied, lowest unoccupied, and singly occupied generalized Kohn-Sham orbitals and, for potential energy curves, a few additional strongly correlated orbitals. Utilizing proposed nondynamical correlation corrections, hybrid BLYP predicted potential energy curves that fit well to those obtained by ab initio multireference methods for the torsional rotation of ethylene and the automerization of cyclobutadiene. The empirical nondynamical correlation corrections, calculated at the transition structures, also reduce the overall errors of B2K-PLYP for the DBH24 and BH76 barrier height data sets. The proposed empirical correction can efficiently enhance the utility of both single and double hybrid density functionals for chemical situations with moderate to significant nondynamical correlation.

Synthesis and in vitro antitumor activity of new butenolide-containing dithiocarbamates

Three series of butenolide-containing dithiocarbamates were designed and synthesized. Their anti-tumor activity in vitro was evaluated. Among them compound I-14 exhibited broad spectrum anti-cancer activity against five human cancer cell lines with IC(50) <30 μM. Structure-activity relationship analysis showed that the introduction of dithiocarbamate side chains on the C-3 position of butenolide was crucial for anti-tumor activity.

Chiral aromatase and dual aromatase-steroid sulfatase inhibitors from the letrozole template: synthesis, absolute configuration, and in vitro activity

To explore aromatase inhibition and to broaden the structural diversity of dual aromatase-sulfatase inhibitors (DASIs), we introduced the steroid sulfatase (STS) inhibitory pharmacophore to letrozole. Letrozole derivatives were prepared bearing bis-sulfamates or mono-sulfamates with or without adjacent substituents. The most potent of the achiral and racemic aromatase inhibitor was 40 (IC 50 = 3.0 nM). Its phenolic precursor 39 was separated by chiral HPLC, and the absolute configuration of each enantiomer was determined using vibrational and electronic circular dichroism in tandem with calculations of the predicted spectra. Of the two enantiomers, ( R)-phenol ( 39a) was the most potent aromatase inhibitor (IC 50 = 0.6 nM, comparable to letrozole), whereas the ( S)-sulfamate, ( 40b) inhibited STS most potently (IC 50 = 553 nM). These results suggest that a new structural class of DASI for potential treatment of hormone-dependent breast cancer has been identified, and this is the first report of STS inhibition by an enantiopure nonsteroidal compound.

Determination of Absolute Configuration Using Density Functional Theory Calculations of Optical Rotation and Electronic Circular Dichroism: Chiral Alkenes

In principle, the absolute configuration (AC) of a chiral molecule can be deduced from its optical rotation (OR) and/or its electronic circular dichroism (ECD). In practice, this requires reliable methodologies for predicting OR and ECD. The recent application of ab initio time-dependent density functional theory (TDDFT) to the calculation of transparent spectral region OR and ECD has greatly enhanced the reliability with which these phenomena can be predicted. TDDFT calculations of OR and ECD are being increasingly utilized in determining ACs. Nevertheless, such calculations are not perfect, and as a result, ACs determined are not 100% reliable. In this paper, we examine the reliability of the TDDFT methods in the case of chiral alkenes. Sodium d line specific rotations, [alpha]D, are predicted for 26 conformationally rigid alkenes of known AC, ranging in size from 5 to 20 C atoms, and with [alpha]D values in the range of 0-500. The mean absolute deviation of predicted [alpha]D values from experimental values is 28.7. With one exception, beta-pinene, the signs of [alpha]D are correctly predicted. Errors in calculated [alpha]D values are approximately random. Our results define a "zone of indeterminacy" within which calculated [alpha]D values cannot be used to determine ACs with >95% confidence. TDDFT ECD spectra are predicted for eight of the alkenes and compared to experimental spectra. Agreement ranges from modestly good to poor, leading to the conclusion that TDDFT calculations of ECD spectra are not yet of sufficient accuracy to routinely provide highly reliable ACs. TDDFT OR calculations for two conformationally flexible alkenes, 3-tert-butylcyclohexene and trans-4-carene, are also reported. For the former, predicted rotations are incorrect in sign over the range 589-365 nm. It is possible that the AC of this molecule has been incorrectly assigned.

Enantioselective nonsteroidal aromatase inhibitors identified through a multidisciplinary medicinal chemistry approach

To identify enantioselective nonsteroidal aromatase inhibitors, a multidisciplinary medicinal chemistry approach was pursued. First, our earlier CoMFA model [Bioorg. Med. Chem. 1998,6, 377-388] was extended taking purposely into account previously discovered enantioselective aromatase inhibitors. The 3D QSAR model was then exploited to design chiral ligands, whose configurational assignment was obtained, after HPLC separation, by means of a combination of circular dichroism measurements and time dependent density functional calculations. Finally, the new enantiomeric inhibitors were separately tested to ascertain both their potency against the cytochrome P450 aromatase (CYP19; EC 1.14.14.1), and their selectivity relative to another enzyme of the P450 family. A satisfactory agreement between experimental and predicted data allowed us to assert that a properly built "enantioselective CoMFA model" might constitute a useful tool for addressing enantioselective ligands design.

Enantioselective Syntheses and Configuration Assignments of γ-Chiral Butenolides fromPlagiomnium undulatum: Butenolide Synthesis from Tetronic Acids

Both enantiomers of the gamma-chiral alpha,beta-dimethylated butyrolactones nat-1 and nat-2 from the moss Plagiomnium undulatum were synthesized stereoselectively through butenolides and tetronic acids, respectively. The configuration of the natural products was determined by GLC comparisons with mono(3-O-acetyl-6-O-tert-butyldimethylsilyl-2-O-methyl)hexakis(6-O-tert-butyldimethylsilyl-2,3-di-O-methyl)-beta-cyclodextrin as a stationary phase.