̽����ѡ

The first total synthesis of (−)-mucosin (6), an unusual marine hydrindane natural product incorporating a prostaglandin-like submotif, has been achieved. As a result of the campaign, three of the four all-carbon stereocenters in the purported structure 1 have been revised. Of particular note is the excellent control over β-chirality in conjugate addition to ester (−)-22 and the facial selectivity in the subsequent protonation of an intermediate silyl ketene acetal.

The two ar-bisabol sesquiterpenoids (+)-sielboldianin A (1) and (+)-sielboldianin B (2) were isolated from the stem bark of the plant Fraxinus sielboldiana and belong to a medicinally interesting class of natural products used in traditional Chinese medicine. Herein the total synthesis of the proposed structure of (+)-sielboldianin A (1) is reported using an organocatalyzed enantioselective bromolactonization protocol. X-ray analysis of a key intermediate together with specific rotation values and NOESY data of the synthesized product enabled the revision of the absolute configuration of the natural product (+)-sielboldianin A to (7R,10R). Studies on the antioxidant effects using two cell-based assays were conducted. These studies revealed that the enantiomer of 1 exhibited antioxidant effects with IC50 values of 18 ± 3 μM in a cellular lipid peroxidation antioxidant activity assay. Moreover, (−)-1 showed strong protective effects against reactive oxygen species in a cell-based antioxidant activity assay (IC50 = 31 ± 5 μM). In addition, the two ar-sesquiterpenoids (−)-boivinianin B and (−)-gossoronol showed no effect in either assay. No cytotoxic activity in the K562 cancer cell line was observed for the three sesquiterpenoids tested (IC50 > 50 μM).

Versatile methods for the high-yield syntheses of new cyclometalated gold(III) complexes are described. Mono- or dialkylated or arylated gold(III) complexes are selectively obtained from reaction of Au(OCOCF3)2(tpy) (tpy = 2-(p-tolyl)pyridine) with either RMgX or RLi, respectively. Specifically, AuMe2(tpy) and AuPh2(tpy) were prepared with the respective lithium reagents, and AuBrMe(tpy), AuBrEt(tpy), and AuBrPh(tpy) were prepared with Grignard reagents. The molecular structures of compounds Au(OCOCF3)2(tpy) and AuMe2(tpy) were determined by single crystal X-ray diffraction.

Abstract: 2-Substituted N-methoxy-9-methyl-9H-purin-6-amines were synthesized either from their corresponding 6-chloro-9-methyl-9H-purines or 2-chloro-N-methoxy-9-methyl- 9H-purin-6-amine. Great diversity in the amino/imino tautomeric ratios was observed and calculated based on 1H NMR. The tautomers were identified by 1D and 2D 1H, 13C, and 15N NMR techniques, and showed significant variation both in 13C and 15N shift values. Comparison of the tautomeric ratios with Hammett F values revealed that as the field/inductive withdrawing abilities of the 2-substituent increased, the ratio of amino:imino tautomers was shifted toward the amino tautomer. Computational chemistry exposed the significance of hydrogen bonding between solvent and the compound in question to reach accurate predictions for tautomeric ratios. B3LYP/def2-TZVP density functional theory (DFT) calculations resulted in quantitatively more accurate predictions than when employing the less expensive BP86 functional. N-7-Alkylation of the 2-substituted N-methoxy-9-methyl-9H-purin-6- amines showed that when the field/inductive withdrawing ability of the 2-substituent reached a certain point the reactivity drastically dropped. This correlated with the atomic charges on N-7 calculated using a natural bond orbital (NBO) analysis. Biological screening of the final 2-substituted agelasine analogs indicated that the introduction of a methyl group in the 2-position is advantageous for antimycobacterial and antiprotozoal activity, and that an amino function may improve activity against several cancer cell lines.

Ultraviolet (UV) protection is crucial for all living organisms as it can cause serious harm damaging the DNA of cells and leading to conditions such as cataracts, blindness and skin cancer. Many animals can either produce their own sunscreen compound or acquire it in their diet. Goose eyes contain a single, unknown component (“Compound X”) that dominates the UV absorbing profile of the goose eye chamber fluid and with its high absorbance functions as natural sunglasses for geese. The aim of this study was to identify “Compound X” using various established analytical techniques and methods, as well as develop a new one; the concept of temperature programming crystallization prior to single crystal X-ray diffractometric analysis for limited samples was explored. High performance liquid chromatography (HPLC)-UV analysis confirmed the presence of a single compound with a maximum absorption of 254 nm, implying the presence of an aromatic ring. MS analysis implied a molar mass of 149.05 g/mol, and presence of hydroxyl group and carbon chain containing methyl group. As the “Compound X” crystallized in the form of fibers, it was not possible to conduct single crystal X-ray diffraction (SCXRD) analysis on the available diffractometer. When using model compounds, crystals obtained with temperature programming were suitable for SCXRD analysis. Further experimentation with this technique may open possibilities for structure elucidation of the “Compound X” and other new compounds in small samples.