Enantioselective 5-exo-Fluorocyclization of Ene-Oximes

The enantioselective 5-exo-fluorocyclization of ene-oxime compounds was demonstrated under phase-transfer catalysis. Although deprotonative fluorinations competed, the chemical yields and the ee values of the desired isoxazoline products were generally moderate to good. The absolute stereochemistry of the major isomer was determined to be S by comparison with the literature after transformation of the product to the corresponding iodinated isoxazoline.

Total Synthesis of PF1163B

A total synthesis of PF1163B has been achieved. The vinylogous Mukaiyama aldol reaction of ketene silyl N,O-acetal 6 (ent-6) mediated by excess TiCl4 proceeded with saturated aldehydes to give adduct 10 in moderate yield with moderate stereoselectivity. The major isomer is the diastereomer that was provided by using one equivalent of TiCl4. The Birch reduction of α,β-unsaturated imide 4, possessing a less hindered side chain, gave 12 in good stereoselectivity by employing 2-isopropylbenzimidazole as a bulky proton source. After elongation of the carbon chain and connection with the amino acid part, we accomplished a total synthesis of PF1163B. These methods constitute a concise synthetic route to obtain polyketides as well as depsipeptides.

Quantification of Caffeoylquinic Acids in Coffee Brews by HPLC-DAD

The influence of different brewing conditions on the concentration of the main caffeoylquinic acids (3-caffeoylquinic acid (3-CQA), 4-caffeoylquinic acid (4-CQA), and 5-caffeoylquinic acid (5-CQA)) was investigated. For this purpose, twenty-four coffee brews were extracted and analyzed using HPLC-DAD at 325 nm. Our findings demonstrate the great impact of brewing techniques on the caffeoylquinic acids (CQAs) content. The major isomer was 3-CQA, accounting for about 50% of the total CQAs, followed by 5-CQA and 4-CQA, accounting for about 24–36% for each one. The total content of CQAs was in the range of 45.79 to 1662.01 mg/L, found in iced cappuccino and pod espresso, respectively. In conclusion, this study demonstrates that coffee brews, in particular those prepared using pressurized methods, can be considered as the potential sources of antioxidants such as CQAs.

Synthesis of a New Class of Molecule Li+@C60O–(OH)7 as a “Cation-Encapsulated Anion Nanoparticle” by Multihydroxylation of Li-Encapsulated Fullerene

ABSTRACTTreatment of [Li+@C60](PF6–) with 30% fuming sulfuric acid and subsequent hydrolysis gave hydroxylated derivative Li+@C60O–(OH)7. Its structure was deduced by IR, NMR, MALDI-TOF/FAB MS, and elemental analysis. Notably, the reaction of [Li+@C60](PF6–) was site-selective, giving a single major isomer (ca. 70%) with two minor isomers, in marked contrast to the case of empty C60. Furthermore, the results clearly indicate that the internal Li cation was strongly shielded by the surface dipolar hydroxyl groups, and thus it appears that the properties of endohedral fullerenes can be controlled by the external modification of the fullerene cage. Whereas Li+@C60 is relatively insoluble, Li+@C60O–(OH)7 was found to be highly soluble in polar solvents such as DMSO and DMF. The increased solubility is especially desirable for biological/medicinal assays and applications in such research fields.

Synthetic and Computational Studies on the ABC Trioxadispiroketal Subunit of the Marine Biotoxin Azaspiracid-1

The trioxadispiroketal residue in the marine biotoxin azaspiracid-1, which exists in a configuration capable of exhibiting a double anomeric effect, is believed to be the thermodynamically most stable bis-spiroketal diastereomer. In order to get insight into how structural factors affect this equilibrium, a simplified ABC trioxadispiroketal analog of azaspiracid-1 was synthesized and subjected to equilbration and computational studies. Compound 7, which represents a double anomeric effect was obtained as the major isomer, together with diastereomers 14 and 15, in a respective ratio of 62:22:16. DFT calculations for 7, 14 and 15 qualitatively matched this observation. These results suggest that while a double anomeric effect may play a major role in the stability of the trioxadispiroketal configuration in the more complex natural product, the substitution pattern of the C ring is also a contributing factor.