The Total Synthesis and Structural Assignment of Hexaketide Xylarinol B and its C1′-Epimer

Total Synthesis of (+)-Petromyroxol, (-)-iso-Petromyroxol, and Possible Diastereomers

The total synthesis of (+)-petromyroxol (1) and its seven diastereomers including the (-)-iso-petromyroxol (2) is described. The employed strategy involves the use of easily available C5-epimeric epoxides 5 and 5' and nonselective anomeric C1-allylation, proceeding with or without inversion at C2, thereby giving the possibility of synthesizing all possible diastereomers. Extensive two-dimensional (2D) NMR analyses of all eight diastereomers have been carried out to assign the chemical shifts of the central carbons and the corresponding attached hydrogens and to learn how the C/H-chemical shifts of the tetrahydrofuran ring were influenced by the adjacent centers.

New Polyketides from the Marine-Derived Fungus Letendraea sp. 5XNZ4-2

Marine-derived fungi have been reported to have great potential to produce structurally unique metabolites. Our investigation on secondary metabolites from marine-derived fungi resulted in the isolation of seven new polyketides (phomopsiketones D–G (1–4) and letendronols A–C (5–7)) as well as one known xylarinol (8) in the cultural broth of Letendraea sp. Their structures and absolute configurations were elucidated using a set of spectroscopic and chemical methods, including HRESIMS, NMR, single-crystal X-ray diffraction, ECD calculation, and a modified version of Mosher’s method. Compound 2 showed weak inhibition against nitric oxide production in lipopolysaccaride-activated macrophages with an IC₅₀ value of 86 μM.

Total Synthesis of (±)-Allocolchicine and Its Analogues Using Co-Catalyzed Alkyne [2 + 2 + 2]-Cyclotrimerization

The total synthesis of (±)-allocolchicine has been completed by employing cobalt-catalyzed alkyne [2 + 2 + 2]-cyclotrimerization as the key reaction. The essential diyne has been synthesized from easily available 3,4,5-trimethoxybenzaldehyde following simple chemical transformations. In general, the cycloaddition gave a mixture of C(9) and C(10) isomers thus allowing the synthesis of both allocolchicine and its C(10)-carboxylate. Because this cycloaddition was employed at the penultimate stage, it allowed the synthesis of various analogues having the diverse functionality at C(9) and/or C(10) of ring C.

α-Glucosidase Inhibitors from Malbranchea flavorosea

From an extract prepared from the grain-based culture of Malbranchea flavorosea two new polyketides, namely, 8-chloroxylarinol A (1) and flavoroseoside (2), along with the known compounds xylarinol A (3), xylarinol B (4), massarigenins B and C (5 and 6), and clavatol (7), were isolated. The structures of 1 and 2 were elucidated using spectroscopic methods and corroborated by single-crystal X-ray diffraction analysis. In the case of compound 2 the absolute configuration at the stereogenic centers was established according to the method of Flack. In addition, the X-ray structure of compound 6 is reported for the first time. Compounds 3, 4, and 6 significantly inhibited yeast α-glucosidase. Compound 6 also inhibited the postprandial peak during an oral sucrose tolerance assay when tested in vivo, using normal and NA/STZ-induced hyperglycemic mice.