Synthesis of Stereochemical Library of a Potent Antimalarial Monocerin Derivative and Its Stereochemical Revision

This study presents a total synthesis and revision of the stereochemical configuration of a potent antimalarial lead compound 2 possessing a benzo-pyranone framework, which was derived from the (+)-monocerin natural product of marine fungi, Exserohilum sp. Chiral hypervalent iodine(III)-catalyzed oxylactonization and late-stage O-methylation were highlights of the synthesis, which enabled access to the library of all possible eight stereoisomers of 2 for further understanding of stereochemical structure activity relationships (S-SARs).

Total Synthesis of Bipenicilisorin and Assignment of the Absolute Configuration

The first total synthesis of bipenicilisorin (1) isolated from Penicillium chrysogenum SCSIO 41001 via its monomer natural product, penicilisorin (2), was achieved. Penicilisorin was synthesized in four steps from a o-bromobenzaldehyde derivative via the Pd-catalyzed one-pot fluorocarbonylation/lactonization/β-elimination cascade reaction. Iodination of penicilisorin gave 7-iodopenicilisorin which was dimerized by Pd-catalyzed homodimerization to provide (±)-bipenicilisorin. The unknown absolute configuration of naturally occurring (+)-bipenicilisorin was examined by optical resolution of the (±)-synthetic bipenicilisorin and a comparison of experimental and theoretical electronic circular dichroism (ECD) spectra. These results support the absolute configuration of the natural product to be Sa. A cytotoxic activity test of (+)-and (-)-bipenicilisorin using A549 cells revealed that (+)-1 has a lower IC50 value than (-)-1.

Total Synthesis and Revision of Stereochemistry of a Natural Benzo[g]isochromene Stereodiad Isolated from Rubia philippinensis

This study presents a total synthesis and revision of the stereochemical configuration of the conformationally flexible natural product benzo[g]isochromene stereodiad alongside its diastereomeric counterparts. The highlights of the synthesis are the TiCl4-mediated diastereoselective aldol reaction, Pd-catalyzed lactonization, and Schmidt glycosidation. Our efforts using total synthesis disclosed herein proved that a previously assigned structure required revision.

Total Syntheses and Cytotoxicity Evaluation of Coryaurone A and Representative Analogues

The first total synthesis of coryaurone A, which was originally obtained from Psoralea corylifolia L., was achieved via an efficient route with the longest linear sequence of six steps from the commercially available 6-hydroxy-2H-benzofuran-3-one in 37% overall yield. A series of representative analogues were synthesized from the same starting material in 4-7 steps with overall yields of 27-56%. The cytotoxicities of these compounds against the leukemia cell line HL-60 and the colon cancer cell line SW480 were determined. Among them, compounds 12, 14, 21, and 27 exhibited different levels of cytotoxic activity, which were greater than the positive control cisplatin.

Asymmetric Total Synthesis of Amphirionin-2

A convergent route for the asymmetric total synthesis of potent anticancer polyketide natural product amphirionin-2 has been developed. Our initial synthetic trials revealed that the proposed structures of amphirionin-2 need to be revised consistent with a recent report of Fuwa et al., where the actual structure of amphirionin-2 was established. The key features of our synthesis comprised Sharpless asymmetric dihydroxylation, followed by cycloetherification, Wittig olefination, Julia-Kocienski olefination, and Crimmins propionate aldol reaction.

Marine natural products

This review covers the literature published between January and December in 2018 for marine natural products (MNPs), with 717 citations (706 for the period January to December 2018) referring to compounds isolated from marine microorganisms and phytoplankton, green, brown and red algae, sponges, cnidarians, bryozoans, molluscs, tunicates, echinoderms, mangroves and other intertidal plants and microorganisms. The emphasis is on new compounds (1554 in 469 papers for 2018), together with the relevant biological activities, source organisms and country of origin. Reviews, biosynthetic studies, first syntheses, and syntheses that led to the revision of structures or stereochemistries, have been included. The proportion of MNPs assigned absolute configuration over the last decade is also surveyed.

Annulations with Butenolides and Phthalides: New Entries to Isocoumarins, 3,4-Dihydroisocoumarins, and Benzofurans

The reactions of the anions of butenolides and substituted phthalides with sorbate esters and mono-epoxy sorbate esters furnish isocoumarins, 3,4-dihydroisocoumarins, and benzofurans. The yields range from 41% to 71%.

The crystal structure, Hirshfeld surface analysis and energy frameworks of 2-[2-(meth-oxy-carbon-yl)-3,6-bis-(meth-oxy-meth-oxy)phen-yl]acetic acid

In the title compound, C14H18O8, (I), the meth-oxy-carbonyl [-C(=O)OCH3] and the acetic acid [-CH2C(=O)OH] groups are inclined to the benzene ring by 79.24 (11) and 76.71 (13)°, respectively, and are normal to each other with a dihedral angle of 90.00 (13)°. In the crystal, mol-ecules are linked by a pair of O-H⋯O hydrogen bonds forming the familiar acetic acid inversion dimer. The dimers are linked by two C-H⋯O hydrogen bonds and an offset π-π inter-action [inter-centroid distance = 3.6405 (14) Å], forming layers lying parallel to the (10) plane. The layers are linked by a third C-H⋯O hydrogen bond and a C-H⋯π inter-action to form a supra-molecular framework.

Synthesis and Antimicrobial Evaluation of Side-Chain Derivatives based on Eurotiumide A

Side-chain derivatives of eurotiumide A, a dihydroisochroman-type natural product, have been synthesized and their antimicrobial activities described. Sixteen derivatives were synthesized from a key intermediate of the total synthesis of eurotiumide A, and their antimicrobial activities against two Gram-positive bacteria, methicillin-susceptible and methicillin-resistant Staphylococcus aureus (MSSA and MRSA), and a Gram-negative bacterium, Porphyromonas gingivalis, were evaluated. The results showed that derivatives having an iodine atom on their aromatic ring instead of the prenyl moiety displayed better antimicrobial activity than eurotiumide A against MSSA and P. gingivalis. Moreover, we discovered that a derivative with an isopentyl side chain, which is a hydrogenated product of eurotiumide A, is the strongest antimicrobial agent against all three strains, including MRSA.

A Synthesis of Dihydro Eurotiumide B via a Tandem Butenolide Annulation/Reductive Thiolation Reaction

Dihydro eurotiumide B was prepared from a 5-phenylthiobutenolide via a tandem annulation/reductive thiolation reaction.

Catalytic Asymmetric Cycloadditions between Aldehydes and Enolizable Anhydrides: cis-Selective Dihydroisocoumarin Formation

In the presence of a trityl-substituted cinchona alkaloid-based catalyst, homophthalic, aryl succinic, and glutaconic anhydride derivatives reacted with aromatic and aliphatic aldehydes to produce cis-lactones in up to 90:10 dr and 99% ee. A DFT study has shown how the catalyst is uniquely able to bring about the opposite sense of diastereocontrol to that usually observed.