Suzuki-Miyaura Cross-Coupling Reactions of Tetrahydroxanthones and 4-Chromanone Lactones to Heteromeric Biaryls

Enantioselective total synthesis of parnafungin A1 and 10a-epi-hirtusneanine

The first and enantioselective total synthesis of the heterodimeric biaryl antifungal natural product parnafungin A1 as well as complex biaryl tetrahydroxanthone 10a-epi-hirtusneanine is accomplished, by employing cross-coupling through the benzoxaborole strategy to construct their sterically hindered biaryl cores. Besides the powerful Suzuki-Miyaura cross-coupling, the synthesis of parnafungin A1 also features a highly diastereoselective oxa-Michael addition to construct a tetrahydroxanthone skeleton, and an effective Zn-mediated reductive cyclization-Mitsunobu sequence to furnish the isoxazolidinone structure. Key innovations in total synthesis of 10a-epi-hirtusneanine include the employment of DTBS protection for functional group manipulation on the tetrahydroxanthone skeleton, stereoselective methylations, and complete reversal of the stereochemistry of the C5-hydroxy group using oxidation/Evans-Saksena reduction, as well as the strategy of preparing both complex tetrahydroxanthone monomers from the same chiral intermediate 25.

Synthesis and Anticancer Activity of Structure Simplified Naturally-Inspired Dimeric Chromenone Derivatives

Select dimeric chromenones exhibit low micromolar cyctotoxicity toward lymphoma and leukemia cell lines, L5178Y and HL60, respectively. The bioactive dimeric chromenones were identified from a focused library of structurally-simplified derivatives of naturally-occurring dimeric chromenones and tetrahydroxanthones that was prepared as part of this study. The simple dimeric chromenone scaffolds contain no stereogenic centers, are easily synthesized, and may be utilized as lead compounds in cancer research and drug discovery.

Enantioselective Total Synthesis of Chromanone Lactone Homo- and Heterodimers

A one pot borylation/Suzuki-Miyaura reaction of the 4-bromochromanone lactones 21 and 23, respectively, followed by cleavage of the methyl ether moieties gave the homodimeric chromanone lactones 10 and 11. Reaction of a 1:1 mixture of 21 and 23 under otherwise identical conditions gave a 1:1:2-mixture of the two homodimers 10 and 11 and the heterodimer 12. This is the first example of the preparation of a heterodimeric chromanone lactone. For the enantioselective synthesis of the starting material, phenol 17 was transformed into the chromane 18 using a Wacker-type cyclisation with 99 % ee and 80 % yield.

Enantioselective Total Synthesis of Blennolide H and Phomopsis-H76 A and Determination of Their Structure

This work reports on the enantioselective total synthesis of the two dimeric natural chromanone lactones phomopsis-H76 A (5) and blennolide H (6). Both syntheses could be achieved from chromane 11, which was obtained by an enantioselective Wacker-type cyclization with >99 % ee. The dimerization of the corresponding monomers was performed using a palladium-catalyzed Suzuki reaction. Moreover, within this work it was possible to revise the absolute configuration of phomopsis-H76 A and determine the relative as well as absolute configuration of blennolide H.