Synthesis of (+)-Epoxydon, (-)-Phyllostine, (-)-RKTS 33, and (-)-Parasitenone Featuring Selective Sulfonylation and Oxirane Ring Closure of Aldol Cyclization Products

Natural epoxyquinoids: isolation, biological activity and synthesis. An update

Epoxyquinoids are of continuing interest due to their wide natural distribution and diverse biological activities, including, but not limited to, antibacterial, antifungal, anticancer, enzyme inhibitory, and others. The last review on their total synthesis was published in 2017. Since then, almost 100 articles have been published on their isolation from nature and their biological profile. In addition, the review specifically considers synthesis, including total and enantioselective, as well as the development of shorter approaches for the construction of epoxyquinoids with complex chemical architecture. Thus, this review focuses on progress in this area in order to stimulate further research.

A Synthetic Approach to Several C7-Carbasugars via a Key Intramolecular Morita-Baylis-Hillman Reaction

A new synthetic strategy for C7-carbasugars is developed via an intramolecular Morita-Baylis-Hillman reaction, in which a substituted dial precursor prepared from d-mannose cyclizes smoothly in the presence of DMAP to afford polyhydroxylated cyclohex-1-enecarbaldehyde with good yield. By employment of the cyclization products as key intermediates, the first syntheses of carbasugar ester 1 and epicorepoxydon A, as well as practical syntheses of epoxydines B and C, (-)-MK7607, (-)-streptol, and (-)-gabosine E are achieved.

Practical synthesis of ECH and epoxyquinols A and B from (-)-shikimic acid

An efficient synthesis of ECH, epoxyquinols A and B, and two bioactive analogs EqM and RKTS-33 has been completed starting from (-)-shikimic acid. Rapid establishment of the desired epoxyquinol core is facilitated through a key allylic oxidation with high stereoselectivity, which is achieved by fine tuning the cyclohexene substrate structure and reaction conditions.

Novel Stereoselective Syntheses of (+)-Streptol and (-)-1-epi-Streptol Starting from Naturally Abundant (-)-Shikimic Acid

Novel highly stereoselective syntheses of (+)-streptol and (-)-1-epi-streptol starting from naturally abundant (-)-shikimic acid were described in this article. (-)-Shikimic acid was first converted to the common key intermediate by 11 steps in 40% yield. It was then converted to (+)-streptol by three steps in 72% yield, and it was also converted to (-)-1-epi-streptol by one step in 90% yield. In summary, (+)-streptol and (-)-1-epi-streptol were synthesized from (-)-shikimic acid by 14 and 12 steps in 29 and 36% overall yields, respectively.