A ring-closing metathesis approach to the bicyclo[4.3.1]decane core of caryolanes

Total synthesis of (+)-ent-vetiverianine a via Lewis acid-mediated cyclization

We describe the first total synthesis of (+)-ent-vetiverianine A, which exhibits a 5/6/6-fused tricyclic structure, with the longest linear sequence of 14 steps, and in 12% overall yield.

Cobalt-Catalyzed [6 + 2] Cycloaddition of Alkynes with 1,3,5,7-Cyclooctatetraene as a Key Element in the Direct Construction of Substituted Bicyclo[4.3.1]decanes

A new, effective catalytic system based on Co(acac)₂ has been developed for [6 + 2] cycloaddition of terminal alkynes to 1,3,5,7-cyclooctatetraene to give substituted bicyclo[4.2.2]deca-2,4,7,9-tetraenes in high yields (68-85%). The electrophilic activation of double bonds in the bicyclic products with m-CPBA is an efficient method for the synthesis of substituted bicyclo[4.3.1]deca-2,4,8-triene-7,10-diols, which form the key structural moieties of numerous natural biologically active compounds. The structures of the obtained compounds were reliably proven by modern spectral methods and X-ray diffraction. The mechanism of the discovered rearrangement was studied both using deuterium-labeled bicyclo[4.2.2]deca-2,4,7,9-tetraenes and utilizing quantum chemical calculations. The obtained substituted bicyclo[4.3.1]deca-2,4,8-triene-7,10-diols and their keto derivatives showed high antitumor activity in vitro against Hek293, Jurkat, K562, and A549 tumor cell lines.

Functional Analysis of Amorpha-4,11-Diene Synthase (ADS) Homologs from Non-Artemisinin-Producing Artemisia Species: The Discovery of Novel Koidzumiol and (+)-α-Bisabolol Synthases

The production of artemisinin, the most effective antimalarial compound, is limited to Artemisia annua. Enzymes involved in artemisinin biosynthesis include amorpha-4,11-diene synthase (ADS), amorpha-4,11-diene 12-monooxygenase (CYP71AV1) and artemisinic aldehyde Δ(11)13 reductase (DBR2). Although artemisinin and its specific intermediates are not detected in other Artemisia species, we reported previously that CYP71AV1 and DBR2 homologs were expressed in some non-artemisinin-producing Artemisia plants. These homologous enzymes showed similar functions to their counterparts in A. annua and can convert fed intermediates into the following products along the artemisinin biosynthesis in planta These findings suggested a partial artemisinin-producing ability in those species. In this study, we examined genes highly homologous to ADS, the first committed gene in the pathway, in 13 Artemisia species. We detected ADS homologs in A. absinthium, A. kurramensis and A. maritima. We analyzed the enzymatic functions of all of the ADS homologs after obtaining their cDNA. We found that the ADS homolog from A. absinthium exhibited novel activity in the cyclization of farnesyl pyrophosphate (FPP) to koidzumiol, a rare natural sesquiterpenoid. Those from A. kurramensis and A. maritima showed similar, but novel, activities in the cyclization of FPP to (+)-α-bisabolol. The unique functions of the novel sesquiterpene synthases highly homologous to ADS found in this study could provide insight into the molecular basis of the exceptional artemisinin-producing ability in A. annua.