1. Total Synthesis of Cyrneine A Elangovan Elamparuthi, Cindy Fellay, Markus Neuburger, and Karl Gademann* Department of Chemistry, University of Basel National Centre of Competence in Research “Chemical Biology” Switzerland Angew. Chem. Int. Ed. 2012, 51, 1 – 4 6/14/2016

2. The terpenoids sometimes called isoprenoids, are a large and diverse class of naturally occurring organic chemicals similar to terpenes, derived from five-carbon isoprene units assembled and modified in thousands of ways.organic chemicalsterpenes isoprene Most are multicyclic structures that differ from one another not only in functional groups but also in their basic carbon skeletons. These lipids can be found in all classes of living things, and are the largest group of natural products.functional groupslipids Structure and classification TerpenesTerpenes are hydrocarbons resulting from the combination of several isoprene units. Terpenoids can be thought of as modified terpenes, wherein methyl groups have been moved or removed, or oxygen atoms addedhydrocarbonsisoprenemethyl groupsoxygen The terpenoids can be classified according to the number of isoprene units used: Hemiterpenoids, 1 isoprene unit (5 carbons) Monoterpenoids, 2 isoprene units (10C) Sesquiterpenoids, 3 isoprene units (15C) Diterpenoids, 4 isoprene units (20C) Sesterterpenoids, 5 isoprene units (25C) TriterpenoidsTriterpenoids, 6 isoprene units (30C) TetraterpenoidsTetraterpenoids, 8 isoprene units (40C) PolyterpenoidPolyterpenoid with a larger number of isoprene units

3. The cyathane diterpene natural products are isolated from a diverse variety of fungi, sponges, and fruiting plants. However, despite their myriad natural sources, all are unified by the presence of a characteristic 5–6–7 tricarbocyclic fused core structure Within this class of natural products can be found the cyathins, the allocyathins, the erinacines, the sarcodonins, the scabronines, the striatals, the cyanthiwigins, and the cyafrins, all of which display the conserved carbon scaffold of the cyathane skeleton. Of the twenty carbons that comprise this cyathane framework, the C(6) and C(9) carbons present all-carbon quaternary stereocenters, which bear angular methyl groups at the points of ring fusion. Overview of the cyathane diterpenoids 6/14/2016

4. Almost all of the compounds within the cyathane class display these methyl groups with an anti relative stereochemical relationship, though the cyanthiwigin natural products possess a syn arrangement. The cyathane core structure is additionally characterized by the presence of an isopropyl side chain at C(3) and an exocyclic carbon atom connected to C(12). 6/14/2016

5. The biological activities of the cyathane natural products vary widely among the different molecules within the class. Many of these diterpene compounds, such as the previously discussed (-)-cyathin A3 and (+)-allocyathin B3, possess antibiotic or antimicrobial activity. Indeed, almost all of the subcategories of cyathane molecules display mild activity in this regard. In addition to serving an antibiotic function, some members of the cyanthiwigin compounds have displayed limited cytotoxic activity against human primary tumor cells, as well as P388 murine leukemia cells and A549 lung tumor cells. However, the most significant biological activity reported among these diterpenoid molecules is their powerful ability to encourage the synthesis of Nerve Growth Factor (NGF). Both the erinacine and the scabronine natural products have displayed considerable potency in the stimulation of NGF synthesis, a capacity that implicates their potential as therapeutic agents to treat neurodegenerative ailments such as Alzheimer’s or Parkinson’s disease. Bioactivity 6/14/2016

6. . Introduction The enhancement of cognitive processes and the improvement of memory by drugs or natural products (sometimes called brain doping) is increasingly performed in our knowledge-based society and is, therefore, a controversial topic. The identification of such cognitive enhancers is the goal of many research groups, in particular as such drugs could open up new therapeutic avenues for the treatment of neurodegenerative diseases. A hallmark of such diseases is neuritic atrophy, and compounds inducing or enhancing neurite outgrowth present interesting lead structures. During our research efforts on the synthesis and biological evaluation of such compounds. Cyrneine A (1) is a member of the cyathane diterpenes, of which several successful synthetic strategies have been published.(Review: a) J. A. Enquist, Jr., B. M. Stoltz, Nat. Prod. Rep. 2009,26, 661 – 680) cyathane diterpenes, cyrneines A (1) was isolated from the mushroom Sarcodon cyrneus.

7. The stimulating activity on neurite outgrowth of cyrneines was evaluated. Rat pheochromocytoma cells (PC12), used as a model system of neuronal differentiation, were cultured with cyrneine A (100 microM), or NGF (100 ng/ml) for 24 h. Interestingly, cyrneines A significantly promoted neurite outgrowth in addition to NGF as a positive control. (Planta Med. 2006, 72, 819 – 823). Cyrneine A (1) features a tricyclic 5-6-7 ring system containing a hexatrienal unit. In addition, the quaternary stereogenic centers at C6 and C9 with the angular methyl groups pose a synthetic challenge, which is complemented by the two neighboring stereogenic centers. We opted for a convergent synthetic strategy, which would join the five- and seven membered rings through a reductive Knoevenagel condensation and a Heck cylization. Additional interesting steps would include a Yamamoto ring expansion reaction and a palladium-mediated reductive carbonylation

8. 6/14/2016 Synthesis of Cyrneine A, prepared from commercially available (-)(R)-Carvone

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14. X-ray crystal structure analysis : cyrneine A (1)

15.  We have reported herein the first total synthesis of cyrneine A (1).  Salient features of this route include a reductive Knoevenagel/Heck cyclization strategy, a remarkably regioselective reductive desymmetrization, a ring expansion by a carbene rearrangement, as well as a reductive, palladium mediated carbonylation.  The overall synthesis proceeds in 24 steps and 1.1 % overall yield.  Crystal-structure analysis of synthetic cyrneine A (1) led to the definitive establishment of the structure of this natural product.  Biological investigations regarding the Rac1-dependent induction of neurite outgrowth are currently underway. 6/14/2016 Conclusion

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