Total Synthesis of (+)-Clavolonine, (−)-Deacetylfawcettiine, and (+)-Acetylfawcettiine

Total Syntheses of Polycyclic Diterpenes Phomopsene, Methyl Phomopsenonate, and iso-Phomopsene via Reorganization of C-C Single Bonds

The first total syntheses of polycyclic diterpenes phomopsene (1), methyl phomopsenonate (2), and iso-phomopsene (3) have been accomplished through the unusual cascade reorganization of C-C single bonds. This approach features: (i) a synergistic Nazarov cyclization/double ring expansions in one-step, developed by authors, to rapid and stereospecific construction of the 5/5/5/5 tetraquinane scaffold bearing contiguous quaternary centers and (ii) a one-pot strategic ring expansion through Beckmann fragmentation/recombination to efficiently assemble the requisite 5/5/6/5 tetracyclic skeleton of the target molecules 1-3. This work enables us to determine that the correct structure of iso-phomopsene is, in fact, the C7 epimer of the originally assigned structure. Finally, the absolute configurations of three target molecules were confirmed through enantioselective synthesis.

Construction of the tetracyclic core of the Lycopodium alkaloid annotinolide C

A concise approach to the tetracyclic core of annotinolide C has been developed which contains two key reactions epoxidation/1,2-migration to construct an aza [6.5] spiro ring (A and B) and semireduction/cyclization to construct lactone ring D.

Deciphering the Biosynthetic Mechanism of Pelletierine in Lycopodium Alkaloid Biosynthesis

Pelletierine, a proposed building block of Lycopodium alkaloids (LAs), was demonstrated to be synthesized via the non-enzymatic Mannich-like condensation of Δ¹-piperideine and 3-oxoglutaric acid produced by two new type III PKSs (HsPKS4 and PcPKS1) characterized from Huperzia serrata and Phlegmariurus cryptomerianus, respectively. The findings provide new insights for further understanding the biosynthesis of LAs such as huperzine A.

Development of New Innovative Synthetic Organic Chemistry Using Lone Pairs of Oxygen Atoms

Oxygen atoms have a lone pair of electrons, so they have high chelation ability, high nucleophilic ability, stabilizing ability of adjacent cations, and take a chelate or oxocarbenium ion structure with Lewis acids and metals. I took advantage of these properties to develop three new reactions, 1) asymmetric synthesis of chiral quaternary carbon centers, 2) asymmetric synthesis using acetal functions, and 3) organic chemistry using acetal-type reactive salt chemical species, and applied them to biologically active natural products synthesis. New reactions described here are all innovative and useful for natural products synthesis. In particular, the first asymmetric synthesis of fredericamycin A, and concise asymmetric synthesis of anthracycline antibiotics, scyphostatin, (+)-Sch 642305, (-)-stenine, clavolonine, (+)-rubrenolide, (+)-rubrynolide, (+)-centrolobine, and decytospolide A and B, etc., are noteworthy. Furthermore, since reactions using acetal-type reactive salt chemical species allow the coexistence of functional groups that normally cannot coexist, the reactions using reactive salts have potential to change the retrosynthesis planned based on conventional reactions.

Three new Lycopodium alkaloids from Lycopodium japonicum

Three new Lycopodium alkaloids (1-3), together with 15 known alkaloids, were isolated from club moss Lycopodium japonicum. Their structures were determined by extensive spectroscopic analysis, including 1D and 2D NMR spectra. Compound 1 has an unusual β-oriented methyl group substituted at C-15 and an α-hydroxy cyclopentenone moiety. All new alkaloids were evaluated for the inhibition of T-type calcium channel.

Palhicerines A-F, Lycopodium alkaloids from the club moss Palhinhaea cernua

Four fawcettimine-type (palhicerines A-D, resp.) and two lycopodine-type (palhicerines E and F) Lycopodium alkaloids together with twenty known ones were isolated from the whole plant of Palhinhaea cernua. The structures and absolute configurations of the palhicerines A-F were determined by extensive spectroscopic methods, single-crystal X-ray diffraction analyses, chemical transformation, and electronic circular dichroism (ECD) calculations or induced electronic circular dichroism (IECD) spectra. Among the isolates, the new C/D-ring of the palhicerines A-C (trans-fused fawcettimine-type alkaloids) are rare, and each possesses a β-oriented C-16 methyl group and a distinctive tertiary methoxy group at C-13. Chemotaxonomy for differentiating species in the genus Palhinhaea is briefly discussed.

Obscurumines H-P, new Lycopodium alkaloids from the club moss Lycopodium obscurum

Seven new fawcettimine-type (1-7) and two new lycopodine-type (8 and 9) Lycopodium alkaloids, as well as 10 known compounds, were isolated from the club moss, Lycopodium obscurum L. The structures of obscurumines H-P (1-9) were determined based on high-resolution MS and 1D and 2D NMR data. Compounds 1 and 2 include a new skeleton that is formed via the linkage of C-9-N-2', which is rarely present in Lycopodium alkaloids. The in vitro acetylcholinesterase (AChE) inhibitory activity assay showed that 5 exhibited weak anti-AChE activity with an IC50 value of 81.0 μM. Compound 8 exhibited inhibition of the secretion of IL-2 in phytohemagglutinin (PHA) and phorbol myristate acetate (PMA) stimulated Jurkat cells, and the IC50 value was 17.2 μM.

Exceedingly Concise and Elegant Synthesis of (+)-Paniculatine, (-)-Magellanine, and (+)-Magellaninone

Starting from inexpensive (+)-pulegone as the chiral building block, a highly convergent synthesis of the unusual diquinane-based structures of (+)-paniculatine (1), (-)-magellanine (2), and (+)-magellaninone (3), has been achieved. This approach is based upon a tandem acylation-alkylation of ketoester 8 and palladium-catalyzed olefin insertion, oxidation, and hydrogenation for construction of the tetracyclic framework. This exceedingly concise strategy, requiring only 12-14 steps, is the shortest to date.

The first asymmetric total synthesis of lycoposerramine-R

The first asymmetric total synthesis of lycoposerramine-R was accomplished by a strategy featuring the stereoselective intramolecular aldol cyclization giving a cis-fused 5/6 bicyclic skeleton and a new method for the construction of the pyridone ring via the aza-Wittig reaction, thereby establishing the absolute configuration of the natural product.

Three new Lycopodium alkaloids from Lycopodium obscurum

Chemical investigation on the crude alkaloid portion of Lycopodium obscurum led to isolation of three new fawcettimine-type Lycopodium alkaloids, lycobscurines A-C (1-3), together with three known compounds. Their structures were determined by spectroscopic methods including HR-ESI-MS and NMR techniques. All compounds were tested in an assay for acetylcholinesterase inhibitory activity.

New Lycopodium alkaloids from Lycopodium obscurum

Three new Lycopodium alkaloids, obscurumines C-E (1–3), along with nine known compounds, were isolated from the club moss Lycopodium obscurum L. Structures of the new compounds were determined on the basis of their spectroscopic analysis and the relative configurations of 1 were established by X-ray crystallographic analysis. All the new isolates were tested for the acetylcholinesterase (AChE) inhibitory activity.

Toward a unified approach for the lycopodines: synthesis of 10-hydroxylycopodine, deacetylpaniculine, and paniculine

The enantioselective syntheses of 10-hydroxylycopodine, deacetylpaniculine, and paniculine have been accomplished through use of a common intermediate. Key steps in the synthetic sequence toward these lycopodium alkaloids include formation of the tricyclic core via a conformationally accelerated, intramolecular Mannich cyclization and an organocatalyzed, intramolecular Michael addition to form the C(7)-C(12) linkage.

Total synthesis of the Lycopodium alkaloid serratezomine A using free radical-mediated vinyl amination to prepare a β-stannyl enamine linchpin

Serratezomine A is a member of the structurally diverse class of compounds known as the Lycopodium alkaloids. The key supporting studies and successful total synthesis of serratezomine A are described in this account. Significant features of the synthesis include the first application of free radical mediated vinyl amination and Hwu's oxidative allylation in a total synthesis and an intramolecular lactonization via a transannular S(N)i reaction. Minimal use of protecting groups and the highly diastereoselective formation of a hindered, quaternary stereocenter using an umpolung allylation are also highlights from a strategy perspective. Observation of quaternary carbon epimerization via a retro-Mannich/Mannich sequence highlights the additional challenge presented by the axial alcohol at C8 in serratezomine A.

Ivorenolide A, an unprecedented immunosuppressive macrolide from Khaya ivorensis: structural elucidation and bioinspired total synthesis

Ivorenolide A (1), a novel 18-membered macrolide featuring conjugated acetylenic bonds and five chiral centers, was isolated from Khaya ivorensis. The structure of 1 was fully determined by spectroscopic analysis, single-crystal X-ray diffraction, and bioinspired total synthesis. Both compound 1 and its synthetic enantiomer 2 showed potent and selective immunosuppressive activity.

Collective synthesis of Lycopodium alkaloids and tautomer locking strategy for the total synthesis of (-)-lycojapodine A

The collective total synthesis of Lycopodium alkaloids (+)-fawcettimine (1), (+)-fawcettidine (2), (+)-alopecuridine (4), (-)-lycojapodine A (6), and (-)-8-deoxyserratinine (7) has been accomplished from a common precursor (15) based on a highly concise route inspired by the proposed biosynthesis of the fawcettimine- and serratinine-type alkaloids. An intramolecular C-alkylation enabled efficient installation of the challenging spiro quaternary carbon center and the aza-cyclononane ring. The preparation of the tricyclic skeleton as well as the establishment of the correct relative stereochemistry of the oxa-quaternary center were achieved by hydroxyl-directed SmI(2)-mediated pinacol couplings. An unprecedented tandem transannular N-alkylation and removal of a Boc group was discovered to realize a biosynthesis-inspired process to furnish the desired tetracyclic skeleton. Of particular note is the unique and crucial tautomer locking strategy employed to complete the enantioselective total synthesis of (-)-lycojapodine A (6). The central step in this synthesis is the late-stage hypervalent iodine oxidant (IBX or Dess-Martin periodinane)/TFA-mediated tandem process, which constructed the previously unknown carbinolamine lactone motif and enabled a biomimetic transformation to generate (-)-lycojapodine A (6) in a single operation.

New alkaloids from Lycopodium japonicum

Three new alkaloids (1-3), together with ten known alkaloids, were isolated from the ethanolic extract of the whole plants of Lycopodium japonicum THUNB. Their structures were elucidated on the basis of spectroscopic analysis, including MS and NMR methods. All alkaloids isolated were assayed for cytotoxic activity against four human cancer cell lines and acetylcholinesterase (AChE) inhibitory activity. No alkaloid showed either cytotoxic activity against four human cancer cell lines or AChE inhibitory activity.

Synthesis of (±)-7-hydroxylycopodine

A seven-step synthesis of (±)-7-hydroxylycopodine that proceeds in 5% overall yield has been achieved. The key step is a Prins reaction in 60% sulfuric acid that gave the key tricyclic intermediate with complete control of the ring fusion stereochemistry. A one-pot procedure orthogonally protected the primary alcohol as an acetate and the tertiary alcohol as a methylthiomethyl ether. The resulting product was converted to 7-hydroxydehydrolycopodine by heating with KO-t-Bu and benzophenone in benzene followed by acidic workup. During unsuccessful attempts to make optically pure starting material, we observed the selective Pt-catalyzed hydrogenation of the 5-phenyl group of a 4,5-diphenyloxazolidine under acidic conditions and the Pt-catalyzed isomerization of the oxazolidine to an amide under neutral conditions. In attempts to hydroxylate the starting material so that we could adapt this synthesis to the preparation of (±)-7,8-dihydroxylycopodine (sauroine) we observed the novel oxidation of a bicyclic vinylogous amide to a keto pyridine with Mn(OAc)(3) and to an amino phenol with KHMDS and oxygen.

Regioselective hydroformylation of allylic alcohols

A highly regioselective hydroformylation of allylic alcohols is reported toward the synthesis of β-hydroxy-acid and aldehyde products. The selectivity is achieved through the use of a ligand that reversibly binds to alcohols in situ, allowing for a directed hydroformylation to occur. The application to trisubstituted olefins was also demonstrated, which yields a single diastereomer product consistent with a stereospecific addition of CO and hydrogen.

Removable directing groups in organic synthesis and catalysis

Directing groups have been widely used in recent years to achieve control over all aspects of reaction selectivity in a wide range of transformations involving transition-metal catalysis and organometallic reagents. In cases when the existing functional group within a substrate is unsuited to achieve efficient intramolecular delivery of a reagent or catalyst, the specific introduction of an appropriately designed removable reagent-directing group can be a solution to this problem. In this Review we give an overview of the state of the art in this area, including the stoichiometric and catalytic use of directing groups.

Synthesis of (±)-7-hydroxylycopodine

A six step synthesis of (±)-7-hydroxylycopodine has been achieved in 5% overall yield. In the key step, a Prins cyclization of a bicyclic keto alkyne in 60% H(2)SO(4) forms a tricyclic dihydroxy amino ketone.