Nodulisporic acid A synthetic studies. 2. Construction of an eastern hemisphere subtarget

Synthesis towards Phainanoid F: Photo-induced 6π-Electrocyclization for Constructing Contiguous All-Carbon Quaternary Centers

In this paper, we report an efficient strategy for synthesizing the DEFGH rings of phainanoid F. The key to the construction of the 13,30-cyclodammarane skeleton of the molecule was a photo-induced 6π-electrocyclization and a homoallylic elimination. Notably, this is a rare example of using electrocyclization reaction to simultaneously construct two vicinal quaternary carbons in total synthesis. The strategy outlined here forms the basis of our total synthesis of Phainanoid F, and it could also serve as a generally applicable approach for synthesizing other natural products containing similar 13,30-cyclodammarane skeletons.

Synthesis of rearranged indole diterpenes of the paxilline type

Covering: up to 2021Rearranged indole diterpenes of the paxilline type comprise a large group of fungal metabolites that possess diverse structural features and potentially useful biological effects. The unique indoloterpenoid motif, which is common to all congeners, was first confirmed by crystallographic studies of paxilline. This family of natural products has fascinated organic chemists for the past four decades and has inspired numerous syntheses and synthetic approaches. The present review highlights efforts that have laid the foundation and introduced new directions to this field of natural product synthesis. The introduction includes a summary of biosynthetic considerations and biological activities, the main body of the manuscript provides a detailed discussion of selected syntheses, and the review concludes with a brief outlook on the future of the field.

Total Synthesis of Shearinines D and G: A Convergent Approach to Indole Diterpenoids

The first total syntheses of the indole diterpenoids (+)‐shearinine G and D are disclosed. The successful routes rely on late‐stage coupling of two complex fragments. Formation of the challenging trans‐hydrindane motif was accomplished by diastereoselective, intramolecular cyclopropanation. A one‐pot sequence consisting of Sharpless dihydroxylation/Achmatowicz reaction was developed to install the dioxabicyclo[3.2.1]octane motif. The indenone subunit was accessed by Prins cyclization. Tuning the electronic nature of the substituents on the parent arylcarboxaldehyde allowed access to divergent products that were further transformed into shearinines G and D. Riley‐type oxidation of a bicyclic enone yielded a surprising stereochemical outcome.

Twelve-Step Asymmetric Synthesis of (-)-Nodulisporic Acid C

A short, enantioselective synthesis of (-)-nodulisporic acid C is described. The route features two highly diastereoselective polycyclizations en route to the terpenoid core and the indenopyran fragment and a highly convergent assembly of a challenging indole moiety. Application of this chemistry allows for a 12-step synthesis of the target indoloterpenoid from commercially available material.

Access to Wieland-Miescher Diketone-Derived Building Blocks by Stereoselective Construction of the C-9 Quaternary Carbon Center Using the Mukaiyama Aldol Reaction

The Mukaiyama aldol reaction has been used to efficiently install a lateral chain at the C-9 position of the Wieland-Miescher ketone derivative 3 within two steps, representing a shortcut compared to that of the classical sequences. The treatment of the silylated enol ether 8 with a wide range of acetals in the presence of tin tetrachloride led to a the diastereoselective construction of the C-9 quaternary center of 33 new building blocks derived from the Wieland-Miescher ketone derivative 3.

Total Synthesis of (-)-Nodulisporic Acid D

A convergent total synthesis of the architecturally complex indole diterpenoid (-)-nodulisporic acid D has been achieved. Key synthetic transformations include vicinal difunctionalization of an advanced α,β-unsaturated aldehyde to form the E,F-trans-fused 5,6-ring system of the eastern hemisphere and a cascade cross-coupling/indolization protocol leading to the CDE multisubstituted indole core.

Unusual cyclic terpenoids with terminal pendant prenyl moieties: from occurrence to synthesis

The paper reviews the known examples of cyclic terpenoids produced from open chain polyenic precursors by an "unusual" biosynthetic pathway, involving selective electrophilic attack on an internal double bond followed by cyclization. The resulting compounds possess cyclic backbones with pendant terminal prenyl groups. Synthetic approaches applied for the synthesis of such specifically functionalized compounds are also discussed, as well as biological activity of reported representatives.

Trifluoroacetic acid catalyzed thiophenylmethylation and thioalkylmethylation of lactams and phenols via domino three-component reaction in water

A new method for thiophenylmethylation and thioalkylmethylation of lactams and phenols has been described.

The Chemistry and Biology of Nakiterpiosin - C-nor-D-Homosteroids

Isolated from the sponge Terpios hoshinota that causes coral black disease, nakiterpiosin was the first C-nor-D-homosteroid discovered from a marine source. We provide in this account an overview of the chemistry and biology of this natural product. We also include a short history of the synthesis of C-nor-D-homosteroids and the results of some unpublished biological studies of nakiterpiosin.

Chemical and biological studies of nakiterpiosin and nakiterpiosinone

Nakiterpiosin and nakiterpiosinone are two related C-nor-D-homosteroids isolated from the sponge Terpios hoshinota that show promise as anticancer agents. We have previously described the asymmetric synthesis and revision of the relative configuration of nakiterpiosin. We now provide detailed information on the stereochemical analysis that supports our structure revision and the synthesis of the originally proposed and revised nakiterpiosin. In addition, we herein describe a refined approach for the synthesis of nakiterpiosin, the first synthesis of nakiterpiosinone, and preliminary mechanistic studies of nakiterpiosin's action in mammalian cells. Cells treated with nakiterpiosin exhibit compromised formation of the primary cilium, an organelle that functions as an assembly point for components of the Hedgehog signal transduction pathway. We provide evidence that the biological effects exhibited by nakiterpiosin are mechanistically distinct from those of well-established antimitotic agents such as taxol. Nakiterpiosin may be useful as an anticancer agent in those tumors resistant to existing antimitotic agents and those dependent on Hedgehog pathway responses for growth.

Palladium-catalyzed carbonylation reactions of aryl halides and related compounds

Palladium-catalyzed carbonylation reactions of aromatic halides in the presence of various nucleophiles have undergone rapid development since the pioneering work of Heck and co-workers in 1974, such that nowadays a plethora of palladium catalysts are available for different carbonylative transformations. The carboxylic acid derivatives, aldehydes, and ketones prepared in this way are important intermediates in the manufacture of dyes, pharmaceuticals, agrochemicals, and other industrial products. In this Review, the recent academic developments in this area and the first industrial processes are summarized.

Indole Diterpenoid Synthetic Studies. The Total Synthesis of (+)-Nodulisporic Acid F

[structure: see text] A stereocontrolled total synthesis of (+)-nodulisporic acid F, the simplest member of a family of novel ectoparasiticidal agents, has been achieved. Highlights of the effective modular synthetic strategy include anionic union of a tricyclic lactone with o-toluidine via our 2-substituted indole synthetic protocol, an optimized C-ring construction protocol, and a late-stage installation of the alpha,beta-unsaturated carboxylic acid side chain via the B-alkyl Suzuki-Miyaura cross-coupling tactic.

Nodulisporic acid side-chain modifications: access to the 2", 3", 4", and 6" registers

Efficient routes to access the 2", 3", 4", and 6" registers of the nodulisporic acid (NsA) side chain are disclosed. A mild one-carbon, Ph(2)CdoublebondNCH(2)CtriplebondN mediated homologation of NsA's 3"-aldehyde permitted access to the 4"-register. Curtius reaction of NsA's 3"-acid yielded the corresponding 2"-aldehyde 4 from which the unnatural Delta(2",3")-olefin isomer 2b was obtained. In addition, Arndt-Eistert reactions of the parent NsA permitted a one-carbon homologation to the 6" register. These efforts identified new analogues with significant flea activity and illustrated the biological significance of unsaturation at the 1",2" register.

Side-chain homologation of nodulisporic acid: synthesis of potent new dienyl derivatives

A series of new, diene-modified nodulisporic acid analogues (2) bearing diverse functionality at the 3"- and 4"-sites was efficiently prepared from the 3"-aldehyde 3. Biological evaluation of these synthetic nodulisporic acid analogues for systemic flea efficacy identified potent compounds and further clarified the structural requirements for ectoparasite activity.

Nodulisporic acid A synthetic studies. 1. Overall strategy and construction of a western hemisphere subtarget

In this, the first of two Letters, we outline our overall strategy for the construction of (+)-nodulisporic acid A (1), a representative member of a new class of indole diterpenes. In addition, we describe the efficient assembly of (-)-6, an advanced western hemisphere subtarget, comprising the ABC rings of (+)-nodulisporic acid A (1). The synthesis proceeded in 9% overall yield (longest linear sequence, 11 steps), exploiting a Shibasaki-Mori tandem transmetalation-cyclization to construct ring B. [reaction: see text]