Efficient Synthetic Routes to (±)-Hippolachnin A, (±)-Gracilioethers E and F and the Alleged Structure of (±)-Gracilioether I

Unified Biomimetic Approach to (+)-Hippolachnin A: In-Depth Insights into Its Biosynthetic Origin

A formal biomimetic synthesis of (+)-hippolachnin A has been achieved under the guidance of its plausible biosynthetic pathway. Pivotal transformations include an intriguing 1O2-mediated [4 + 2] cycloaddition and a tandem Kornblum-DeLaMare rearrangement/hemiketalization/dehydration reaction. The current work not only offers a unified approach to access skeletally diverse plakortin-type polyketides but also provides convincing evidence to elucidate their underlying biosynthetic network.

Rh-Catalyzed cyclization of 2,3-allenoic acids in the presence of 2,3-allenols

Herein we report a [Cp*RhCl₂]₂-catalyzed coupling cyclization of two different classes of allenes with 2,3-allenoic acids affording 2(5H)-furanone skeletons of products and 2,3-allenols forming a conjugated (E)-enal or enone functionality to the β-position of the 2(5H)-furanones. These products are important building blocks for the syntheses of potentially bioactive compounds. The reaction proceeded via the nucleometalation, insertion, and stereodefined 1,4-H delivery carried by rhodium.

Biomimetic Synthesis of Natural Products: A Journey To Learn, To Mimic, and To Be Better

Total synthesis of natural products has been one of the most exciting and dynamic areas in synthetic organic chemistry. Nowadays, the major challenge in this field is not whether a given target of interest can be synthesized but how to make it with commendable efficiency and practicality. To meet this grand challenge, a wise way is to learn from Mother Nature who is recognized for her superb capability of forging complicated and sometimes beyond-imagination molecules in her own delicate way. Indeed, since Sir Robert Robinson published his groundbreaking synthesis of tropinone in 1917, biomimetic synthesis of natural products, a process of imitating nature's way to make molecules, has evolved into one of the most popular research directions in organic synthesis.Our group has been engaging in biomimetic synthesis of natural products in the past decade. During this time, we have come to realize that the successful implementation of a biomimetic synthesis entails the orchestrated combination of bioinspiration and rational design. On the one hand, we prefer to utilize some elegant bioinspired transformations (e.g., Diels-Alder dimerization, 6π-electrocyclization, and [2 + 2]-photocycloaddition) as the key steps of our synthesis, which enable rapid construction of the core skeletons of the chased targets with high efficiency; on the other hand, various powerful reactions (e.g., dyotropic rearrangement of β-lactone, tandem aldol condensation/Grob fragmentation reaction, and organocatalytic asymmetric Mukaiyama-Michael addition) are rationally designed by us, which allow for facile access to the requisite precursors for attempting biomimetic transformations. In some cases, the proposed biomimetic transformation may fail to give a satisfactory result in practice, and thus we opt to develop creative tactics (e.g., hydrogen atom transfer-triggered vinyl cyclobutane ring opening/oxygen insertion/cyclization cascade) that can meet the challenge. Guided by this synthesis concept, we have achieved the total syntheses of multiple families of natural products of great importance in both chemistry and biology, representatives of which include xanthanolides, cytochalasans, and plakortin-type polyketides. Of note, most of these targets could be accessed in a concise, efficient, and scalable manner, which paves the way for further exploration of their biological functions and medicinal potential. Moreover, owing to their biomimetic nature, our syntheses provide valuable information for deciphering the underlying biosynthetic pathways of the chased targets, which could not be attained by other synthetic modes.

Marine natural products from sponges (Porifera) of the order Dictyoceratida (2013 to 2019); a promising source for drug discovery

Marine organisms have been considered an interesting target for the discovery of different classes of secondary natural products with wide-ranging biological activities. Sponges which belong to the order Dictyoceratida are distinctly classified into 5 families: Dysideidae, Irciniidae, Spongiidae, Thorectidae, and Verticilliitidae. In this review, compounds isolated from Dictyoceratida sponges were discussed with their biological potential within the period 2013 to December 2019. Moreover, analysis of the physicochemical properties of these marine natural products was investigated and the results showed that 78% of the compounds have oral bioavailability potential. This review highlights sponges of the order Dictyoceratida as exciting source for discovery of new drug leads.

Marine organisms have been considered an interesting target for the discovery of different classes of secondary natural products with wide-ranging biological activities.

Recent advances in the synthesis of plakortin-type polyketides

Plakortin-type polyketides represent a growing family of sponge-derived marine natural products that display notable structural and biological diversity. In particular, a series of polycyclic plakortin polyketides, namely hippolachnin A and gracilioethers, have been identified in recent years, which attract immense interest from the synthetic community owing to their unique molecular architectures and promising biomedical potential. A number of elegant total syntheses of these targets and some synthetic studies have been performed through either bio-inspired or rationally designed strategies. This focused review aims to provide an up-to-date summary of the progress in the chemical synthesis of plakortin polyketides, with an emphasis on the key synthetic elements enabling the rapid assembly of their core skeletons.

Marine natural products

Covering: January to December 2017This review covers the literature published in 2017 for marine natural products (MNPs), with 740 citations (723 for the period January to December 2017) referring to compounds isolated from marine microorganisms and phytoplankton, green, brown and red algae, sponges, cnidarians, bryozoans, molluscs, tunicates, echinoderms, mangroves and other intertidal plants and microorganisms. The emphasis is on new compounds (1490 in 477 papers for 2017), together with the relevant biological activities, source organisms and country of origin. Reviews, biosynthetic studies, first syntheses, and syntheses that led to the revision of structures or stereochemistries, have been included. Geographic distributions of MNPs at a phylogenetic level are reported.

More than a CO source: palladium-catalyzed carbonylative synthesis of butenolides from propargyl alcohols and TFBen

Palladium-catalyzed direct carbonylation of propargyl alcohols for the synthesis of butenolides has been achieved.