Remote C-H Activation Strategy Enables Total Syntheses of Nortriterpenoids (±)-Walsucochin B and (±)-Walsucochinoids M and N

Titanium-Mediated Dehydroxylative Cross-Coupling of Allylic Alcohols with Electron-Deficient Olefins

Herein we report a Ti(III)-mediated dehydroxylative cross-coupling reaction of allylic alcohols with electron-deficient olefins. This reaction is amenable to various synthetically versatile allylic alcohols, including geraniol and farnesol, providing a general method for dehydroxylative C-C bond formation. We demonstrated the reaction's utility by simplifying the syntheses of eight useful building blocks that are otherwise laborious to prepare.

Marine Puupehenone and Puupehedione: Synthesis and Future Perspectives

Puupehenone and puupehedione are natural products isolated from marine organisms. These compounds display a broad spectrum of biological activities, the in vitro antitubercular activity of puupehenone being a stand out, and are equipped with an interesting structural complexity. These products have served to stimulate the continual interest of the synthetic community. The first part of this article is a review of their total synthesis, using natural compounds which have the potential to be transformed into these marine compounds as starting materials; the synthetic routes employed to generate the basic skeleton; and the advances made to synthesize the pyran C ring with the required diastereoselectivity to obtain the natural products. Finally, this perspective shows a personal reflection of the authors on a possible unified and efficient retrosynthetic route that could allow easy access to these natural products, as well as their epimers at the C8 carbon and which could be used to address future biological issues in the production of pharmacologically active compounds.

Asymmetric Total Synthesis of (+)-Phainanoid A and Biological Evaluation of the Natural Product and Its Synthetic Analogues

Here, we report our detailed efforts toward the synthesis of phainanoids, a novel class of dammarane-type triterpenoids with potent immunosuppressive activities and unique structural features. Systematic model studies have been carried out, and efficient approaches have been established to construct the benzofuranone-based 4,5-spirocycle, the D/E/F tricyclic core, the [4.3.1] propellane, and the 5,5-oxaspirolactone moieties. The asymmetric synthesis of (+)-phainanoid A has been achieved through kinetic resolution of the tricyclic core followed by diastereoselective installation of the A/B/C and G/H rings and fragment coupling with the enantioenriched I/J rings. In addition, novel estrone-derived phainanoid analogues have been prepared. The immunosuppressive and cell survival assays revealed that (+)-phainanoid A and some of its synthetic analogues can specifically inhibit stimulation-induced lymphocyte proliferation but not cell survival at their effective concentrations. Preliminary structure-activity relationship information has been obtained, which could inspire future design of immunosuppressive phainanoid analogues.

Construction of the Skeleton of Lucidumone

The skeleton of lucidumone was constructed through oxidative dearomatization/intramolecular Diels-Alder reaction, Cu-mediated remote C-H hydroxylation, allyl oxidation, acid-promoted dynamic kinetic resolution cyclization, and benzylic oxidation.

Research progress of meliaceous limonoids from 2011 to 2021

Covering: July 2010 to December 2021Limonoids, a kind of natural tetranortriterpenoids with diverse skeletons and valuable insecticidal and medicinal bioactivities, are the characteristic metabolites of most plants of the Meliaceae family. The chemistry and bioactivities of meliaceous limonoids are a continuing hot area of natural products research; to date, about 2700 meliaceous limonoids have been identified. In particular, more than 1600, including thirty kinds of novel rearranged skeletons, have been isolated and identified in the past decade due to their wide distribution and abundant content in Meliaceae plants and active biosynthetic pathways. In addition to the discovery of new structures, many positive medicinal bioactivities of meliaceous limonoids have been investigated, and extensive achievements regarding the chemical and biological synthesis have been made. This review summarizes the recent research progress in the discovery of new structures, medicinal and agricultural bioactivities, and chem/biosynthesis of limonoids from the plants of the Meliaceae family during the past decade, with an emphasis on the discovery of limonoids with novel skeletons, the medicinal bioactivities and mechanisms, and chemical synthesis. The structures, origins, and bioactivities of other new limonoids were provided as ESI. Studies published from July 2010 to December 2021 are reviewed, and 482 references are cited.

The Genus Walsura: A Rich Resource of Bioactive Limonoids, Triterpenoids, and Other Types of Compounds

Medicinal plants of the genus Walsura (family Meliaceae) are native to tropical zones of a number of Asian countries, and have been used in systems of folk medicine. Several original research articles on Walsura species are available, but an overview highlighting the phytochemical and biological aspects of the compounds isolated to date is so far absent. Since the 1970s, phytochemical investigations on the genus Walsura have been undertaken, and more than 220 compounds from ten species have been identified. Natural products from Walsura species that have received the most attention are limonoids (114 compounds) and triterpenoids (72 compounds). Walsura limonoids have been characterized structurally as having diverse skeletons and more than 100 such compounds are new to the literature, while dammaranes, tirucallanes, and apotirucallanes are the main triterpenoid types from this genus. Other Walsura constituents comprise sesquiterpenoids, flavonoids, sterols, lignans, xanthones, and anthraquinones. Walsura species constituents have also been studied in natural product drug discovery screening programs. Many in vitro biological and some in vivo pharmacological investigations have been carried out on Walsura species isolated compounds. Walsura components display properties such as cancer cell cytotoxicity, antimicrobial, antidiabetes, anti-inflammatory, antioxidant, antifeedant, antifertility, ichthyotoxic, and neuroprotection activities.

Bidirectional Total Synthesis of Phainanoid A via Strategic Use of Ketones

Here we report the total synthesis of phainanoid A, a unique dammarane-type triterpenoid (DTT), using an unusual bidirectional synthetic strategy. It features two transition-metal-mediated highly diastereoselective transformations to access the two challenging strained ring systems that branch toward opposite directions from the tricyclic core. This work also highlights the strategic use of ketones (or enol triflates) as versatile handles for rapid growth of molecular complexity in all key transformations, which paves the way for efficient preparations of complex and biologically significant DTTs.

Practical One-Pot Multistep Synthesis of 2H-1,3-Benzoxazines Using Copper, Hydrogen Peroxide and Triethylamine

In this article, we describe simple one-pot syntheses of 2H-1,3-benzoxazines from ketones utilizing an imino-pyridine directing group (R¹R²-C=N-CH₂-Pyr), which promotes a Cu-directed sp² hydroxylation using H₂O₂ as oxidant and followed by an oxidative intramolecular C-O bond formation upon addition of NEt₃. This synthetic protocol is utilized in the gram scale synthesis of the 2H-1,3-benzoxazine derived from benzophenone. Mechanistic studies reveal that the cyclization occurs via deprotonation of the benzylic position of the directing group to produce a 2-azallyl anion intermediate, which is oxidized to the corresponding 2-azaallyl radical before the C-O bond formation event. Understanding of the cyclization mechanism also allowed us to develop reaction conditions that utilize catalytic amounts of Cu.

Divergent Entry to Walsucochin Nortriterpenoids: Total Syntheses of (±)-Walsucochin A and (±)-Walsucochinoids C-F

Nortriterpenoids isolated from Walsura cochinchinensis have attracted much attention from both synthetic and medicinal chemists, yet only recently have efficient synthetic approaches to any members appeared. Shown here is that the common intermediate with a 6/6/5/6-fused tetracyclic ring nucleus can be converted to walsucochin family members. The first total syntheses of (±)-walsucochin A, (±)-walsucochinoids C-F, and their analogues were achieved in this work.