Phosphonium Ion-Tethered Secondary Amines for Chemospecific 5-Enolexo Aldol Condensations of 6-Ketoaldehydes

A novel and highly selective 5-enolexo-exo-trig aldol condensation of 6-ketoaldehydes is presented using a proline-based alkylphosphonium ion catalyst. Bulky and oxophilic phosphonium ion plays a vital role in facilitating kinetic aldenamine formation and activating keto groups for aldol addition. This innovative approach exclusively targets five-membered carbo- and heterocyclic aldehydes, involving unusual aldehydes as donors and ketones as acceptors. Especially, enolizable aryl keto aldehydes and heteroatom-embedded ketoaldehydes exclusively produced cyclized products with our new catalyst, while other catalysts provided predominantly self-aldol or decomposed products. The scope and diversity of the method demonstrated by synthesizing different carboxaldehydes, including cyclopentene, indene, dihydrofuran, benzofuran, dihydropyrrole, indole, thiofuran, dihydrothiofuran, and benzothiofurans.

Directing the Stereoselectivity of the Claisen Rearrangement to Form Cyclic Ketones with Full Substitution at the α-Positions

We report an enantioselective synthesis of cyclic ketones with full substitutions at the α-positions in a highly diastereoselective manner. Our method is achieved by subjecting substrate motifs in 2-allyloxyenones to chiral organomagnesium reagents, which trigger the Claisen rearrangement upon direct 1,2-carbonyl addition. The observed diastereoselectivity of the allyl migration is proposed to originate from the intramolecular chelation of the magnesium alkoxide to the allyloxy moiety.

Organocatalyzed enantio- and diastereoselective isomerization of prochiral 1,3-cyclohexanediones into nonalactones bearing distant stereocenters

The lactonization of 2-(2-nitrophenyl)-1,3-cyclohexanediones containing an alcohol side chain and up to three distant prochiral elements is reported by isomerization under the mediation of simple organocatalysts such as quinidine. Through a process of ring expansion, strained nonalactones and decalactone are produced with up to three stereocenters in high er and dr (up to 99 : 1). Distant groups, including alkyl, aryl, carboxylate and carboxamide moieties, were examined.

Exploration of Potent Cytotoxic Molecules from Fungi in Recent Past to Discover Plausible Anticancer Scaffolds

Fungi are known to produce diverse scaffolds possessing unique biological activities, however, to date, no molecule discovered from a fungal source has reached the market as an anti-cancer drug. Every year number of cytotoxic molecules of fungal origin are getting published and critical analysis of those compounds is necessary to identify the potent ones. A review mentioning the best cytotoxic fungal metabolites and their status in the drug development was published in 2014. In this report, we have included 176 cytotoxic molecules isolated from fungi after 2014 and categorized them according to their potencies such as IC₅₀ values below 1 μM, 1-5 μM, and 5-10 μM. The emphasis was given to those 42 molecules which have shown IC₅₀ less than 1 μM and discussed to a great extent. This review shall provide potent scaffolds of fungal origin which can be given priority in the development as a drug candidate for cancer therapeutics.

Marine natural products

Covering: 2020This review covers the literature published in 2020 for marine natural products (MNPs), with 757 citations (747 for the period January to December 2020) 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 (1407 in 420 papers for 2020), together with the relevant biological activities, source organisms and country of origin. Pertinent reviews, biosynthetic studies, first syntheses, and syntheses that led to the revision of structures or stereochemistries, have been included. A meta analysis of bioactivity data relating to new MNPs reported over the last five years is also presented.

Chemoinformatic Exploration of "Bioinspired Metabolomes" Illuminates Diacetyl Assembly Pathways Toward Nesteretal A-Like Cage Molecules

An appealing and challenging cage structure along with an unusual biosynthetic pathway prompted us to explore an expeditious bioinspired one-pot total synthesis of nesteretal A. An unconventional strategy was chosen, and a cascade reaction starting from diacetyl was studied. Under organocatalytic conditions mimicking an aldolase, nesteretal A and a related cage analogue were anticipated by in silico metabolization, detected, targeted, and characterized.

One-pot method for the synthesis of β-cyclodextrin and covalent organic framework functionalized chiral stationary phase with mixed-mode retention mechanism

As a welcomed porous material, covalent organic frameworks (COFs) have many advantages and are widely used in various aspects. Particularly, COFs have aroused great attentions of scientists in chromatographic separation field due to their outstanding advantages, such as high stability, large specific surface area and multiple voids. However, endowing COFs with chirality to construct chiral stationary phase (CSP) function is still facing many challenges. Here, we firstly prepared a β-cyclodextrin (β-CD) and covalent organic framework functional silica CSP named as COF@CD@SiO₂ by one-pot method to perform high performance liquid chromatography (HPLC) chiral separation. The morphology and structure of the synthesized stationary phase were investigated by a variety of characterization methods including Fourier transform infrared spectrometry (FT-IR), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), N₂ adsorption experiment, powder X-ray diffraction (XRD) and elemental analysis (EA). The prepared stationary phase realized fast separation of six enantiomers in a short time. The separation mechanism was mainly ascribed to the inclusion complexation of β-cyclodextrin and the mutli-interaction sites from COFs material. In conclusion, the prepared chiral column can be used to achieve fast separation of enantiomers with good stability and reproducibility. These results can open new avenue for using chiral COFs in liquid chromatographic separation.