Photoelectrocyclization Reactions of Amidonaphthoquinones

The Role of N-Substitution in Regio- and Stereoselective Vinylogous Imidonaphthoquinone (VINAquinone) [2 + 2] Photocycloadditions

Described in this manuscript are intramolecular [2 + 2] photocycloadditions of readily available vinylogous imidonaphthoquinones whose regio- and diastereoselectivity is dependent on the substitution on the vinylogous imide. When exposed to 419 nm light, 2° vinylogous imidonaphthoquinones give novel bridged tetracyclic aza-anthraquinones from a rare crossed [2 + 2] cycloaddition reaction. In contrast, exposure of the corresponding 3° substrates to white light leads to linear adducts. Also outlined here are auxiliary controlled diastereoselective reactions and cyclobutane fragmentations as a means of generating the spirofused γ-lactam moiety present in the ansalactam family of natural product.

Heterocyclic Iminoquinones and Quinones from the National Cancer Institute (NCI, USA) COMPARE Analysis

This review uses the National Cancer Institute (NCI) COMPARE program to establish an extensive list of heterocyclic iminoquinones and quinones with similarities in differential growth inhibition patterns across the 60-cell line panel of the NCI Developmental Therapeutics Program (DTP). Many natural products and synthetic analogues are revealed as potential NAD(P)H:quinone oxidoreductase 1 (NQO1) substrates, through correlations to dipyridoimidazo[5,4-f]benzimidazoleiminoquinone (DPIQ), and as potential thioredoxin reductase (TrxR) inhibitors, through correlations to benzo[1,2,4]triazin-7-ones and pleurotin. The strong correlation to NQO1 infers the enzyme has a major influence on the amount of the active compound with benzo[e]perimidines, phenoxazinones, benz[f]pyrido[1,2-a]indole-6,11-quinones, seriniquinones, kalasinamide, indolequinones, and furano[2,3-b]naphthoquinones, hypothesised as prodrugs. Compounds with very strong correlations to known TrxR inhibitors had inverse correlations to the expression of both reductase enzymes, NQO1 and TrxR, including naphtho[2,3-b][1,4]oxazepane-6,11-diones, benzo[a]carbazole-1,4-diones, pyranonaphthoquinones (including kalafungin, nanaomycin A, and analogues of griseusin A), and discorhabdin C. Quinoline-5,8-dione scaffolds based on streptonigrin and lavendamycin can correlate to either reductase. Inhibitors of TrxR are not necessarily (imino)quinones, e.g., parthenolides, while oxidising moieties are essential for correlations to NQO1, as with the mitosenes. Herein, an overview of synthetic methods and biological activity of each family of heterocyclic imino(quinone) is provided.

Microwave-Assisted Three-Component Synthesis of Novel N-Arylated-Dihydrobenzo[g]quinoline-5,10-Diones and Their Potential Cytotoxic Activity

A convenient three-component synthetic approach was developed en route to new and significative N-arylated-dihydrobenzo[g]quinoline-5,10-diones using 2-hydroxy-1,4-naphthoquinone, a variety of aromatic aldehydes, and 4-(arylamino)furan-2(5H)-ones. A sequence of steps including Knoevenagel condensation, Michael addition, [1,3]-hydrogen shift, intramolecular cyclization and dehydration led to the formation of products. All the products were structurally characterized by spectroscopic techniques and assessed in terms of their cytotoxicity profile against four cancer cell lines (KB, HepG2, A549, and MCF7), and human embryonic kidney (Hek-293) cell lines.

Recent total syntheses of anthraquinone-based natural products

The scientific community has found deep interest in anthraquinone-based compounds due to their therapeutic properties and challenging structural elements. Various architecturally beautiful natural products have been successfully synthesized in recent decades utilizing two main strategies: either an early-stage synthesis of the anthraquinone and further elongation of the system, or a late-stage introduction of the anthraquinone ring moiety. Select syntheses of complex anthraquinone monomers and dimers within the past 20 years are described with an emphasis on the retrosynthetic disconnections that shape the anthraquinone-installation strategy.

Construction of 2-pyridones via oxidative cyclization of enamides: access to Pechmann dye derivatives

An efficient protocol for the construction of structurally diverse 2-pyridone derivatives from imines and α,β-unsaturated acid chlorides in a single operation is reported. The target compounds, including coumarin-8-oxoprotoberbine analogues and lamellarin G isomers, were prepared via thermal cyclization of the in situ generated enamides followed by thermal dehydrogenation. The cyclization of enamides was achieved by the introduction of an electron-withdrawing group on the α-carbon of acid chlorides. This methodology allows quick access to polycyclic Pechmann dyes via rare double oxidative cyclizations of dienamides under mild conditions.

Photocyclization of coumarinoyl enamides revisited: [2+2+2] cycloreversion/cycloaddition mechanism

The major and minor products for the photocyclization of coumarinoyl enamides were identified.

Tunable photochemical 6π heterocyclization reactions mediated by a boron Lewis acid

The regulation effect of boron Lewis acid catalyst on the photoinduced 6π heterocyclization was investigated by using multi-configurational ab initio calculations.

The one-pot synthesis of amidonapthoquinones from aminonaphthoquinones

Described here is a one-pot method of synthesizing amidonaphthoquinones from the corresponding aminonaphthoquinones. The scope of amides that can be synthesized using this methodology is relatively broad and the yield of product is higher than the traditional methods of synthesizing these substrates.