Yuehchukene analogs

Relevant Developments in the Use of Three-Component Reactions for the Total Synthesis of Natural Products. The last 15 Years

Multicomponent reactions (MCRs) offer a highly useful and valuable strategy that can fulfill an important role in synthesizing complex polysubstituted compounds, by simplifying otherwise long sequences and increasing their efficiency. The total synthesis of selected natural products employing three-component reactions as their common strategic MCR approach, is reviewed on a case-by-case basis with selected targets conquered during the last 15 years. The revision includes detailed descriptions of the selected successful sequences; relevant information on the isolation, and bioactivity of the different natural targets is also briefly provided.

Benzoyl indoles with metabolic stability as reversal agents for ABCG2-mediated multidrug resistance

Ko143, a potent ABCG2 inhibitor that reverses multidrug resistance in cancer, cannot be used clinically due to its unsuitable metabolic stability. We identified benzoyl indoles as reversal agents that reversed ABCG2-mediated multidrug resistance (MDR), with synthetic tractability and enhanced metabolic stability compared to Ko143. Bisbenzoyl indole 2 and monobenzoyl indole 8 significantly increased the accumulation of mitoxantrone (MX) in ABCG2-overexpressing NCI-H460/MX20 cells, and sensitized NCI-H460/MX20 cells to mitoxantrone. Mechanistic studies were conducted by [³H]-MX accumulation assay, Western blot analysis, immunofluorescence analysis and ABCG2 ATPase assay. The results revealed that the reversal efficacies of compounds 2 and 8 were not due to an alteration in the expression level or localization of ABCG2 in ABCG2-overexpressing cell lines. Instead, compounds 2 and 8 significantly stimulated the ATP hydrolysis of ABCG2 transporter, suggesting that these compounds could be competitive substrates of ABCG2 transporter. Overall, the results of our study indicated that compounds 2 and 8 significantly reversed ABCG2-mediated MDR by blocking the efflux of anticancer drugs.

Biomimetically Inspired Synthesis of Exotine A

Exotine A, which comprises an unusual coumarin-cyclohepta[ b]indole ring system, has been synthesized for the first time in a one-pot process from known starting materials. The key step features a biomimetically inspired combination of three components to deliver exotine A and 11'- epi-exotine A in 43% yield and 17:1 diastereomeric ratio. Some mechanistic aspects of this reaction are discussed.

Total Synthesis of (±)-Exotine B

The heterodimeric indole/coumarin natural product exotine B was synthesized for the first time. The carbon skeleton of the natural product was formed rapidly by a palladium-catalyzed Suzuki cross-coupling reaction and a gallium-catalyzed three-component [4 + 3] cycloaddition reaction. An alternative biosynthesis of exotine B is proposed based on the total synthesis. Improved syntheses of coumarin natural products gleinadiene and coumurrayin are also reported.

Cu-Catalyzed selective C3-formylation of imidazo[1,2-a]pyridine C–H bonds with DMSO using molecular oxygen

Using the widely available DMSO as the formylation reagent under oxidative conditions, an efficient Cu-catalyzed C3-formylation reaction of imidazo [1,2-a]pyridine C–H bonds to directly generate structurally sophisticated 3-formyl imidazo[1,2-a]pyridine derivatives has been developed.

Novel Indole-N-glucoside, TA-1887 As a Sodium Glucose Cotransporter 2 Inhibitor for Treatment of Type 2 Diabetes

Inhibition of the renal sodium glucose cotransporter (SGLT) increases urinary glucose excretion (UGE) and thus reduces blood glucose levels during hyperglycemia. To explore the potential of new antihyperglycemic agents, we synthesized and determined the human SGLT2 (hSGLT2) inhibitory potential of novel substituted 3-benzylindole-N-glucosides 6. Optimization of 6 resulted in the discovery of 3-(4-cyclopropylbenzyl)-4-fluoroindole-N-glucoside 6a-4 (TA-1887), a highly potent and selective hSGLT2 inhibitor, with pronounced antihyperglycemic effects in high-fat diet-fed KK (HF-KK) mice. Our results suggest the potential of indole-N-glucosides as novel antihyperglycemic agents through inhibition of renal SGLT2.

Palladium-copper-cocatalyzed intramolecular oxidative coupling: an efficient and atom-economical strategy for the synthesis of 3-acylindoles

A new and efficient catalytic approach to the synthesis of 3-acylindoles under Pd-Cu-cocatalyzed oxidative conditions is demonstrated. tert-Butyl hydroperoxide (TBHP) acts not only as the oxidant, but also as an oxygen source in the approach. The process allows quick and atom-economical assembly of 3-acylindoles from readily available starting materials and tolerates a broad range of functional groups.

Mild and selective Ru-catalyzed formylation and Fe-catalyzed acylation of free (N-H) indoles using anilines as the carbonyl source

C3-selective formylation and acylation of free (N-H) indoles under mild conditions can be achieved by using Ru- and Fe-catalyzed oxidative coupling of free (N-H) indoles with anilines, respectively. Both processes are operationally simple, compatible with a variety of functional groups and generally provide the desired products in good yields. (13)C-labeling experiments unambiguously established that the carbonylic carbon in the formylation products originated from methyl group of N-methyl aniline.

Acid-Catalyzed Reactions of 3-Substituted-4,6-dimethoxyindoles with Ketones

Activated 3-substituted-4,6-dimethoxyindoles undergo acid catalyzed condensation with acetone and acetophenones in the presence of hydrochloric acid to give pyrrolo[a]indoles. Mixed pyrrolo[a]indoles can similarly be formed using a 1:1 mixture of two indoles. The reaction was found to be sensitive to acidity, with a 3:2 spiro condensation product being preferentially formed in the presence of p-toluenesulfonic acid.

Domino Carbocationic Rearrangement of α-[Bis(methylthio)methylene]alkyl-2-(3/2-indolyl) Cyclopropyl Ketones

Domino carbocationic rearrangement of a number of substituted 3- and 2-indolylcyclopropyl ketones with an alpha-bis(methylthio)methylene group in the presence of various protic/Lewis acids yields a variety of products, mainly the pentaleno fused indoles and the carbazole derivatives.