Enantioselective Total Synthesis of (+)-Alstilobanine C, (+)-Undulifoline, and (-)-Alpneumine H

Recent strategy for the synthesis of indole and indoline skeletons in natural products

Indole alkaloids are one of the most important classes of natural products found in nature, particularly in a wide variety of plants. These compounds have compact polycyclic systems with at least one nitrogen atom. Several of these alkaloids are bioactive and have raised hopes for the development of new drugs. Their biosynthesis involves tryptophan as an amino acid precursor, since the indole or indoline moiety is the main heterocycle of these natural products. However, in their quest to synthesize such complex architectures, chemists have developed several different strategies to produce this key heterocycle quickly and in an unnatural way. This review focuses on the recent total synthesis methods used to prepare the indole and indoline core of these important alkaloids. Novel and older methods that allow the rapid formation of this heterocycle are described as key steps in the total synthesis of these fascinating structures designed by Mother Nature.

Divergent Enantioselective Total Synthesis of (-)-Ajmalicine, (+)-Mayumbine, and (-)-Roxburghine C

We report herein a divergent enantioselective total synthesis of (-)-ajmalicine, (+)-mayumbine, and (-)-roxburghine C. The synthesis employs Franzén's organocatalytic reaction between N-acetoacetyl tryptamine and (E)-5-hydroxypent-2-enal to generate a functionalized pentacyclic compound with high diastereo- and enantioselectivity. This intermediate serves as a versatile platform for accessing the three heteroyohimbine alkaloids. Notably, a diastereoselective intramolecular Pictet-Spengler reaction of methyl ketone and chemoselective reduction of β-amidoester to β-enaminoester were exploited for the synthesis of (-)-roxburghine C.

Constructing a highly sensitive duplex immunoassay using AuNPs and AgNPs as nanolabels for investigating the epithelial-mesenchymal transition occurring on circulating tumor cells with lung cancer patients

Transformation of epithelial to mesenchymal (EMT) is an important event in the process of tumor initiation, invasion and metastasis. Circulating tumor cells (CTCs) are one kind of important markers in the field of liquid tumor biopsy, whose number and phenotype represent the occurrence and progression of tumors. Therefore, it is our interest to investigate the epithelial mesenchymal transition process occurring on the surface of CTCs. Herein in this work, two proteins of E-cadherin (E-cad) and N-cadherin (N-cad) were selected as representative proteins of EMT process. To achieve simultaneous analysis of E-cad and N-cad on the surface of rare CTCs, we designed a duplex and portable immunosensor using AuNPs and AgNPs as nanolabels to amplify the immunoreaction signals. The dual channel immunosensor not only exhibited good electrochemical responses for recombinant E-cad and N-cad as low as 0.1 ng/mL and 0.05 ng/mL, respectively, but also showed good linear correlations with different numbers of phenotypic CTCs (10-500 cells/10 μL). The above strategy was further employed to inspect the occurrence of EMT on CTCs surface, which displayed a high consistence with other molecular biological characterizations. Finally, this immunoassay was successfully applied to inspect the correlations of numbers, phenotype of CTCs, as well as E-cad and N-cad expressions on these CTCs in bloods of NSCLC patients with disease stage.

Total Syntheses of Hosieines A-C

The collective total syntheses of (±)-hosieines A-C with a cage-like tetracyclic framework have been realized, which includes the first syntheses of hosieines B-C. The key strategy of the synthesis employs a one-pot domino reaction that involves Cu-catalyzed [3+2] cycloaddition, 1,6-enone formation, and 1,6-aza-Michael addition forming the 5/6/6-aza-tricyclic skeleton. Other salient synthetic tactics comprise a challenging double bond migration and a 1,4-aza-Michael addition reaction to afford the tetracyclic framework.

Alstoboonine, an Ulean-Type Indole Alkaloid from Alstonia boonei Leaves

Alstonia boonei De Wild is a common plant in West Africa used in traditional medicine for various indications. While the stem bark has frequently been investigated, not much is known about the phytochemistry and bioactivity of the leaves. Within the current study, the major alkaloids of a hydroethanolic leaf extract were therefore isolated and characterized by MS, NMR, and ECD. This led to the identification of alstoboonine 1, a new ulean-type alkaloid, along with eight previously reported indole alkaloids, 15-hydroxyangustilobine A (2), 6,7-seco-angustilobine B (3), 6,7-seco-19,20-α-epoxyangustilobine B (4), alstrostine E (5), alstrostine C (6), alstrostine D (7), 12-methoxyechitamidine (8), and 19-oxo-12-methoxyechitamidine (9). 1 was moderately active in vitro against Plasmodium falciparum NF54 (IC50 6.9 μM), but inactive against other protozoan parasites (Trypanosoma brucei, Trypanosoma cruzi, Leishmania donovani). No significant cytotoxic effects were observed in L6 rat skeletal myoblast cells and MCF-7 breast cancer cells. Similarly, compounds 3 to 9 did not show cytotoxicity in MCF-7 cells. Due to the reported traditional use of the plant as an anthelmintic, the major alkaloids 2, 5, 6, and 8 were tested against the nematode Caenorhabditis elegans. Nematicidal effects were observed for 6 (LC50 400 μM), whereas 2, 5, and 8 were inactive.