Enantioselective Synthesis of α-Alkylmalates as the Pharmacophoric Group of Several Natural Alkaloids and Glycosides

Arundinosides I-IX and graminifolosides A-B: 2R-benzylmalate and 2R-isobutylmalates derivatives from Arundina graminifolia (D.Don) Hochr. with antioxidant, cytocompatibility and cytoprotective properties

Phytochemical investigation of the underground parts of Arundina graminifolia D.Don Hochr was conducted leading to the isolation of nine new glucosyloxybenzyl 2R-benzylmalate and two new glucosyloxybenzyl 2R-isobutylmalate derivatives. The compounds were purified using chromatographic techniques and their structures were deduced based on spectroscopic techniques including nuclear magnetic resonance and high-resolution mass spectrometry as well as comparing with previous literature. The antioxidant activities of the isolated compounds were also evaluated. The compounds showed potent antioxidant activities in the ABTS radical scavenging, DPPH radical scavenging and FRAP activities. Furthermore, the isolated compounds were observed to exert minimal cytotoxic effects against RAW 264.7 cell, suggesting biocompatibility as well as cytoprotective effects against hydrogen peroxide induced cell toxicity.

Hepatoprotective activity of glucosyloxybenzyl succinate derivatives from the pseudobulbs of Pleione bulbocodioides

Ten previously undescribed glucosyloxybenzyl succinate derivatives, pleionosides A-J, and fifteen known compounds were isolated from the pseudobulbs of Pleione bulbocodioides (Franch.) Rolfe. Their structures were elucidated by a combination of MS and NMR data, physical and chemical methods and a comparison with known compounds. Furthermore, three compounds exhibited potent hepatoprotective activity against N-acetyl-p-aminophenol (APAP)-induced HepG2 cell damage in in vitro assays, with cell survival rates of 31.89%, 31.52% and 31.97% at 10 μM. Four compounds exhibited moderate antioxidant activity with increasing viability at 10 μM of 36.1%, 45.0%, 25.5% and 20.7%.

Catalytic enantioselective Hosomi–Sakurai reaction of α-ketoesters promoted by chiral copper(ii) complexes

The first catalytic enantioselective Hosomi−Sakurai reaction of α-ketoesters.

New Alkaloid and Aromatic Glucoside from the Flowers of Cymbidium Lunagrad Eternal Green

In this paper, we investigated the chemical components of the flowers of Cymbidium Lunagrad Eternal Green for the first time. In the whole post-fertilization, a new alkaloid, named Lunagrad A (1), and a new aromatic glucoside, named Lunagrad B (2), were isolated from the MeOH extract of the flowers of Cymbidium Lunagrad Eternal Green, along with other six known aromatic compounds (3–8) and three flavone glucosides (9–11). These structures were determined on the basis of NMR experiments, as well as chemical evidence.

Cephalotaxus Alkaloids

Cephalotaxus alkaloids represent a family of plant secondary metabolites known for 60 years. Significant activity against leukemia in mice was demonstrated for extracts of Cephalotaxus. Cephalotaxine (CET) (1), the major alkaloid of this series was isolated from Cephalotaxus drupacea species by Paudler in 1963. The subsequent discovery of promising antitumor activity among new Cephalotaxus derivatives reported by Chinese, Japanese, and American teams triggered extensive structure elucidation and biological studies in this family. The structural feature of this cephalotaxane family relies mainly on its tetracyclic alkaloid backbone, which comprises an azaspiranic 1-azaspiro[4.4]nonane unit (rings C and D) and a benzazepine ring system (rings A and B), which is linked by its C3 alcohol function to a chiral oxygenated side chain by a carboxylic function alpha to a tetrasubstituted carbon center. The botanical distribution of these alkaloids is limited to the Cephalotaxus genus (Cephalotaxaceae). The scope of biological activities of the Cephalotaxus alkaloids is mainly centered on the antileukemic activity of homoharringtonine (HHT) (2), which in particular demonstrated marked benefits in the treatment of orphan myeloid leukemia and was approved as soon as 2009 by European Medicine Agency and by US Food and Drug Administration in 2012. Its exact mechanism of action was partly elucidated and it was early recognized that HHT (2) inhibited protein synthesis at the level of the ribosome machinery. Interestingly, after a latency period of two decades, the topic of Cephalotaxus alkaloids reemerged as a prolific source of new natural structures. To date, more than 70 compounds have been identified and characterized. Synthetic studies also regained attention during the past two decades, and numerous methodologies were developed to access the first semisynthetic HHT (2) of high purity suitable for clinical studies, and then high grade enantiomerically pure CET (1), HHT (2), and analogs.

Diastereoselective Synthesis of Cephalotaxus Esters via Asymmetric Mukaiyama Aldol Reaction

We report a protocol for efficient stereoselective installation of the chiral oxygen-containing tetrasubstituted tertiary carbon stereocenter of the side chain of cephalotaxus esters by means of highly diastereoselective Mukaiyama aldol reactions between α-keto esters (2) and a (Z)-α-chloro ketene silyl acetal. This protocol permitted synthesis of cephalotaxus esters including six natural products in good to excellent yields (up to 94%) with high diastereoselectivities (dr up to 97:3) and could be performed on a multigram scale.

A Concise and Scalable Formal Synthesis of the Enantiopure Side-Chain Diester of Homoharringtonine

The enantiopure side-chain diester of homoharringtonine (HHT) has been prepared in 38% overall yield, from cheap L-aspartic acid by a linear sequence of 10 chemical operations (mean yield per step: 91%). The experimental operation in each step is convenient, economic and prone to scale up. About 7–10 g of the side-chain diester of HHT is easily prepared within one week from 5 g of L-aspartic acid.

Phenanthrenes, 9,10-dihydrophenanthrenes, bibenzyls with their derivatives, and malate or tartrate benzyl ester glucosides from tubers of Cremastra appendiculata

Eleven previously unknown compounds and 23 known compounds, including 20 phenanthrene or 9,10-dihydrophenanthrene derivatives, five bibenzyls, seven malate or tartrate benzyl ester glucosides, adenosine and gastrodin were isolated from tubers of Cremastra appendiculata. Among the obtained compounds, two are the first isolated dimers with one phenanthrene or bibenzyl unit connected to C-3 of 2,3,4,5-tetrahydro-phenanthro[2,1-b]furan moiety. In addition, 33 of these compounds were evaluated in vitro for their cytotoxic activity against two cancer cell lines. Among the compounds examined, one compound showed moderate cytotoxic activity, while five showed weak cytotoxic activity against the A549 cell line.

Enantiospecific synthesis of the diacid side-chain of deoxyharringtonine and homodeoxyharringtonine

The enantiospecific synthesis of the diacid side-chain of deoxyharringtonine (2) and homodeoxyharringtonine (3) was accomplished from (L)-N-Boc-α-amino alcohol 10 in high yield. A key feature of the synthesis is the construction of the chiral tertiary alcohol by a three-step sequence (i.e., Wittig reaction, Meisenheimer rearrangement, and catalytic hydrogenation).

Construction of chiral tertiary alcohol stereocenters via the [2,3]-Meisenheimer rearrangement: enantioselective synthesis of the side-chain acids of homoharringtonine and harringtonine

For the first time, the [2,3]-Meisenheimer rearrangement has been developed into a general strategy for the construction of chiral tertiary alcohols. The effectiveness and practicality of this methodology are illustrated by the successful synthesis of (R)-20 and (R)-30, the side chain acids of homoharringtonine and harringtonine, respectively.

Aromatic constituents of Cymbidium Great Flower Marie Laurencin and their antioxidative activity

Two novel aromatic glucosides, named marylaurecinosides B (1) and C (2), were isolated from Cymbidium Great Flower Marie Laurencin, together with six known aromatic compounds (3-8). These structures were determined on the basis of NMR experiments as well as chemical evidence. All of the isolated compounds (1-8) were tested for antioxidative activity using a superoxide dismutase-like assay.

Synthesis of antiproliferative Cephalotaxus esters and their evaluation against several human hematopoietic and solid tumor cell lines: uncovering differential susceptibilities to multidrug resistance

Deoxyharringtonine (2), homoharringtonine (3), homodeoxyharringtonine (4), and anhydroharringtonine (5) are reported to be among the most potent members of the antileukemia alkaloids isolated from the Cephalotaxus genus. Convergent syntheses of these four natural products are described, each involving novel synthetic methods and strategies. These syntheses enabled evaluation of several advanced natural and non-natural compounds against an array of human hematopoietic and solid tumor cells. Potent cytotoxicity was observed in several cell lines previously not challenged with these alkaloids. Variations in the structure of the ester chain within this family of alkaloids confer differing activity profiles against vincristine-resistant HL-60/RV+, signalling new avenues for molecular design of these natural products to combat multi-drug resistance.