Unnatural C-1 homologues of pancratistatin - Synthesis and promising biological activities

Total synthesis of 1,4a-di-epi-ent-pancratistatin, exemplifying a stereodivergent approach to pancratistatin isomers

The total synthesis of 1,4a-di-epi-ent-pancratistatin, a novel stereoisomer of the anti-tumor Amaryllidaceae alkaloid pancratistatin, was achieved in 14 steps starting from D-mannitol. The construction of the pancratistatin skeleton involved conjugate addition of organocuprate to a nitrosoolefin, which was generated in situ from inosose oxime. This was followed by stereoselective reduction of the oxime to an amine and site-selective formylation. Biological evaluations revealed that the newly synthesized compounds exhibit cytotoxicity toward cancer cells and significant ferroptosis inhibitory activity. These compounds constitute a promising small-molecule library for the development of potent bioactive agents.

Total Synthesis of (+)-Pancratistatin and Its Potent Topo I Inhibition Activity Studies

As a preeminent anticancer natural product, (+)-pancratistatin has always been a privileged synthetic target. Herein, the total synthesis of (+)-pancratistatin is reported in 10 linear steps by utilizing a known aldehyde as chiral source. This synthetic route features a highly stereoselective intermolecular Michael addition and intramolecular Henry reaction to construct a cyclohexane ring bearing 6 successive stereocenters. Moreover, all of the synthetic steps are reliable and efficient and can be easily scaled up, which facilitated anticancer pharmacological tests of (+)-pancratistatin. Importantly, a new pharmacological mechanism of action was discovered for the first time where (+)-pancratistatin is able to inhibit the activity of topoisomerase I, which would pave the way for the development of new-type Topo I inhibitors.

Conversion of Natural Narciclasine to Its C-1 and C-6 Derivatives and Their Antitumor Activity Evaluation: Some Unusual Chemistry of Narciclasine

During the search for a general, efficient route toward the synthesis of C-1 analogues of narciclasine, natural narciclasine was protected and converted to its C-1 enol derivative using a novel semi-synthetic route. Attempted conversion of this material to its triflate in order to conduct cross-coupling at C-1 resulted in a triflate at C-6 that was successfully coupled with several functionalities. Four novel compounds were fully deprotected after seven steps and subjected to evaluation for cytotoxic activity against three cancer cell lines. Only one derivative showed moderate activity compared to that of narciclasine. Spectral and physical data are provided for all new compounds.

Design and Synthesis of C-1 Methoxycarbonyl Derivative of Narciclasine and Its Biological Activity

A 15-step chemoenzymatic total synthesis of C-1 methoxycarbonyl narciclasine (10) was accomplished. The synthesis began with the toluene dioxygenase-mediated dihydroxylation of ortho-dibromobenzene to provide the corresponding cis-dihydrodiol (12) as a single enantiomer. Further key steps included a nitroso Diels-Alder reaction and an intramolecular Heck cyclization. The C-1 homolog 10 was tested and evaluated for antiproliferative activity against natural narciclasine (1) as the positive control. Experimental and spectral data are reported for all novel compounds.

(±)-trans-Dihydronarciclasine and (±)-trans-dihydrolycoricidine analogues modified in their ring A: Evaluation of their anticancer activity and a SAR study

A series of (±)-trans-dihydronarciclasine and (±)-trans-dihydrolycoricidine derivatives with variously substituted ring A was synthesised and evaluated for their antiproliferative activity against 60 human tumour cell lines (NCI60), representing leukemia, melanoma, and cancers of the lung, colon, brain, ovary, breast, prostate, as well as kidney in vitro. Among the 13 alkaloids screened, (±)-trans-dihydronarciclasine showed the highest potency as a cytotoxic molecule. A structure-activity relationship (SAR) study indicated that the presence of a hydroxy group at position 7 and a rigid, 1,3-benzodioxole scaffold were essential for the antiproliferative activity.

Benefits of Unconventional Methods in the Total Synthesis of Natural Products

This article provides a survey of four "unconventional" methods employed in the synthesis of natural products in the Hudlicky group. The utility of flash vacuum pyrolysis is highlighted by examples of many natural products attained via vinylcyclopropane-cyclopentene rearrangement and its heterocyclic variants. Preparative organic electrochemistry was used in oxidations and reductions with levels of selectivity unattainable by conventional methods. Yeast reduction of ketoesters was featured in the total synthesis of pyrrolizidine alkaloids. Finally, the use of toluene dioxygenase-mediated dihydroxylations in enantioselective synthesis of natural products concludes this presentation. Recently, synthesized targets in the period 2010-2019 are listed in the accompanying table. The results of research from the Hudlicky group are placed in appropriate context with the work of others, and a detailed guide to the current literature is provided.

Stereoselective synthesis of trans-dihydronarciclasine derivatives containing a 1,4-benzodioxane moiety

ABSTRACT

Some new trans-dihydronarciclasine derivatives containing a 1,4-benzodioxane moiety were stereoselectively synthesised using our feasible and efficient method developed recently. These new phenanthridone alkaloid analogues were obtained in both racemic and optically active forms. High enantioselectivities (up to 99% ee) were achieved by applying (8S,9S)-9-amino(9-deoxy)epiquinine as an organocatalyst. Due to a side reaction, various methoxyphenanthridine regioisomers were also prepared which afforded further synthetic trans-dihydronarciclasine analogues modified in the ring A of the phenanthridone scaffold.

GRAPHICAL ABSTRACT

Asymmetric Entry into 10b-aza-Analogues of Amaryllidaceae Alkaloids Reveals a Pronounced Electronic Effect on Antiviral Activity

Development of a chiral pool-based synthesis of 10b-aza-analogues of biologically active Amaryllidaceae alkaloids is described, involving a concise reductive amination and condensation sequence, leading to ring-B/C-modified, fully functionalized ring-C derivatives. Differentiated anticancer and antiviral activities of these analogues are presented. Despite complete conformational and functional group overlap, the 10b-aza-analogues have diminished anticancer activity and no antiviral activity. These unprecedented electronic effects suggest a possible role for π-type secondary orbital interactions with the biological target.

5,10b-Ethanophenanthridine amaryllidaceae alkaloids inspire the discovery of novel bicyclic ring systems with activity against drug resistant cancer cells

Plants of the Amaryllidaceae family produce a large variety of alkaloids and non-basic secondary metabolites, many of which are investigated for their promising anticancer activities. Of these, crinine-type alkaloids based on the 5,10b-ethanophenanthridine ring system were recently shown to be effective at inhibiting proliferation of cancer cells resistant to various pro-apoptotic stimuli and representing tumors with dismal prognoses refractory to current chemotherapy, such as glioma, melanoma, non-small-cell lung, esophageal, head and neck cancers, among others. Using this discovery as a starting point and taking advantage of a concise biomimetic route to the crinine skeleton, a collection of crinine analogues were synthetically prepared and evaluated against cancer cells. The compounds exhibited single-digit micromolar activities and retained this activity in a variety of drug-resistant cancer cell cultures. This investigation resulted in the discovery of new bicyclic ring systems with significant potential in the development of effective clinical cancer drugs capable of overcoming cancer chemotherapy resistance.

Synthesis and biological evaluation of unnatural derivatives of narciclasine: 7-aza-nornarciclasine and its N-oxide

Several unnatural derivatives of narciclasine were prepared in which the C-7 carbon was replaced with nitrogen. The 7-aza derivative and its N-oxide were prepared by the coupling of iodopicolinic acid with a conduramine unit derived chemoenzymatically from bromobenzene. Intramolecular Heck reaction was used to construct the isocarbostyryl ring system. The compounds were submitted to biological screening against cancer cell lines. Full experimental and spectra data are provided for all new compounds.

Reactions of enantiopure cyclic diols with sulfuryl chloride

Monocyclic allylic cis-1,2-diols reacted with sulfuryl chloride at 0 °C in a regio- and stereo-selective manner to give 2-chloro-1-sulfochloridates, which were hydrolysed to yield the corresponding trans-1,2-chlorohydrins. At -78 °C, with very slow addition of sulfuryl chloride, cyclic sulfates were formed in good yields, proved to be very reactive with nucleophiles and rapidly decomposed on attempted storage. Reaction of a cyclic sulfate with sodium azide yielded a trans-azidohydrin without evidence of allylic rearrangement occurring. An enantiopure bicyclic cis-1,2-diol reacted with sulfuryl chloride to give, exclusively, a trans-1,2-dichloride enantiomer with retention of configuration at the benzylic centre and inversion at the non-benzylic centre; a mechanism is presented to rationalise the observation.

The role of biocatalysis in the asymmetric synthesis of alkaloids

Alkaloids are not only one of the most intensively studied classes of natural products, their wide spectrum of pharmacological activities also makes them indispensable drug ingredients in both traditional and modern medicine. Among the methods for their production, biotechnological approaches are gaining importance, and biocatalysis has emerged as an essential tool in this context. A number of chemo-enzymatic strategies for alkaloid synthesis have been developed over the years, in which the biotransformations nowadays take an increasingly 'central' role. This review summarises different applications of biocatalysis in the asymmetric synthesis of alkaloids and discusses how recent developments and novel enzymes render innovative and efficient chemo-enzymatic production routes possible.

IMDAF/aromatization path of halogenated furylacrylamides and furylpropiolamides to dihydroisoquinolin-1(2H)-ones

Intramolecular Diels-Alder cycloadditions of chlorofuryl- (R = Cl) secondary (R' = H) acrylamides and propiolamides of type 1 followed by (optional modification and) base-induced aromatization of the resulting chlorinated oxanorborn(adi)enes 2 afford N-free-dihydroisoquinolin-1(2H)-ones 3 with different aromatic substitution patterns.