Stereocontrolled total synthesis of pancratistatin

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.

Short, enantioselective, gram-scale synthesis of (-)-zephyranthine

A reasonable synthesis design by strategically integrating functional group manipulation into the ring system construction resulted in a short, enantioselective, gram-scale total synthesis of (−)-zephyranthine. The concise route includes a catalytic Michael/Michael cascade for the asymmetric synthesis of a penta-substituted cyclohexane with three contiguous stereogenic centers, a remarkable 8-step one-pot operation to easily assemble the zephyranthine tetracyclic skeleton, the regioselective construction of a double bond in the C ring and an asymmetric dihydroxylation. This synthesis is also flexible and paves a potential path to a variety of cyclohexylamine-fused tricyclic or polycyclic alkaloids.

A reasonable synthesis design by strategically integrating functional group manipulation into the ring system construction resulted in a short, enantioselective, gram-scale total synthesis of (−)-zephyranthine.

Nitrone and Alkyne Cascade Reactions for Regio- and Diastereoselective 1-Pyrroline Synthesis

The synthesis of 1-pyrrolines from N-alkenylnitrones and alkynes has been explored as a retrosynthetic alternative to traditional approaches. These cascade reactions are formal [4+1] cycloadditions that proceed through a proposed dipolar cycloaddition and N-alkenylisoxazoline [3,3']-sigmatropic rearrangement. A variety of cyclic alkynes and terminal alkynes have been shown to undergo the transformation with N-alkenylnitrones under mild conditions to provide the corresponding spirocyclic and densely substituted 1-pyrrolines with high regio- and diastereoselectivity. Mechanistic studies provide insight into the balance of steric and electronic effects that promote the cascade process and control the diastereo- and regioisomeric preferences of the 1-pyrroline products. Diastereoselective derivatization of the 1-pyrrolines prepared by the cascade reaction demonstrate the divergent synthetic utility of the new method.

Enantioselective Synthesis of Isocarbostyril Alkaloids and Analogs Using Catalytic Dearomative Functionalization of Benzene

Enantioselective total syntheses of the anticancer isocarbostyril alkaloids (+)-7-deoxypancratistatin, (+)-pancratistatin, (+)-lycoricidine, and (+)-narciclasine are described. Our strategy for accessing this unique class of natural products is based on the development of a Ni-catalyzed dearomative trans-1,2-carboamination of benzene. The effectiveness of this dearomatization approach is notable, as only two additional olefin functionalizations are needed to construct the fully decorated aminocyclitol cores of these alkaloids. Installation of the lactam ring has been achieved through several pathways and a direct interconversion between natural products was established via a late-stage C-7 cupration. Using this synthetic blueprint, we were able to produce natural products on a gram scale and provide tailored analogs with improved activity, solubility, and metabolic stability.

Synthesis of (+)-Pancratistatins via Catalytic Desymmetrization of Benzene

A concise synthesis of (+)-pancratistatin and (+)-7-deoxypancratistatin from benzene using an enantioselective, dearomative carboamination strategy has been achieved. This approach, in combination with the judicious choice of subsequent olefin-type difunctionalization reactions, permits rapid and controlled access to a hexasubstituted core. Finally, minimal use of intermediary steps as well as direct, late stage C-7 hydroxylation provides both natural products in six and seven operations.

Total Synthesis of (+)-Pancratistatin by the Rh(III)-Catalyzed Addition of a Densely Functionalized Benzamide to a Sugar-Derived Nitroalkene

Herein, we report the concise total synthesis of (+)-pancratistatin, accessed in a 10-step linear sequence from commercially available inputs. The convergent synthesis features a highly diastereoselective Rh(III)-catalyzed C-H bond addition to a d-glucose-derived nitroalkene and a late-stage intramolecular transamidation to furnish the B ring lactam.

Enantioselective synthesis of protected nitrocyclohexitols with five stereocenters. Total synthesis of (+)-pancratistatin

2-Methoxymethylpyrrolidine best performed, among several other proline derivatives, to control the enantioselective [3+3] annulation of β-(hetero)aryl-α-nitro-α,β-enals with commercial 2,2-dimethyl-1,3-dioxan-5-one, a procedure that renders highly oxygenated nitrocyclohexanes endowed with five new stereocenters. Use of this reaction allowed the development of a total synthesis of the antitumoral natural product (+)-pancratistatin; it also converted our previous racemic route to tetrodotoxin into an enantioselective one.

Copper-catalyzed iminoiodane-mediated aminolactonization of olefins: application to the synthesis of 5,5-disubstituted butyrolactones

A copper(I)-catalyzed reaction of a variety of 4-aryl-pent-4-enoates with nosyliminoiodane generated in situ provides the corresponding 5-aryl-5-nosylamidomethylbutyrolactones. The reaction presumably proceeds via an aziridine intermediate, which could be isolated in one case.

β-Silyl styrene as a dienophile in the cycloaddition with 3,5-dibromo-2-pyrone for the total synthesis of (±)-pancratistatin

A new synthetic route to (±)-pancratistatin was devised utilizing β-silyl styrene as a dienophile in the cycloaddition with 3,5-dibromo-2-pyrone. The TMS group incorporated in the cycloadduct permitted a facile elimination process for the eventual installation of the C(1)-OH function. Subsequent transformations including Curtius rearrangement and Bischler-Napieralski reactions completed the total synthesis of (±)-pancratistatin.

Synthesis of (+)-lycoricidine by the application of oxidative and regioselective ring-opening of aziridines

A highly stereoselective total synthesis of (+)-lycoricidine has been described. The salient features of this synthesis are the one-pot elimination followed by allylation reaction, ring-closing metathesis, stereoselective aziridine formation, Dess-Martin periodinane, and silica gel mediated oxidative ring-opening of aziridine to form alpha,beta-unsaturated ketone (allyl amine) and intramolecular Heck cyclization.

Total synthesis of (+/-)-powelline and (+/-)-buphanidrine

The total synthesis of (+/-)-powelline (13 linear steps in an overall yield of 6%) and (+/-)-buphanidrine (14 linear steps and a 6% overall yield) and has been achieved using a novel approach to the crinane skeleton. An organocatalytic oxidative coupling allowed direct construction of the key quaternary carbon-to-aryl bond in high yield allowing rapid access to the target alkaloids.

Potent and selective inhibition of human cytochrome P450 3A4 by seco-pancratistatin structural analogs

seco-Derivatives of the anticancer agent pancratistatin bearing the 2S,3S,4S,5S configuration were accessed via a novel, highly diastereoselective anti-aldol reaction. Structure-activity relationships reveal important insights into the seco-pancratistatin pharmacophore as a potent and selective inhibitor of human cytochrome P450 3A4 (CYP3A4), and highlight features of concern in advancing a potent, selective anticancer agent in the pancratistatin series.

Structure-activity studies on seco-pancratistatin analogs: potent inhibitors of human cytochrome P450 3A4

Two total syntheses of fully functionalized seco-analogs of the anticancer compound pancratistatin are reported. Structure-activity relationship (SAR) studies identified potent and selective inhibitors of human cytochrome P450 3A4 (CYP3A4) and revealed several core pharmacophoric elements. These studies identify potential roadblocks and will guide the further development of a viable selective clinical pancratistatin derivative.

Antineoplastic agents. 454. Synthesis of the strong cancer cell growth inhibitors trans-dihydronarciclasine and 7-deoxy-trans-dihydronarciclasine (1a)

To further pursue the antineoplastic leads offered by our isolation of trans-dihydronarciclasine (1a) and 7-deoxy-trans-dihydronarciclasine (1c) from two medicinal plant species of the Amaryllidaceae family, a practical palladium-catalyzed hydrogenation procedure was developed for the synthesis of these isocarbostyrils from narciclasine (2a) and 7-deoxynarciclasine (2c).

Catalytic asymmetric synthesis using feedstocks: an enantioselective route to 2-arylpropionic acids and 1-arylethyl amines via hydrovinylation of vinyl arenes

A three-step procedure for the synthesis of 2-arylpropionic acids (profens) from vinyl arenes in nearly enantiomerically pure form has been developed. Excellent yields (>97%), regioselectivities (>99%), and enantioselectivities (>97% ee) for the desired branched products were obtained in the asymmetric hydrovinylation reactions of vinyl arenes, and the products from these reactions were transformed into 2-arylpropionic acids via oxidative degradation. Subsequent Curtius or Schmidt rearrangements of these acids provided highly valued 1-arylethyl amines, including a prototypical primary amine with an alpha-chiral tertiary N-alkyl group, in very good yields.

Application of palladium-catalyzed allylic arylation to the synthesis of a (+/-)-7-deoxypancratistatin analogue

Palladium-catalyzed coupling of an aryl siloxane and an allylic carbonate proceeded in good yield to give an adduct that was converted to an analogue of (+/-)-7-deoxypancratistatin.

Synthesis of some members of the hydroxylated phenanthridone subclass of the Amaryllidaceae alkaloid family

The total synthesis of several members of the hydroxylated phenanthridone subclass of the Amaryllidaceae alkaloid family has been carried out. (+/-)-Lycoricidine and (+/-)-7-deoxypancratistatin were assembled through a one-pot Stille/intramolecular Diels-Alder cycloaddition cascade to construct the core skeleton. The initially formed [4+2]-cycloadduct undergoes nitrogen-assisted ring opening followed by a deprotonation/reprotonation of the resulting zwitterion to give a rearranged hexahydroindolinone on further heating at 160 degrees C. The stereochemical outcome of the IMDAF cycloaddition has the side arm of the tethered vinyl group oriented exo with respect to the oxygen bridge. The resulting cycloadduct was used for the stereocontrolled installation of the remaining functionality present in the C-ring of the target molecules. Key features of the synthetic strategy include (1) a lithium hydroxide induced tandem hydrolysis/decarboxylation/elimination sequence to introduce the required pi-bond in the C-ring of (+/-)-lycoricidine, and (2) conversion of the initially formed Diels-Alder adduct into an aldehyde intermediate which then undergoes a stereospecific decarbonylation reaction mediated by Wilkinson's catalyst to set the trans-B-C ring junction of (+/-)-7-deoxypancratistatin.

A solution to the stereochemical problems posed by amaryllidaceae constituents using a highly syn-selective arylcuprate conjugate addition to γ-amino and γ-carbamato-α,β-enoates

Various substituted arylcuprates undergo stereocontrolled additions to L-serine-derived γamino- and γ-carbamato-α,β-enoates with high syn-selectivities. The stereochemical outcome of these reactions is fully consistent with the reductive elimination-based model proposed previously. This method is well suited for the preparation of a broad range of biologically active amaryllidaceae constituents and their aromatic analogues.

An efficient synthesis of (+/-)-Lycoricidine featuring a Stille-IMDAF cycloaddition cascade

[reaction: see text] A highly efficient total synthesis of (+/-)-Lycoricidine is described. The synthesis features the ready preparation of the Lycoricidine skeleton by a Stille-IMDAF cycloaddition cascade. The resulting cycloadduct is then used for the stereocontrolled installation of the other functionality present in the C-ring of the target molecule.

A synthesis of 3-deoxydihydrolycoricidine: Refinement of a structurally minimum pancratistatin pharmacophore

The synthesis of 3-deoxydihydrolycoricidine, a key element toward elucidation of the pancratistatin anticancer pharmacophore, is described. Biological evaluation of this compound showed it to be significantly less active against tumor cells than pancratistatin. In addition to those features previously identified, the requirement of a 2,3,4-triol functionalized ring-C is now definitely established as the minimum pharmacophoric element for potent anticancer activity.

Pancratistatin causes early activation of caspase-3 and the flipping of phosphatidyl serine followed by rapid apoptosis specifically in human lymphoma cells

Recently a major research effort has been focused on the development of anticancer drugs by targeting the components of a biochemical pathway to induce apoptosis in cancerous cells. Some of the natural products (e.g. paclitaxel) have been proven to be useful in inducing apoptosis in cancer cells with limited specificity. Pancratistatin, a natural product isolated and characterized over a decade ago, has been shown to be cytostatic and antineoplastic. We investigated the specificity and biochemical mechanism of action of pancratistatin. Pancratistatin seemed to show more specificity than VP-16 or paclitaxel as an efficient inducer of apoptosis in human lymphoma (Jurkat) cells, with minimal effect on normal nucleated blood cells. Caspase-3 activation and exposure of phosphatidyl serine on the outer leaflet of the plasma membrane were earlier events than the generation of ROS and DNA fragmentation observed following pancratistatin treatment. This indicates a possible involvement of caspase-3 and plasma membrane proteins in the induction phase of apoptosis. Our results indicate that pancratistatin does not cause DNA double-strand breaks or DNA damage prior to the execution phase of apoptosis in cancer cells. Parallel experimentation with VP-16, a currently used medication for cancer treatment, indicated that VP-16 causes substantial DNA damage in normal non-cancerous blood cells, while pancratistatin does not cause any DNA double-strand breaks or DNA damage in non-cancerous cells. Taken together, our finding that pancratistatin induces apoptosis in cancer cells using non-genomic targets, and more importantly does not seem to have any affect non-cancerous cells, presents a significant platform to develop non-toxic anticancer therapies.

Synthesis and biological activity of some structural modifications of pancratistatin

Structurally modified derivatives of 7-deoxypancratistatin have been synthesized and evaluated in cancer cell line inhibition studies.

Total Synthesis of Pancratistatin Relying on the [3,3]-Sigmatropic Rearrangement

A new total synthesis of the antitumor alkaloid, pancratistatin (1), has been accomplished from readily available starting materials. Claisen rearrangement of the racemic dihydropyranethylene 17 was employed to construct the A and C rings with the appropriate stereochemistry. In addition, the Ireland-Claisen rearrangement of the enantiomerically pure 9 followed by ring-closing metathesis provided the important intermediate 24, thus implying that our approach could yield the enantioselective synthesis of (+)-pancratistatin. With the appropriately functionalized cyclohexene 24, stereo- and regiocontrolled functional group interchanges, such as iodolactonization, dihydroxylations, and a cyclic sulfate elimination reaction, facilitated the production of the target natural product.