Synthesis of Amaryllidaceae Constituents and Unnatural Derivatives

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.

Short Formal Syntheses of Lycorine and Congeners Using a 5-Endo-Trig/6-Endo-Trig Radical Cyclization Sequence

Here, we report a practical route to medicinally interesting lycorine congeners alongside formal syntheses of various lycorine-type natural products, including lycorine itself. The efficiency of our strategy derives from a back-to-back 5-endo-trig/6-endo-trig radical cyclization sequence, which we systematically studied both experimentally and computationally. The results of our work will facilitate future development of urgently needed antiviral therapeutics based on lycorine.

Regioselective SmI2-Mediated Radical ipso-Substitution Cyclization for the Construction of Pyrrolophenanthridinone Skeletons: The Synthesis of Amaryllidaceae Alkaloids

Here, we report a regioselective, samarium(II) diiodide mediated intramolecular radical ipso-substitution cyclization. Through the use of a methoxy group as a leaving group, it was possible to regulate the regioselectivity of the reaction by changing the temperature and additives. We applied the developed reaction to the synthesis of four Amaryllidaceae alkaloids and have shown that the present reaction successfully overcomes regioselectivity issues encountered with other cyclization methods.

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.

Lactate metabolism in rheumatoid arthritis: Pathogenic mechanisms and therapeutic intervention with natural compounds

BACKGROUND

Rheumatoid arthritis (RA) is a common chronic and systemic autoimmune disease characterized by persistent inflammation and hyperplasia of the synovial membrane, the degradation of cartilage, and the erosion of bones in diarthrodial joints. The inflamed joints of patients with RA have been recognized to be a site of hypoxic microenvironment which results in an imbalance of lactate metabolism and the accumulation of lactate. Lactate is no longer considered solely a metabolic waste product of glycolysis, but also a combustion aid in the progression of RA from the early stages of inflammation to the late stages of bone destruction.

PURPOSE

To review the pathogenic mechanisms of lactate metabolism in RA and investigate the potential of natural compounds for treating RA linked to the regulation of imbalance in lactate metabolism.

METHODS

Research advances in our understanding of lactate metabolism in the pathogenesis of RA and novel pharmacological approaches of natural compounds by targeting lactate metabolic signaling were comprehensively reviewed and deeply discussed.

RESULTS

Lactate produced by RA synovial fibroblasts (RASFs) acts on targeted cells such as T cells, macrophages, dendritic cells and osteoclasts, and affects their differentiation, activation and function to accelerate the development of RA. Many natural compounds show therapeutic potential for RA by regulating glycolytic rate-limiting enzymes to limit lactate production, and affecting monocarboxylate transporter and acetyl-CoA carboxylase to inhibit lactate transport and conversion.

CONCLUSION

Regulation of imbalance in lactate metabolism offers novel therapeutic approaches for RA, and natural compounds capable of targeting lactate metabolic signaling constitute potential candidates for development of drugs RA.

Catalytic, Asymmetric Total Synthesis of (+)-α-, (+)-β-, (+)-γ-, and (-)-δ-Lycorane

The first collectively asymmetric total synthesis of all members of lycorane, including (+)-α, (+)-β, (+)-γ, and (-)-δ, in a catalytic manner has been achieved. The cornerstone of this synthesis features an asymmetric, stereodivergent Ir/amine dual catalytic α-allylation of 2-phthalimidoacetaldehyde.

Synthesis and biological evaluation of 10-benzyloxy-Narciclasine

A chemoenzymatic convergent synthesis of 10-benzyloxy narciclasine from bromobenzene was accomplished in 16 steps. The key transformations included toluene dioxygenase-mediated hydroxylation, nitroso Diels-Alder reaction and intramolecular Heck cyclization. The unnatural derivative of narciclasine was subjected to biological evaluation and its activity was compared to other C-10 and C-7 compounds prepared previously.

From Glycals to Nitrogen Heterocycles and Carbocycles via "Cleavage-Intramolecular Recombination Strategy"

Glycals (carbohydrate enol-ethers) have enjoyed profound applications in organic synthesis for more than a century. They not only serve as versatile glycosyl donors or as substrates for Ferrier rearrangement, but also find extensive synthetic applications especially as a "chiral pool" for accomplishing the synthesis of a variety of natural and biologically important compounds. As cyclic enol ethers, they demonstrate high reactivity and are among the most and variously transformable monosaccharide derivatives. The uniqueness of the reactivity of glycals is that they can be synthetically tuned to get a library of derivatives through stereo- and regioselective introduction of a variety of functional groups at C1, C2, C3 as well as C4 carbons of the sugar. We have developed a practical approach for stereoselective mono- and diamination of glycals and over the years utilized these scaffolds for the synthesis of a variety of biologically important nitrogen heterocycles and carbocycles through a "Diversity Oriented Approach". Our synthetic strategy in this direction mainly relied on the cleavage of ring O-C bond of the sugar followed by an "intramolecular recombination" reaction. Utilizing this strategy, we have accomplished the synthesis of several biologically important natural products, their analogues and related unnatural derivatives. Examples of such compounds reported from our group include polyhydroxypyrrolidines, DMDP, anisomycin, steviamine, pochonicine, conduramines, bulgecinine, aminocyclitols, azepanes, 4-hydroxy-D-proline, azanucleosides and their analogues. A personal account highlighting these syntheses is presented here.

Asymmetric Hydrogenation of Racemic 6-Aryl 1,4-Dioxaspiro[4.5]decan-7-ones to Functionalized Chiral β-Aryl Cyclohexanols via a Dynamic Kinetic Resolution

A ruthenium-catalyzed asymmetric hydrogenation method for the synthesis of functionalized β-aryl cyclohexanols is described. With chiral spiro ruthenium catalyst (R_a,S,S)-5c, a series of racemic α-aryl cyclohexanones bearing a β-monoethylene ketal group were hydrogenated to the corresponding functionalized β-aryl cyclohexanols in high yields with enantioselectivity of up to 99% ee via a dynamic kinetic resolution. This protocol can be conducted on a decagram scale and provide potential approaches for the synthesis of optically active and densely functionalized aryl cyclohexanols.

Palladium-Catalyzed Stereoselective Aza-Wacker-Heck Cyclization: One-Pot Stepwise Strategy toward Tetracyclic Fused Heterocycles

Palladium-catalyzed intramolecular tandem cyclization reactions were conducted for the synthesis of densely cis/cis-fused aza-tetracyclic structures. The process involved a palladium(II)-catalyzed aerobic aza-Wacker reaction, followed by a palladium(0)-catalyzed Heck reaction. The effects of the solvent and benzene substitution pattern on the one-pot, two-step cascade reaction were studied systematically, and a probable mechanism was proposed. Strained pentahydrobenzo[f]cyclopenta[hi]indolizin-6-one and racemic γ-lycorane can also be synthesized rapidly using this palladium-catalyzed aza-Wacker-Heck cyclization reaction.

Total Synthesis of (+)-Lycoricidine and Conduramine B-1, ent-C-1, C-4, D-1, ent-F-1, and ent-F-4, and Formal Synthesis of (-)-Laminitol: a C2-Symmetric Chiral-Pool-Based Flexible Strategy

A facile and diversity-oriented synthetic strategy toward aminocyclitol natural products from inexpensive C₂-symmetric l-tartaric acid was developed. The pivotal epoxide was used as a common intermediate to accomplish eight diverse target molecules in six to eleven steps. Various allyl-amine-type conduramines were synthesized in a diastereoselective manner. Heck arylation was explored to construct a phenanthridone ring in a concise synthesis of (+)-lycoricidine. In addition, a highly efficient formal synthesis of (-)-laminitol was developed.

(±)-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.

Borges W, Lacerda V. Cytotoxic and Genotoxic Activities of Alkaloids from the Bulbs of Griffinia gardneriana and Habranthus itaobinus (Amaryllidaceae)

Background:

Amaryllidaceae plants are known to be a great source of alkaloids, which are considered an extensive group of compounds encompassing a wide range of biological activities. The remarkable cytotoxic activities observed in most of the Amaryllidaceae alkaloids derivatives have prompt the chemical and biological investigations in unexplored species from Brazil.

Objective:

To evaluate the cytotoxic and genotoxic properties of alkaloids of Griffinia gardneriana and Habranthus itaobinus bulbs and study the role of caspase-3 as a molecular apoptosis mediator.

Methods:

Methanolic crude extracts of Griffinia gardneriana and Habranthus itaobinus bulbs were submitted to acid-base extraction to obtain alkaloid-enriched fractions. The obtained fractions were fractionated using chromatographic techniques leading to isolation and identification of some alkaloids accomplished via HPLC and 1H-NMR, respectively. Molecular docking studies assessed the amount of free binding energy between the isolated alkaloids with the caspase-3 protein and also calculated the theoretical value of Ki. Studies have also been developed to evaluate in vitro cytotoxicity and genotoxicity in such alkaloids and apoptosis activation via the caspase pathway using both tumor and normal cell lines.

Results:

Seven alkaloids were isolated and identified. Among these, 11-hydroxyvittatine and 2-α-7- dimethoxyhomolycorine were not cytotoxic, whereas tazettine, trisphaeridine, and sanguinine only showed activity against the fibroblast lineage. Lycorine and pretazettine were 10 to 30 folds more cytotoxic than the other alkaloids, including cancerous lines, and were genotoxic and capable of promoting apoptosis via the caspase-3 pathway. This result supports data obtained in docking studies wherein these two compounds exhibited the highest free energy values.

Conclusion:

The cytotoxicity assay revealed that, among the seven alkaloids isolated, only lycorine and pretazettine were active against different cell lines, exhibiting concentration- and time-dependent cytotoxic actions alongside genotoxic action and the ability to induce apoptosis by caspase-3, a result consistent with those obtained in docking studies.

Ring closing metathesis (RCM) approach to the synthesis of conduramine B-2, ent-conduramine F-2, aminocyclopentitol and trihydroxyazepane

The syntheses of conduramine B-2, ent-conduramine F-2, aminocyclopentitol and trihydroxyazepane were accomplished from a common precursor, through a divergent approach using ring closing metathesis (RCM) as the key step. Tri-O-benzyl-d-glucal was converted to 3,4,6-tri-O-benzyl-1,2-dideoxy-2-iodo-1-p-toluenesulfonamido-α-d-mannose. Exposure to NaBH4 in MeOH resulted in a facile 1,2-transposition of the -NHTs group with concomitant glycosylation to give methyl 3,4,6-tri-O-benzyl-2-deoxy-2-p-toluenesulfonamido-β-d-glucoside, which was converted into methyl 6-deoxy-6-iodo-glucoside in three steps. Zinc-mediated Vasella's rearrangement proceeded smoothly to give the pluripotent formyl-olefin, possessing both electrophilic and nucleophilic sites, which was used as a common precursor in our diversity-oriented approach. Vinylation of the carbonyl group followed by RCM and subsequent deprotection resulted in the successful synthesis of conduramine B-2 and ent-conduramine F-2 for the first time. On the other hand, the Wittig reaction of the formyl-olefin affords the diene that undergoes Grubbs' I catalyzed RCM and deprotection/reduction to provide 3-amino-cyclopentan-1,2-diol. Utilizing the nucleophilic site at the nitrogen of the common precursor, base mediated N-allylation was carried out to obtain the corresponding diene that underwent a smooth RCM to afford trihydroxyazepane.

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.

Amaryllidaceae andSceletiumalkaloids

Recent progress on the isolation, identification, biological activity and synthetic studies of Amaryllidaceae alkaloids, as well as the structurally close alkaloids from theSceletiumgenus, published from July 2015 to June 2017 are reviewed.

Recent advances in the total synthesis of gracilamine

Gracilamine belongs to the Amaryllidaceae alkaloid group and has a unique five-ring skeleton. Its scarcity in plants limits biological studies on it. A number of synthetic chemists have carried out the total synthesis of gracilamine in the past few years. This review will summarize the synthetic studies of gracilamine, and hopes to bring new inspiration to the research of Amaryllidaceae alkaloids.

Lycorine inhibits melanoma A375 cell growth and metastasis through the inactivation of the PI3K/AKT signaling pathway

Malignant melanoma, one of the most aggressive skin cancers, has a very high mortality rate. Currently, the number of drugs to treat melanoma is low. Although new immunotherapeutic approaches based on the use of antibodies against immune checkpoints have shown long term responses, it is urgent to develop novel anti-melanoma drugs with a high efficiency and a low toxicity in a large number of patients. Lycorine, a natural product, has been reported to exert antitumor effects on some cancers. However, the impact of lycorine on melanoma cells is still unknown. Using the CCK8 assay, we found that lycorine can suppress the proliferation of melanoma A375 cells in a dose-time-dependent manner. Moreover, a transwell assay showed that lycorine inhibited the migration and invasion of A375 cells significantly. Further, lycorine treatment could induce the apoptosis of the A375 cells. Biochemical analyses showed that the expression level of the anti-apoptosis Bcl-2 protein decreased, while the expression of the pro-apoptosis protein Bax and active caspase-3 increased after lycorine treatment. Finally, using western blot assay, we found that the antitumor effects of lycorine on A375 cells might be through the inactivation of the PI3K/Akt signaling pathway. Based on these observations, we suggest that lycorine may be an interesting candidate for further studies on its ability to represent a novel antitumor drug for human melanoma treatment in the future.

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.

Isolation, Synthesis, and Semisynthesis of Amaryllidaceae Constituents from Narcissus and Galanthus sp.: De Novo Total Synthesis of 2- epi-Narciclasine

An efficient protocol for the isolation of narciclasine from common Amaryllidaceae bulbs, separation from haemanthamine, and the occurrence of a trace alkaloid, 2- epi-narciclasine, are reported. Attempts to convert natural narciclasine to its C-2 epimer by Mitsunobu inversion or oxidation/reduction sequences were compromised by rearrangement and aromatization processes, through which a synthesis of the alkaloid narciprimine was achieved. The methylation of the 7-hydroxy group of natural narciclasine followed by protection of the 3,4-diol function and oxidation/reduction sequence provided the target C-2 epimer. A de novo chemoenzymatic synthesis of 2- epi-narciclasine from m-dibromobenzene is also described. Haemanthamine and narciprimine were readily detected in the crude extracts of Narcissus and Galanthus bulbs containing narciclasine, and the occurrence of 2- epi-narciclasine as a trace natural product in Galanthus sp. is reported for the first time.

Total Synthesis of (±)-Crinane from 6,6-Dibromobicyclo[3.1.0]hexane Using a 5- exo- trig Radical Cyclization Reaction to Assemble the C3a-Arylated Perhydroindole Substructure

Crinane embodies the tetracyclic framework associated with some of the most common Amaryllidaceae alkaloids. It has now been prepared in 10 steps from 6,6-dibromobicyclo[3.1.0]hexane (2). The initial step involves the thermally induced electrocyclic ring opening of cyclopropane 3 and capture of the resulting π-allyl cation with benzylamine to give an allylic amine that is readily elaborated to the 3°-amine 10. This last compound was engaged in a 5- exo- trig free radical cyclization reaction to give the C3a-arylated perhydroindole 11. Compound 11 was then converted, over two steps, into (±)-crinane, the hydrochloride salt of which has been subjected to single-crystal X-ray analysis.

Nickel-Catalyzed Dearomative trans-1,2-Carboamination

We describe the development of an arenophile-mediated, nickel-catalyzed dearomative trans-1,2-carboamination protocol. A range of readily available aromatic compounds was converted to the corresponding dienes using Grignard reagents as nucleophiles. This strategy provided products with exclusive trans-selectivity and high enantioselectivity was observed in case of benzene and naphthalene. The utility of this methodology was showcased by controlled and stereoselective preparation of small, functionalized molecules.

Asymmetric cinnamylation of N-tert-butanesulfinyl imines with cinnamyl acetates: total syntheses of (+)-lycoricidine and (+)-7-deoxypancratistatin

Highly diastereoselective palladium catalyzed cinnamylation of N-tert-butanesulfinyl imines with cinnamyl acetates has been established to provide enantioenriched β-aryl homoallylic amines. The synthetic application of this stragety has been successfully demonstrated in the concise total syntheses of antitumor natural products (+)-lycoricidine and (+)-7-deoxypancratistatin.

A Review on Recent Syntheses of Amaryllidaceae Alkaloids and Isocarbostyrils (Time period mid-2016 to 2017)

Alkaloids from the Amaryllidaceae have become valuable targets for synthetic organic chemists, mainly due to their wide variety of bioactivities and potential for utilization in medicinal chemistry ventures. In addition, the structural complexity of a number of these alkaloids has also been a reason for the interest in these compounds. In this review, the last 18 months of literature was perused and synthetic highlights have been presented here, with the hope to further focus attention on this interesting class of compounds and to encourage others to synthesize these compounds and their derivatives and/or analogues. The review contains examples of syntheses from most of the important alkaloid scaffold classes previously isolated from the Amaryllidaceae, namely: lycorine, crinine, galanthamine, tazettine, montanine, phenanthridone, phenanthridine, plicamine, mesembrine and some minor scaffolds (like gracilamine).

Potential Deoxycytidine Kinase Inhibitory Activity of Amaryllidaceae Alkaloids: An In Silico Approach

Background:

Plants of the Amaryllidaceae family have been under intense scrutiny for the presence of a couple of alkaloidal secondary metabolites with endued cytotoxic activity, such as pancratistatin (1), 7-deoxypancratistatin (2), narciclasine (3), 7-deoxynarciclasine (4), trans-dihydronarciclasine (5), and 7-deoxy-trans-dihydronarciclasine (6). Nevertheless, preclinical evaluation of these alkaloids has been put on hold because of the limited quantity of materials available from isolation.

Aim:

To explore the underlying cytotoxic molecular mechanisms of the Amaryllidaceae alkaloids (1–6) and to assess their absorption, distribution, metabolism, excretion, and toxicity (ADMET) profiles using chemoinformatic tools.

Materials And Methods:

AutoDock 4.0 software along with different in silico chemoinformatic tools, namely PharmMapper, Molinspiration, MetaPrint2D, and admetSAR servers, were used to assess the drugability of the Amaryllidaceae alkaloids (1–6).

Results:

Deoxycytidine kinase (dCK) (PDB: 1P60) was predicted as a potential target with fitting score of 5.574. In silico molecular docking of (1–6) into dCK revealed good interactions, where interesting hydrogen bonds were observed with the amino acid residues—Gly-28 and Ser-35—located in the highly conserved P-loop motif. This motif plays a special role in dCK function. Contrary to (1), in silico pharmacokinetic results have shown good absorption and permeation and thus good oral bioavailability for (2–6).

Conclusion:

The in silico docking data have proposed that the reported cytotoxic activity of the Amaryllidaceae alkaloids (1–6) could be mediated through dCK inhibition. In addition, the ADMET profile of these alkaloids is promising and thus (1–6) could be candidates for future drug development.

Total Synthesis of Lycoricidine and Narciclasine by Chemical Dearomatization of Bromobenzene

The total synthesis of lycoricidine and narciclasine is enabled by an arenophile-mediated dearomative dihydroxylation of bromobenzene. Subsequent transpositive Suzuki coupling and cycloreversion deliver a key biaryl dihydrodiol intermediate, which is rapidly converted into lycoricidine through site-selective syn-1,4-hydroxyamination and deprotection. The total synthesis of narciclasine is accomplished by the late-stage, amide-directed C-H hydroxylation of a lycoricidine intermediate. Moreover, the general applicability of this strategy to access dihydroxylated biphenyls is demonstrated with several examples.

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.

The First Enantioselective Total Synthesis of (-)-trans-Dihydronarciclasine

A feasible and enantioselective total synthesis of (-)-trans-dihydronarciclasine [(-)-1], a highly biologically active alkaloid, was devised starting from vanillin (8). The key step of this new synthesis was an asymmetric, organocatalytic Michael addition, in which an optically active nitropentanone [(-)-13] was obtained from a butenone derivative (12). Excellent enantioselectivity (>99% ee) was achieved using the (8S,9S)-9-amino(9-deoxy)epiquinine (16) organocatalyst. The target molecule can be prepared in 13 steps from compound (-)-13. The total synthesis has provided a facile and first access to the ent-form of naturally occurring (+)-trans-dihydronarciclasine, a highly potent cytostatic alkaloid.

Asymmetric Syntheses of Amaryllidaceae Alkaloids (-)-Crinane and (+)-4a-Dehydroxycrinamabine

A palladium-catalyzed asymmetric allyl-allyl cross-coupling reaction to construct the chiral quaternary carbon center of crinane alkaloids has been developed. On the basis of an efficient approach, the enantioselective synthesis of (-)-crinane (1) is presented, and the first asymmetric total synthesis of (+)-4a-dehydroxycrinamabine (2) was achieved by subsequent oxidation, 1,4-conjugate addition, RCM reaction, reductive amination, and Pictet-Spengler reaction. The method provided an alternative strategy for the syntheses of crinane alkaloids and other Amaryllidaceae natural products.