Lycoricidinol and lycoricidine, new plant-growth regulators in the bulbs of Lycoris radiata herb

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.

Identification of haemanthamine as a phytotoxic alkaloid in Narcissus pseudonarcissus L. (Daffodil) emerging buds

Emerging buds of Narcissus pseudonarcissus were found to accumulate the alkaloid haemanthamine (1) at high concentrations, exceeding that of narciclasine (2), the most abundant constituent in bulbs of the plant. A phytoactivity screening assay demonstrated the novel phytotoxicity of haemanthamine against Raphanus sativus (radish), Lactuca sativus (lettuce), Triticum aestivum (red wheat), Solanum lycopersicum (tomato), Cucumis sativus (cucumber), Ipomoea (Morning glory), and Lens culinaris (lentil). Haemanthamine (1) phytotoxicity was found to exceed that of the commercial herbicide glyphosate and less toxic than narciclasine (2).

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.

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.

Ni-Catalyzed Reductive and Merged Photocatalytic Cross-Coupling Reactions toward sp3/sp2-Functionalized Isoquinolones: Creating Diversity at C-6 and C-7 to Address Bioactive Analogues

Naturally occurring isoquinolones have gained considerable attention over the years for their bioactive properties. While the late-stage introduction of various functionalities at certain positions, namely, C-3, C-4, and C-8, has been widely documented, the straightforward introduction of challenging sp3 carbon-linked acyclic aminoalkyl or aza- and oxacyclic appendages at C-6 and C-7 remains largely underexplored. Interest in 6-substituted azacyclic analogues has recently garnered attention in connection with derivatives exhibiting anticancer activity. Reported here is the first application of the versatile and recently emerging field of Ni-catalyzed reductive cross-coupling reactions to the synthesis of 6- and 7- hetero(cyclo)alkyl-substituted isoquinolones. In a second and complementary approach, a new set of C-6- and C-7-substituted positional isomers of hetero(cyclo)alkyl appendages were obtained from the merging of photocatalytic and Ni-catalyzed coupling reactions. In both cases, 6- and 7-bromo isoquinolones served as dual-purpose reacting partners with readily available tosylates and carboxylic acids, respectively.

Chemodiversity, chemotaxonomy and chemoecology of Amaryllidaceae alkaloids

The Amaryllidaceae alkaloids are a distinctive chemotaxonomic feature of the subfamily Amaryllidoideae of the family Amaryllidaceae, which consists of 59 genera and >800 species distributed primarily in tropical and subtropical areas. Since the first isolation, ca. 140 ago, >600 structurally diverse Amaryllidaceae alkaloids have been reported from ca. 350 species (44% of all species in the subfamily). A few have been found in other plant families, but the majority are unique to the Amaryllidoideae. These alkaloids have attracted considerable research interest due to their wide range of biological and pharmacological activities, which have been extensively reviewed. In this chapter we provide a review of the 636 structures of isolated or tentatively identified alkaloids from plants of the Amaryllidoideae and their classification into 42 skeleton types, as well as a discussion on their distribution, and chemotaxonomical and chemoecological aspects.

Synthesis of (-)-Conduramine A1, (-)-Conduramine A2 and (-)-Conduramine E2 in Six Steps from Cyclohexa-1,4-diene

A method to enable the synthesis of conduramines and their N-substituted derivatives (enantiopure or racemic form) in six steps (five steps for N-substituted derivatives) from cyclohexa-1,4-diene is reported. Key features of this reaction sequence include a preparation of benzene oxide that is amenable to multigram scale, and its efficient ring-opening upon treatment with a primary amine. Epoxidation of the resultant amino alcohols (40% aq HBF₄ then m-CPBA) is accompanied by hydrolytic ring-opening in situ to give the corresponding N-substituted conduramine derivatives directly. These may undergo subsequent N-deprotection to give the parent conduramines, as demonstrated by the preparation of enantiopure (-)-conduramine A1, (-)-conduramine A2, and (-)-conduramine E2 (the latter two for the first time). The selectivity of the epoxidation reaction is proposed to be the result of competitive ammonium-directed and hydroxyl-directed epoxidation processes, followed by either direct (S_N2-type) or conjugate (S_N2'-type) ring-openings of the intermediate epoxides.

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.

Identification of narciclasine from Lycoris radiata (L'Her.) Herb. and its inhibitory effect on LPS-induced inflammatory responses in macrophages

Lycoris radiata (L'Her.) Herb. (L. radiata) was traditionally used as a folk medicine in China for treatment of Alzheimer's disease. However, the specific component responsible for its considerable toxicity remained unclear thus restricting its clinical trials. Narciclasine (NCS) was isolated from L. radiata and treatment of NCS for 72 h exhibited significant antiproliferative effects against L02, Hep G2, HT-29 and RAW264.7 cells. However, what needs to be emphasized is that at safe working concentrations of 0.001-0.016 μM, administration of NCS for 24 h inhibited the mRNA expression of inducible nitric oxide synthase (iNOS), interleukin-6 (IL-6), tumor necrosis factor-alpha (TNF-ɑ), interleukin-1beta (IL-1β) and cyclooxygenase-2 (COX-2) in lipopolysaccharide (LPS)-induced macrophages thereby suppressing production of nitric oxide (NO), IL-6, TNF-ɑ and IL-1β. NCS supplementation also inhibited nuclear factor-kappa B (NF-κB) activation by suppressing NF-κB P65 phosphorylation and nuclear translocation, IκBɑ degradation and phosphorylation, and IκKɑ/β phosphorylation. The phosphorylation of c-Jun N-terminal kinase (JNK) and P38, and expression of COX-2 was also attenuated by NCS. These results suggested that NCS might exert anti-inflammatory effects through inhibiting NF-κB and mitogen-activated protein kinase (MAPK) pathways even at very low doses.

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.

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.

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.

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.

Biological evaluation of ent-narciclasine, ent-lycoricidine, and certain enantiomerically-related congeners

The non-natural enantiomeric forms of narciclasine and lycoricidine ((-)-1 and (-)-2, respectively), as well as congeners 3-6 are available through chemoenzymatic synthesis. Accordingly, they have now been tested for their cytotoxic effects in a 13-member human cancer cell-line panel and found to be only weakly active. In contrast, an authentic sample of the natural enantiomeric form of narciclasine ((+)-1) was found to be highly active in the same screens.

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).

Amaryllidaceae isocarbostyril alkaloids and their derivatives as promising antitumor agents

This review covers the isolation, total synthesis, biologic activity, and more particularly the in vitro and in vivo antitumor activities of naturally occurring isocarbostyril alkaloids from the Amaryllidaceae family. Starting from these natural products, new derivatives have been synthesized to explore structure-activity relationships within the chemical class and to obtain potential candidates for preclinical development. This approach appears to be capable of providing novel promising anticancer agents.

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.

Synthesis of 5(6H)-Phenanthridones Using Diels-Alder Reaction of 3-Nitro-2(1H)-quinolones Acting as Dienophiles

Diels-Alder reactions of 3-nitro-2(1H)-quinolones with 1,3-butadiene derivatives were carried out to give the phenanthridone derivatives under both atmospheric and high pressure conditions. Furthermore, the reactivity of 3-substituted 2(1H)-quinolones acting as a dienophile with 2,3-dimethyl-1,3-butadiene was examined using molecular orbital (MO) calculation.

Isolation and structural modification of 7-deoxynarciclasine and 7-deoxy-trans-dihydronarciclasine

As an extension of structure-activity relationship studies of pancratistatin (1), various techniques were first evaluated for separating the mixtures of 7-deoxynarciclasine (2b) and 7-deoxy-trans-dihydronarciclasine (3a) isolated from Hymenocallis littoralis. An efficient solution for that otherwise difficult separation then allowed the lactam carbonyl group of protected (4c and 5c) alcohols 2b and 3a to be reduced employing lithium aluminum hydride. Cleavage (TBAF followed by H2SO4) of the silyl ester/acetonide protected 6a gave amine 8. X-ray crystal structure determinations were employed to confirm the structures of 3,4-acetonide-5-aza-6-deoxynarciclasine (6b), 5-aza-6-deoxynarciclasine (8a), and 5-aza-6-deoxy-trans-dihydronarciclasine (9a, 9b). Against the murine P388 lymphocytic leukemia and a panel of human cancer cell lines, the parent natural products, 7-deoxynarciclasine (2b) and 7-deoxy-trans-dihydronarciclasine (3a), were found to generally be more cancer cell growth inhibitory (GI50 0.1 to <0.01 microg/mL) than the compounds with structural modifications such as amine 8 by a factor of 10 or more. The trans ring juncture of isocarbostyril 3a proved to be an important modification of narciclasine (2a) for improving cancer cell growth inhibition in this series.

Novel Diels-Alder Reaction of 4-Nitro-1(2H)-isoquinolones

A novel Diels-Alder (DA) reaction with 4-nitro-1(2H)-isoquinolones acting as the dienophile afforded 5(6H)-phenanthridone derivatives. The DA reaction of 4-nitro-1(2H)-isoquinolone with 1-methoxy-1,3-butadiene gave biologically active 5(6H)-phenanthridone possessing in a high yield. Regioselectivity of 4-nitro-1(2H)-isoquinolones with 1-methoxy-3-silyloxy-1,3-butadiene was calculated using molecular orbital (MO) calculations.

Rh(I)-Catalyzed Ring Opening of an IMDAF-Derived Oxabicyclo Cycloadduct as the Key Step in the Synthesis of (±)-epi-Zephyranthine

[reaction: see text] A new strategy for epi-zephyranthine has been developed that is based in part on an extraordinarily facile intramolecular Diels-Alder reaction of a 2-imido-substituted furan. By using a Rh(I)-catalyzed ring opening of the resulting oxabicyclic adduct, the cis-diol stereochemistry of epi-zephyranthine was established.

Cycloadditions of 1-substituted 1,3-butadienes with 4- or 3-substituted 2(1H)-quinolones acting as dienophiles

Cycloadditions of 1,3-butadiene derivatives having an electron-rich group at the 1-position with 4- or 3-substituted 2(1H)-quinolones were carried out to give the richly functionalized phenanthridines under both atmospheric and high pressure conditions. Furthermore, the reactivity of 4- or 3-substituted 2(1H)-quinolones acting as a dienophile with 1-substituted dienes was examined using MO calculation.

Total synthesis and biological evaluation of Amaryllidaceae alkaloids: narciclasine, ent-7-deoxypancratistatin, regioisomer of 7-deoxypancratistatin, 10b-epi-deoxypancratistatin, and truncated derivatives

Biocatalytic approaches have yielded efficient total syntheses of the major Amaryllidaceae alkaloids, all based on the key enzymatic dioxygenation of suitable aromatic precursors. This paper discusses the logic of general synthetic design for lycoricidine, narciclasine, pancratistatin, and 7-deoxypancratistatin. Experimental details are provided for the recently accomplished syntheses of narciclasine, ent-7-deoxypancratistatin, and 10b-epi-deoxypancratistatin via a new and selective opening of a cyclic sulfate over aziridines followed by aza-Payne rearrangement. The structural core of 7-deoxypancratistatin has also been degraded to a series of intermediates in which the amino inositol unit is cleaved and deoxygenated in a homologous fashion. These truncated derivatives and the compounds from the synthesis of the unnatural derivatives have been tested against six important human cancer cell lines in an effort to further develop the understanding of the mode of action for the most active congener in this group, pancratistatin. The results of the biological activity testing as well as experimental, spectral, and analytical data are provided in this manuscript for all relevant compounds.

A short synthesis of (+)-narciclasine via a strategy derived from stereocontrolled epoxide formation and SnCl(4)-catalyzed arene-epoxide coupling

A facile construction of the typical framework of narcissus alkaloids has been realized by virtue of the development of a practical route involving stereocontrolled epoxide formation and SnCl(4)-catalyzed arene-epoxide coupling. To achieve this goal, it proved to be necessary to devise a strategy that would enable chemical transformations to install an epoxy moiety in a congested environment. The successful preparation of a hindered epoxide from O-isopropylidene-protected 4-aminocyclohexenol required three steps consisting principally of controlled bromohydration and base-promoted closure and N-alkylation. It was found that a catalytic amount of SnCl(4) not only maintained the catalytic cycle but also effected clean arylation to form a fused BC ring system. Several tactics that ultimately proved to be unsatisfactory are also discussed in an effort to set important boundary limits on arene-epoxide coupling. The requisite enantiopure 4-aminocyclohexenol was available via an asymmetric cycloaddition of diene to camphor-based chloronitroso. The total synthesis of (+)-narciclasine was realized in nine steps with an overall yield of 19%.

Diels-Alder cycloadditions of 2(1H)-quinolones having an electron-withdrawing group at the 3-position acting as dienophiles with dienes

Diels-Alder cycloadditions of 2(1H)-quinolones having an electron-withdrawing group at the 3-position with alkyl- and silyloxy-1,3-butadienes (2a,b) were carried out to give phenanthridones richly functionalized regio- or stereoselectively under conditions of atmospheric and high pressure. Furthermore, regioselectivity and chemoselectivity of 3-substituted 2(1H)-quinolones to 2a, b were examined using MO calculation.

Diels-Alder reaction of 1,3-butadiene derivatives with 1-methyl-2(1H)-quinolones having an electron-withdrawing group at the 4-position

Diels-Alder reactions of 1-methyl-2(1H)-quinolones having an electron-withdrawing group at the 4-position with isoprene, butadiene sulfone, and cyclohexadiene were performed to yield functionalized phenanthridones stereoselectively at atmospheric and at high pressure. Regioselectivity and stereochemistry of a methoxycarbonyl group were studied using the semi-empirical and ab initio MO methods, respectively.

Synthesis of phenanthridones using Diels-Alder reactions of 4-substituted 2(1H)-quinolones acting as dienophiles

Diels-Alder reactions of 2(1H)-quinolones having an electron-withdrawing group at the 4-position with 1,3-butadiene derivatives were carried out to give the phenanthridones richly functionalized under the conditions of atmospheric and high pressure. Furthermore, the reactivities of 4-substituted 2(1H)-quinolones acting as a dienophile were examined using MO calculation.