4-Aza-2,3-dehydro-4-deoxypodophyllotoxins: simple aza-podophyllotoxin analogues possessing potent cytotoxicity

4-Aza-2,3-dehydro-4-deoxypodophyllotoxin analogues 3a-n were synthesized through quinolines 2a-n. Comparison of their cytotoxicity against P-388 leukemia cells revealed that the steric effects of the ring B substituents on the activity are greater than the electronic effects, while the presence of a methoxy group on the ring E is not essential to exhibit potent cytotoxicity. Analogues 3a and 3b proved to be more than twice as cytotoxic as natural podophyllotoxin (1).     

Synthesis of 4beta-amido and 4beta-sulphonamido analogues of podophyllotoxin as potential antitumour agents

The new 4beta-amido analogues of podophyllotoxin or 4'-O-demethylepipodophyllotoxin have been prepared either by the coupling of 4beta-amino podophyllotoxin or 4beta-amino-4'-O-demethyl epipodophyllotoxin with the corresponding acids in presence of DCC in dichloromethane or by treating the appropriate acid chloride or sulphonyl chloride in presence of Et(3)N. These 4beta-amido and 4beta-sulphonamido derivatives of podophyllotoxin have been evaluated for their cytotoxicity against six human cancer cell lines. Some of these analogues have shown promising anticancer activity.     

Synthesis and evaluation of the cell cycle arrest and CT DNA interaction properties of 4β-amino-4′-O-demethyl-4-deoxypodophyllotoxins

A series of 4β-amino-4′-O-demethyl-4-deoxypodophyllotoxin derivatives were synthesized, and their cytotoxicities against several human cancer cell lines, including HepG2, A549, HeLa and HCT-8 cells, evaluated. Some of these compounds exhibited higher levels of cytotoxicity than the anticancer drug etoposide. 4β-N-(4-Nitrophenyl piperazinyl)-4′-O-demethyl-4-deoxypodophyllotoxin (11) was found to be the most potent synthesized compound in the current study, and induced cell cycle arrest in the G2/M phase in HeLa cells, which was accompanied by apoptosis. Furthermore, this compound activated the expression of cdc2, cyclin B1, p53 and caspase-3 in HeLa cells, leading to changes in the conformation of calf thymus DNA from the B-form to a more compact C-form.     

Natural products-based insecticidal agents 5. Design,semisynthesis and insecticidal activity of novel 4′-substituted benzenesulfonate derivatives of 4-deoxypodophyllotoxin against Mythimna separata Walker in vivo

In an attempt to find the effective phytopesticides, eight novel 4′-substituted benzenesulfonate derivatives of 4-deoxypodophyllotoxin were synthesized and preliminarily tested against the pre-third-instar larvae of Mythimna separata Walker in vivo at the concentration of 1 mg/mL. Among all of the tested analogs, compounds 5a, 5c, 5d, and 5h showed the higher insecticidal activity than 4-deoxypodophyllotoxin. Especially 5a exhibited the most potent insecticidal activity compared with toosendanin, a commercial insecticide derived from Melia azedarach.     

Prodrugs of 4'-demethyl-4-deoxypodophyllotoxin: synthesis and evaluation of the antitumor activity

A series of prodrugs of 4'-demethyl-4-deoxypodophyllotoxin (DDPT) including carbamates (3-8), a carbonate (9) and water-soluble amino acid derivatives (10-17) were prepared and tested for their antitumor activity. The carbamate 6 (2-hydroxyethylcarbamoyl-DDPT), carbonate 9 (2-chloroethyloxycarbonyl-DDPT), and most of amino acid prodrugs (12-17) showed enhanced antitumor activity.     

Insight into dihalogenation of E-ring of podophyllotoxins,and their acyloxyation derivatives at the C4 position as insecticidal agents

Unexpected sequential E-ring dihalogenation of podophyllotoxin analogues is reported. It demonstrated that a chlorine/bromine atom was prior introduced at the C2′ position of podophyllotoxin, and the corresponding free rotation of E-ring around the C1–C1′ bond of 2′-chloro or 2′-bromopodophyllotoxin was restricted. When 2′-chloro or 2′-bromopodophyllotoxin reacted with N-chlorosuccinimide (NCS), the chlorine atom was regioselectively introduced at their C6′ position on the E-ring. Whereas 2′-chloro or 2′-bromopodophyllotoxin reacted with NBS, the bromine atom was regioselectively introduced at their C5 position on the B-ring. When 2′-chloropodophyllotoxin reacted with different carboxylic acids in the presence of BF₃·Et₂O, the steric effect of its E-ring for stereoselective synthesis of 4β-acyloxy-2′-chloropodophyllotoxin derivatives was observed. The insecticidal activity of 2′(2′,6′)-(di)halogen-substituted podophyllotoxin derivatives were evaluated with Mythimna separata Walker.     

Biosynthesis of Podophyllum lignans—II. Interconversions of aryltetralin lignans in Podophyllum hexandrum

Feeding experiments in Podophyllum hexandrum plants with labelled aryltetralin lignans have established much of the biosynthetic interrelationships existing amongst Podophyllum lignans. Thus, desoxypodophyllotoxin is converted into podophyllotoxin, which in turn is oxidized to podophyllotoxone, although this latter step appears to be reversible. A similar sequence is proposed for the corresponding 4′-demethyl derivatives. Although 4′-demethyldesoxy-podophyllotoxin is readily converted into 4′-demethylpodophyllotoxin, neither compound is incorporated into lignans of the 4′-methyl series such as podophyllotoxin. The Podophyllum lignans may be subdivided biogenctically into two groups, those with 3,4,5-trimethoxy substitution in the pendent aryl ring, and those with a 4-hydroxy-3,5-dimethoxy substituted pendent ring, although these probably arise from a common precursor. A biogenetic scheme interrelating all of the known Podophyllum aryltetralin lignans is proposed.     

内生放线菌对鬼臼毒素的微生物转化

调查桃儿七根茎内生放线菌对鬼臼毒素的微生物转化,以期获得一些鬼臼毒素的结构类似物或衍生物。利用表面消毒法分离内生放线菌;采用薄层层析和高效液相色谱(HPLC)方法筛选转化鬼臼毒素的内生放线菌;利用硅胶柱层析和制备HPLC分离纯化生物转化产物;应用波谱技术解析转化产物的化学结构;通过形态学、生理生化特征和16S rRNA基因序列分析对内生放线菌进行初步鉴定。从桃儿七根茎中分离出20株内生放线菌,经筛选发现其中1株放线菌能转化鬼臼毒素,其产物为4’-去甲基表鬼臼毒素。初步鉴定该内生放线菌为Streptomyces sp.。内生放线菌Streptomyces sp.能对鬼臼毒素进行去甲基和异构化修饰,推测其可能具有O-去甲基化酶和异构化酶。     

Synthesis and spectral characteristics of some unusual fatty esters of podophyllotoxin

Five fatty ester derivatives of podophyllotoxin have been prepared by reacting the corresponding fatty acids with the hydroxy group of podophyllotoxin in the presence of dimethylaminopyridine and N,N-dicyclohexylcarbodiimide. The fatty acids incorporated are: 9,12-epoxy-9,11-octadecadienoic acid, octadec-11E-en-9-ynoic acid, 11,12-E-epoxy-octadec-9-ynoic acid, octadeca-9Z,11E-dienoic acid and 9,10-dibromooctadecanoic acid. The average yield of esterification was >95% and the structures of the products were confirmed by a combination of nuclear magnetic resonance spectroscopic and mass spectrometric analyses.     

Tumour-inhibitory aryltetralin lignans from Podophyllum pleianthum

Roots of Podophyllum pleianthum contain eight aryltetralin lignans: podophyllotoxin, desoxypodophyllotoxin, podophyllotoxone, isopicropodophyllone and the four corresponding 4′-demethyl derivatives. The lignan pattern is very similar to that of P. hexandrum. A useful TLC spray reagent for Podophyllum lignans is described.     

Synthesis and biological evaluation of novel 4β-(1,3,4-oxadiazole-2-amino)-podophyllotoxin derivatives

A series of new 4β-(1,3,4-oxadiazole-2-amino)-podophyllotoxin derivatives were designed and synthesized. Their cytotoxicity in vitro against six tumor cell lines (DU-145, SGC-7901, A549, SH-SY5Y, HepG2 and HeLa) were evaluated by standard MTT assay. The pharmacological results showed that most of the newly synthesized podophyllotoxin derivatives displayed potent cytotoxicity against at least one of the tested tumor cells; and among the new derivatives, 11b was more potent than podophyllotoxin against HepG2 and Hela cell lines. Furthermore, 11b exhibited much better selectivity toward the normal cell lines L929 and Vero than etoposide, 5-Fu and podophyllotoxin. The possible antitumor mechanism of 11b is to inhibit the activity of DNA topoisomerase II, result in the S-phase arrest, and then cause apoptotic cell death.     

Novel semisynthetic spin-labeled derivatives of podophyllotoxin with cytotoxic and antioxidative activity

A series of novel spin-labeled podophyllotoxin derivatives were synthesized by reacting the corresponding N-(1-oxyl-2,2,6,6-tetramethyl-4-piperidinyloxy carbonyl)-amino acids with 4β-amino-4′-demethylepipodophyllotoxin. The synthesized derivatives 12a–g were evaluated for the partition coefficients, cytotoxicities in vitro against three tumor cell lines (A-549, HL-60, and RPMI-8226) and antioxidative activities in tissues of SD rats by the TBA method. The vast majority of target compounds have shown superior or comparable activities against A-549, HL-60, and RPMI-8226 compared to VP-16, and they have shown more significant antioxidative activities and superior water solubility than VP-16.     

Synthesis and anti-HIV-1 activities of novel podophyllotoxin derivatives

In order to explore the range of biological activities of the podophyllotoxin compound class, a novel series of derivatives of podophyllotoxin, which were conjugates containing stavudine and different structural podophyllotoxin analogues, were designed, synthesized, and evaluated for their anti-HIV-1 activities in vitro. Among these compounds, 19d and 19c showed the highest anti-HIV-1 activities with EC(50) values of 0.17 and 0.29 microM and TI values of 466.9 and 354.5, respectively.     

9-Deoxopodophyllotoxin derivatives as anti-cancer agents.

Several 9-deoxo-9-substituted podophyllotoxin derivatives were synthesised starting from naturally occuring podophyllotoxin and their anti-cancer activity was evaluated against in vitro human cancer cell line assay. It was observed that these compounds do possess good anti-cancer activity particularly against ovarian, renal and lung cancer cell lines.     

Podophyllotoxin

Podophyllin, an ethanolic extract of Podophyllum peltatum L. or P. emodi Wall (syn. P. hexandnum Royle), is a good source of the aryltetralin-type lignan, podophyllotoxin. The latter compound, as well as its congeners and derivatives exhibit pronounced biological activity mainly as strong antiviral agents and as antineoplastic drugs. The podophyllotoxin derivatives etoposide, etopophos (etoposide phosphate), and teniposide are thus successfully utilized in the treatment of a variety of malignant conditions. Continued research on the Podophyllum lignans is currently focused on structure optimization to generate derivatives with superior pharmacological profiles and broader therapeutic scope, and the development of alternative and renewable sources of podophyllotoxin.     

Natural products-based insecticidal agents 6. Design,semisynthesis, and insecticidal activity of novel monomethyl phthalate derivatives of podophyllotoxin against Mythimna separata Walker in vivo

To discover the more potent analogs, 12 novel monomethyl phthalate derivatives of podophyllotoxin were synthesized and preliminarily tested against the pre-third-instar larvae of Mythimna separata Walker in vivo at the concentration of 1 mg/mL. Compounds 8e–i showed the higher insecticidal activity than podophyllotoxin. Especially 8g exhibited the most potent insecticidal activity compared with toosendanin, a commercially available insecticide derived from Melia azedarach. The structure–activity relationships demonstrated that trans-lactone, 4β-substitution, 2β-chlorine substitution, and 4′-methoxy group were the important structural properties of podophyllotoxins for good insecticidal activity.     

Anticancer drugs. II. Synthesis and biological evaluation of spin labeled derivatives of podophyllotoxin

The spin labeled derivatives of podophyllotoxin, 4-[4'-(2',2',6',6'-tetramethyl-l'-piperidinyloxy)amino] -4'-demethylepipodophyllotoxin(GP-7,3) and N-podophyllic acid-N'-[4-(2,2,6,6-tetramethyl-l-piperidinyloxy)] thiosemicarbazide(GP-4,5) were synthesized and tested for their anticancer activity against the mouse solid tumors S180 and HepA in vivo, and the mouse lymphocytic leukemia L1210 and human stomach carcinoma SGC-7901 cells in vitro. At equitoxic concentrations, the anticancer activity of GP-7(3) was found to be similar to that of the clinically used VP-16(2). The toxicity of GP-7(3) (LD50231.2 mg/Kg) is 3.3 times lower than that of VP-16 (LD50 69.5 mg/Kg). GP-7(3) exhibits low subchronic toxicity. The total chemical yield of GP-7 (26%) is 4 times higher than that of VP-16 (6%) (based on podophyllotoxin). Therefore, GP-7(3) seems to be a promising new entry into the podophyllotoxin class of anticancer drugs.     

Biotechnological interventions for harnessing podophyllotoxin from plant and fungal species: current status,challenges, and opportunities for its commercialization

Podophyllotoxin is an aryltetralin lignan synthesized in several plant species, which is used in chemotherapies for cancers and tumor treatment. More potent semisynthetic derivatives of podophyllotoxin such as etoposide and teniposide are being developed and evaluated for their efficacy. To meet the ever increasing pharmaceutical needs, species having podophyllotoxin are uprooted extensively leading to the endangered status of selective species mainly Sinopodophyllum hexandrum. This has necessitated bioprospection of podophyllotoxin from different plant species to escalate the strain on this endangered species. The conventional and non-conventional mode of propagation and bioprospection with the integration of biotechnological interventions could contribute to sustainable supply of podophyllotoxin from the available plant resources. This review article is focused on the understanding of different means of propagation, development of genomic information, and its implications for elucidating podophyllotoxin biosynthesis and metabolic engineering of pathways. In addition, various strategies for sustainable production of this valuable metabolite are also discussed, besides a critical evaluation of future challenges and opportunities for the commercialization of podophyllotoxin.     

Different strategies for the chemical synthesis of lignans

This paper summarises the results of three projects. The first is concerned with developing general routes for the synthesis of lignans. In particular, two routes involving tandem conjugate addition reactions and Diels Alder reactions respectively that have been used to synthesise podophyllotoxin derivatives are described. The second project is concerned with the asymmetric synthesis of lignans and involves the application of these reactions, with the introduction of a menthyloxy group as a chiral auxiliary, to achieve the asymmetric synthesis of podophyllotoxin derivatives. The third project is concerned with the attempted biomimetic syntheses of podophyllotoxin derivatives using oxidative coupling reactions. Attention is focussed primarily on the use of hypervalent iodine reagents, which yield stegane and isostegane derivatives rather than podophyllotoxin derivatives. Other examples of biaryl coupling leading to stegane and isostegane derivatives are included, and other examples of lignan synthesis involving hypervalent iodine reagents are also described. Abbreviations: DDQ – 2,3-dichloro-5,6-dicyano-1,4-benzoquinone; DMAD – dimethyl acetylenedicarboxylate (dimethyl butynedioate); PIDA – phenyliodonium diacetate, iodobenzene diacetate; PIFA – phenyliodonium bis(trifluoroacetate), [bis(trifluoroacetoxy) iodobenzene]; Ra-Ni – Raney nickel; TBAF – tetrabutylammonium fluoride; TBDMS –t-butyldimethylsilyl; TFA – trifluoroacetic acid; TFAA – trifluoroacetic anhydride; TFE – 2,2,2-trifluoroethanol; TTFA – thallium(III) trifluoroacetate.     

Chemoinduction of cytotoxic selectivity in Podophyllotoxin-related lignans

Lignans are widely distributed in the plant kingdom, and display a variety of biological activities which have attracted the attention of the scientific community for decades. Several representative compounds of the cyclolignan class, such as podophyllotoxin and its semisynthetic derivative, etoposide, are currently used for the clinical treatment of warts and malign neoplasms. Other cyclolignans are involved in antineoplastic and antiarthritic clinical trials. Numerous podophyllotoxin-related compounds have been prepared through modification of nearly all the positions on the cyclolignan skeleton in the search of new, more selective and less toxic anticancer drugs. Our group has been interested in the chemoinduction of drug selectivity for several years, and we have designed and prepared new podophyllotoxin derivatives by modification mainly on the C and D-rings of the podophyllotoxin skeleton. Those derivatives, bearing an electrophilic functionality at C-9, have shown, both in vitro and in vivo, a high degree of selectivity against colon carcinoma, and less cytotoxicity for other neoplastic systems and normal kidney fibroblasts. The main structural modifications found in the literature for the podophyllotoxin skeleton in the past decade, including those from our research group, are presented in this article.