Structural modification of tanshinone IIA and their α-glucosidase inhibitory activity.

α-Glucosidase is one of the therapeutic approaches for treating type 2 diabetes mellitus. Almost 95 % of diabetes patients worldwide have been diagnosed with type 2 diabetes, resulting in 1.5 million fatalities each year. Newly synthesized oxazole-based tanshinone IIA derivatives (1a-n) were designed and evaluated for their inhibitory activity against α-glucosidase enzyme. Eight compounds (1a-d, 1f-g, 1j, and 1m) demonstrated excellent inhibition with IC50 values ranging from 0.73 ± 0.11 to 9.46 ± 0.57 µM as compared to tanshinone IIA (IC50 = 11.39 ± 0.77 µM) and standard acarbose (IC50 = 100.00 ± 0.95 µM). Among this series, 1j bearing two hydroxyls group over the phenyl ring was identified as the most potent α-glucosidase inhibitor with IC50 value of 0.73 ± 0.11 µM. Molecular docking simulations were done for the most active compound to identify important binding modes responsible for inhibition activity of α-glucosidase. In addition, the kinetic study was also performed to understand the mode of inhibition.

Photocatalytic Tandem Radical Cyclization Enables Expeditious Total Synthesis of Epoxyhinokiol Analogues for Anticancer Activity Evaluation.

A photocatalytic radical cascade with an unusual endo-trig cyclization was developed, which enables the efficient assembly of divergent tricyclic diterpenoid frameworks. The first total synthesis of abietane 10-epi-epoxyhinoliol was thus achieved in six steps by a subsequent reductive coupling of i-PrBr under photoredox/nickel dual catalysis. Inhibitory tests of chiral 10-epi-epoxyhinoliol and its analogues in 4T1 cancer cells demonstrated the critical role of the C12 hydroxyl group, leading to a discovery of the simplified analogue with better activity.

Discovery and Bioinspired Synthesis of Salpratone A.

Salpratone A (1), a novel abietane diterpenoid containing a unique cis-fused A/B ring, was isolated from Salvia prattii. Bioactivity studies showed that 1 has potent activity in inhibiting platelet aggregation induced by multiple agonists as well as antithrombotic efficacy in the FeCl3-induced rat in vivo thrombosis model. Furthermore, a bioinspired synthesis of 1 from the abundant natural product ferruginol was achieved in 6 steps with a 22% overall yield. The key steps include a stereoselective allyl oxidation and a subsequent regioselective Meinwald rearrangement.

Design, synthesis, and evaluation of proliferation inhibitory activity of novel L-shaped ortho-quinone analogs as anticancer agents.

In this study, we present the design and synthesis of novel fully synthetic L-shaped ortho-quinone analogs with tanshinone IIA as the lead compoud, which is a molecule with numerous pharmacological benefits and potential to treat life-threatening diseases, such as cancer and viral infections. 24 L-shaped ortho-quinone analogs were designed and synthesized via click chemistry and introduced 1,2,3-triazole at the C-2 terminal of the furan ring. The cytotoxicity of these analogs toward different cancer cell lines was investigated in vitro. The new TD compounds showed potent inhibitory activities toward prostate cancer (PC3), leukemia (K562), breast cancer (MDA-231), lung cancer (A549), and cervical cancer (Hela) cell lines. Among them, TD1, TD11, and TD17 showed excellent broad-spectrum cytotoxic effects on five cancer cell lines by inducing apoptosis and arresting the cell cycle phase. Besides, TD1, TD11, and TD17 could target-bind with NQO1 protein in the prostate cancer cells PC3 leukemia cells K562. The results showed that removing the methyl group at C-3 and introducing 1,2,3-triazoles at the C-2 terminal of the furan ring were effective strategies for improving the broad-spectrum anticancer activity of L-shaped ortho-quinone analogs.

Design, synthesis and biological evaluation of tanshinone IIA-based analogues: Potent inhibitors of microtubule formation and angiogenesis.

We report the structural optimization of tanshinone IIA, a natural product which possesses anti-tumor properties but low water-solubility, weak antiproliferative activity and poor PK properties. A new series of ring A/C/D modified tanshinone analogues were synthesized and studied for their antiproliferative capacities against six human cancer cell lines. SAR study revealed that ring A cleavage of tanshinone IIA led to improved anti-cancer activity. Introduction of a methoxy group to the phenyl ring could enhance the anti-cancer activity even further. Compound 2f with methoxy group at C-8 position was selected as an early lead with IC50 values of 0.28-3.16 µM against six tested cell lines. 2f could bind to tubulin colchicine site, inhibit tubulin assembly and disrupt the normal formation of microtubule networks. Cellular mechanistic studies revealed that 2f induced apoptotic cell death of A549 cells in a dose-dependent manner. In vitro investigations showed that 2f impeded the tubule-formation of HUVECs and potently inhibited the proliferation, migration and invasion of A549 cells as well as HUVECs. Furthermore, the in vivo anti-angiogenic effect of 2f was confirmed via a zebrafish model test. The satisfactory physicochemical property and metabolic stability of 2f, as well as improved water-solubility, further suggested that 2f could serve as a promising tubulin inhibitor and anti-angiogenic agent.

Tanshinones and their Derivatives: Heterocyclic Ring-Fused Diterpenes of Biological Interest.

The available scientific literature regarding tanshinones is very abundant, and after its review, it is noticeable that most of the articles focus on the properties of tanshinone I, cryptotanshinone, tanshinone IIA, sodium tanshinone IIA sulfonate and the dried root extract of Salvia miltiorrhiza (Tan- Shen). However, although these products have demonstrated important biological properties in both in vitro and in vivo models, their poor solubility and bioavailability have limited their clinical applications. For these reasons, many studies have focused on the search for new pharmaceutical formulations for tanshinones, as well as the synthesis of new derivatives that improve their biological properties. To provide new insights into the critical path ahead, we systemically reviewed the most recent advances (reported since 2015) on tanshinones in scientific databases (PubMed, Web of Science, Medline, Scopus, and Clinical Trials). With a broader perspective, we offer an update on the last five years of new research on these quinones, focusing on their synthesis, biological activity on noncommunicable diseases and drug delivery systems, to support future research on its clinical applications.

Selective stabilization of multiple promoter G-quadruplex DNA by using 2-phenyl-1H-imidazole-based tanshinone IIA derivatives and their potential suppressing function in the metastatic breast cancer.

The G-quadruplex (G4) DNA, which has been developed as a potential anticancer target in drug screening and design, plays a crucial role in the oncogene transcription and translation. Tanshinone IIA derivatives with a planar heterocycle structure may function as G4 stabilizers. We present an innovative case of imidazole-based tanshinone IIA derivatives (1-8) especially compound 4 that improve the selectivity and the binding affinity with G4 DNA and enhance the target tumor inhibition. Cellular and in vivo experiments indicate that the tanshinone IIA derivative 4 inhibits the growth, metastasis, and angiogenesis of triple-negative breast cancer cells possibly through the stabilization of multiple G4 DNAs (e.g., c-myc, K-ras, and VEGF) to induce DNA damage. Further investigation of the intermolecular interaction and the molecular docking indicates that tanshinone IIA derivatives have better selective binding capability to various G4 DNAs than to double-stranded DNA. These findings provide guidance in modifying the molecular structures of tanshinone IIA derivatives and reveal their potential to function as specific G4 stabilizers.

Evaluation of the anti-inflammatory effects of synthesised tanshinone I and isotanshinone I analogues in zebrafish.

During inflammation, dysregulated neutrophil behaviour can play a major role in a range of chronic inflammatory diseases, for many of which current treatments are generally ineffective. Recently, specific naturally occurring tanshinones have shown promising anti-inflammatory effects by targeting neutrophils in vivo, yet such tanshinones, and moreover, their isomeric isotanshinone counterparts, are still a largely underexplored class of compounds, both in terms of synthesis and biological effects. To explore the anti-inflammatory effects of isotanshinones, and the tanshinones more generally, a series of substituted tanshinone and isotanshinone analogues was synthesised, alongside other structurally similar molecules. Evaluation of these using a transgenic zebrafish model of neutrophilic inflammation revealed differential anti-inflammatory profiles in vivo, with a number of compounds exhibiting promising effects. Several compounds reduce initial neutrophil recruitment and/or promote resolution of neutrophilic inflammation, of which two also result in increased apoptosis of human neutrophils. In particular, the methoxy-substituted tanshinone 39 specifically accelerates resolution of inflammation without affecting the recruitment of neutrophils to inflammatory sites, making this a particularly attractive candidate for potential pro-resolution therapeutics, as well as a possible lead for future development of functionalised tanshinones as molecular tools and/or chemical probes. The structurally related ß-lapachones promote neutrophil recruitment but do not affect resolution. We also observed notable differences in toxicity profiles between compound classes. Overall, we provide new insights into the in vivo anti-inflammatory activities of several novel tanshinones, isotanshinones, and structurally related compounds.

Functional Integration of Two CYP450 Genes Involved in Biosynthesis of Tanshinones for Improved Diterpenoid Production by Synthetic Biology.

Cytochrome P450s (CYPs) are important enzymes in the secondary metabolism of plants and have been recognized as key players in bioengineering and synthetic biology. Previously reported CYP76AH1 and CYP76AH3, having greater than 80% sequence homology, played a continuous catalytic role in the biosynthesis of tanshinones in Salvia miltiorrhiza. Homology modeling indicates that four sites might be responsible for differences in catalytic activity between the two enzymes. A series of modeling-based mutational variants of CYP76AH1 were designed to integrate the functions of the two CYPs. The mutant CYP76AH1D301E,V479F, which integrated the functions of CYP76AH1 and CYP76AH3, was found to efficiently catalyze C11 and C12 hydroxylation and C7 oxidation of miltiradiene substrates. Integration and utilization of CYP76AH1D301E,V479F by synthetic biology methods allowed the robust production of 11-hydroxy ferruginol, sugiol, and 11-hydroxy sugiol in yeast. The functionally integrated CYP gene after active site modifications improves catalytic efficiency by reducing the transfer of intermediate metabolites between component proteins. This provides a synthetic biology reference for improving the catalytic efficiencies of systems that produce plant natural products in microorganisms.

Synthesis and anticancer evaluation of novel 1H-benzo[d]imidazole derivatives of dehydroabietic acid as PI3Kα inhibitors.

Phosphatidylinositol 3-kinase (PI3K) is one of the most attractive therapeutic targets for cancer treatment. In this study, a series of new 2-arylthio- and 2-arylamino-1H-benzo[d]imidazole derivatives of dehydroabietic acid were designed, synthesized and characterized by 1H NMR, 13C NMR, IR and MS spectra analyses. In the in vitro anticancer assay, some title compounds showed significant inhibitory activities against four cancer cell lines (HCT-116, MCF-7, HeLa and HepG2). Among them, compound 9g exhibited the most potent activity with IC50 values of 0.18 ± 0.03, 0.43 ± 0.05, 0.71 ± 0.08 and 0.63 ± 0.09 µM against four cancer cell lines, and considerably lower cytotoxicity to human gastric mucosal cell line Ges-1 (IC50: 21.95 ± 0.73 µM). Besides, compound 9g displayed a certain selective activity to PI3Kα (IC50 = 0.012 ± 0.002 µM) over PI3Kß, γ and δ, and meanwhile, it can remarkably decrease the expression level of p-Akt (Ser473). In addition, compound 9g could increase intracellular reactive oxygen species level, decrease mitochondrial membrane potential, upregulate Bax and cleaved caspase-3/9 levels, downregulate Bcl-2 level and thus induce the apoptosis of HCT-116 cells in a dose-dependent manner. The results suggested that compound 9g could be considered as a promising PI3Kα inhibitor.

Synthesis and structure-activity relationships of novel abietane diterpenoids with activity against Staphylococcus aureus.

Aim: To find alternative compounds against methicillin-resistant Staphylococcus aureus (MRSA) and methicillin-susceptible S. aureus (MSSA), novel derivatives from dehydroabietic acid were synthesized. Methods & results: Compound 12 was the most effective against 15 MRSA and 11 MSSA with minimum inhibitory concentration values ranging from 3.9 to 15.6 µg/ml. Although less active than 12, compound 11, followed by 25 and 13, also exhibited anti-staphylococcal activity. Additional studies showed that compound 12 is devoid of toxic effect on non-target cells. A structure-activity relationship study revealed that an oxime at C-13 together with a hydroxyl at C-12 could play a key role in the activity. Conclusion: These structures, in particular compound 12, could arise as templates for the development of agents against MRSA and MSSA.

Synthesis and Antiproliferative Evaluation of Novel Hybrids of Dehydroabietic Acid Bearing 1,2,3-Triazole Moiety.

To discover novel potent cytotoxic diterpenoids, a series of hybrids of dehydroabietic acid containing 1,2,3-triazole moiety were designed and synthesized. The target compounds were characterized by means of FT-IR, 1H NMR, 13C NMR, ESI-MS and elemental analysis techniques. The in vitro cytotoxicity of these compounds was evaluated by standard MTT (methyl thiazolytetrazolium) assay against CNE-2 (nasopharynx), HepG2 (liver), HeLa (epithelial cervical), BEL-7402 (liver) human carcinoma cell lines and human normal liver cell (HL-7702). The screening results revealed that most of the hybrids showed significantly improved cytotoxicity over parent compound DHAA. Among them, [1-(3-fluorobenzyl)-1H-1,2,3-triazole-4-yl]dehydroabietic acid methyl ester (3c), and [1-(2-nitrobenzyl)-1H-1,2,3-triazole-4-yl]dehydroabietic acid methyl ester (3k) displayed better antiproliferative activity with IC50 (50% inhibitory concentration) values of 5.90 ± 0.41 and 6.25 ± 0.37 µM toward HepG2 cells compared to cisplatin, while they exhibited lower cytotoxicity against HL-7702. Therefore, the 1,2,3-triazole-hybrids could be a promising strategy for the synthesis of antitumor diterpenoids and it also proved the essential role of 1,2,3-triazole moiety of DHAA in the biological activity.

Synthesis and biological evaluation of novel N-(piperazin-1-yl)alkyl-1H-dibenzo[a,c]carbazole derivatives of dehydroabietic acid as potential MEK inhibitors.

In this paper, a series of novel 1H-dibenzo[a,c]carbazole derivatives of dehydroabietic acid bearing different N-(piperazin-1-yl)alkyl side chains were designed, synthesised and evaluated for their in vitro anticancer activities against three human hepatocarcinoma cell lines (SMMC-7721, HepG2 and Hep3B). Among them, compound 10g exhibited the most potent activity against three cancer cell lines with IC50 values of 1.39 ± 0.13, 0.51 ± 0.09 and 0.73 ± 0.08 µM, respectively. In the kinase inhibition assay, compound 10g could significantly inhibit MEK1 kinase activity with IC50 of 0.11 ± 0.02 µM, which was confirmed by western blot analysis and molecular docking study. In addition, compound 10g could elevate the intracellular ROS levels, decrease mitochondrial membrane potential, destroy the cell membrane integrity, and finally lead to the oncosis and apoptosis of HepG2 cells. Therefore, compound 10g could be a potent MEK inhibitor and a promising anticancer agent worthy of further investigations.

Synthesis of novel tanshinone derivatives for treatment of castration-resistant prostate cancer.

Prostate cancer is the second leading cause of death in USA and has developed serious resistance to current drugs. Thus, development of new drugs for the treatment of castration-resistant prostate cancer (CRPC) is urgently needed. In this study, 25 novel derivatives of tanshinone IIA as potential androgen receptor (AR) suppression reagents for the treatment of CRPC have been synthesized. The inhibition on DHT-mediated AR transactivation and cell viability assay were performed to test the synthesized compounds. The results showed that among 25 new compounds, seven methoxy-substituted tanshinone IIA derivatives showed significant inhibition effect on DHT-mediated AR transactivation. In particular, TAN-24 that contains three methoxy groups showed the strongest inhibition effect on DHT-mediated AR transactivation. In addition, TAN-24 also suppressed DHT-AR transactivation more effectively than those of tanshinoneIIA and enzalutamide. In cytotoxicity against human prostate cancer cell lines assay, TAN-24 exhibited the most potent in vitro cytotoxicity against LNCaP and CWR22Rv1 cells, with IC50 values 20- and 19-times lower than those of tanshinone IIA and comparable to enzalutamide. TAN-24 reported in the present work represents a novel and effective AR suppression drug, showing great potential for the treatment of CRPC.

Synthesis of New Dihydroquinopimaric Acid Analogs with Nitrile Groups as Apoptosis-Inducing Anticancer Agents.

BACKGROUND: Cyan-containing compounds are of great interest as potential anticancer agents. Terpenoids can severe as a natural matrix for the development of promising derivatives with antitumor activity. METHODS: The 2-cyanoethoxy methyl dihydroquinopimarate derivatives (5-9) were synthesized by the reaction of the intermediates (1-4) with acrylonitrile in the presence of alkali (30% KOH solution) using triethylbenzylammonium chloride. The cytotoxicity evaluation was carried out according to the National Cancer Institute (NCI) Protocol, while apoptosis was studied by flow cytometric analysis of Annexin V and 7-aminoactinomycin D staining and cell cycle was analyzed using the method of propidium iodide staining. RESULTS: Synthesis of new dihydroquinopimaric acid derivatives with nitrile groups was carried out. The obtained cyanoethyl derivatives were converted into tetrazole, amine, oxadiazole and amidoxime analogs. The primary screening for antitumor activity showed the highest cytotoxic potency of the cyanoethyl-substituted compounds. The introduction of cyanoethyl groups at C-1, C-4 and C-1, C-4, C-20 positions of dihydroquinopimaric acid methyl ester provided antiproliferative effect towards the Jurkat, K562, U937, and HeLa tumor cell cultures (CC50=0.045-0.154µM). These nitrile derivatives are effective inducers of tumor cell apoptosis affecting the S and G2 phases of the cell cycle in a dose-dependent manner. CONCLUSION: The cyanoethyl analogs of dihydroquinopimaric acid reported herein are apoptosis inducers and cytotoxic agents. These findings will be useful for the further design of more potent cytotoxic agents based on natural terpenes.

Semisynthesis of epoxy-pimarane diterpenoids from kirenol and their FXa inhibition activities.

Kirenol is one of the biologically active diterpenoids from Siegesbeckia pubescens. In terms of the high content and typical structure, many ent-diterpenoids separated from S. pubescens were presumed to be biologically related to kirenol. Among them, epoxy-pimarane diterpenoids are belonging to a special family of naturally occurring compounds that attracted our attentions on their putative biosynthesis pathway and biological activities. Here, we designed and synthesized two known 14,16-epoxy-pimarane diterpenoids (2 and 3) and five 8,15-epoxy-pimarane diterpenoids (4-8) from kirenol. Their absolute structures were determined by 1D and 2D NMR data and the absolute configurations of 4 were confirmed by X-ray crystallographic data. Their inhibition effects on factor Xa (FXa) were evaluated to assess the potentiality of epoxy-pimarane diterpenoids as FXa inhibitor agents.

Synthesis of 4- epi-Parviflorons A, C, and E: Structure-Activity Relationship Study of Antiproliferative Abietane Derivatives.

The first syntheses of 4- epi-parviflorons A, C, and E (4- epi-1-3) were achieved in 12-13 steps from commercially available (-)-abietic acid (5). All synthesized compounds, including intermediates and derivatives, were evaluated for antiproliferative activity against five human tumor cell lines. A structure-activity relationship study revealed no significant difference between Pf E and 4- epi-Pf E, the importance of two oxygen functional groups at C-11 and C-12 for antiproliferative activity, as well as a combination of carbomethoxy at C-4 and a benzoyl ester with electron-drawing group at C-12 or hydroxymethyl at C-4 and an appropriate oxidation state of ring-B/C for triple-negative breast cancer cell selectivity.

Carnosic Acid, Tangeretin, and Ginkgolide-B Anti-neoplastic Cytotoxicity in Dual Combination with Dexamethasone-[anti-EGFR] in Pulmonary Adenocarcinoma (A549).

BACKGROUND: Traditional chemotherapeutics of low-molecular weight diffuse passively across intact membrane structures of normal healthy cells found in tissues and organ systems in a non-specific unrestricted manner which largely accounts for the induction of most sequelae which restrict dosage, administration frequency, and duration of therapeutic intervention. Molecular strategies that offer enhanced levels of potency, greater efficacy and broader margins-of-safety include the discovery of alternative candidate therapeutics and development of methodologies capable of mediating properties of selective "targeted" delivery. MATERIALS AND METHODS: The covalent immunopharmaceutical, dexamethasone-(C21-phosphoramidate)-[anti- EGFR] was synthesized utilizing organic chemistry reactions that comprised a multi-stage synthesis regimen. Multiple forms of analysis were implemented to vadliate the successful synthesis (UV spectrophotometric absorbance), purity and molar-incorporation-index (UV spectrophotometric absorbance, chemical-based protein determination), absence of fragmentation/polymerization (SDS-PAGE/chemiluminescent autoradiography), retained selective binding-avidity of IgG-immunoglobulin (cell-ELISA); and selectively "targeted" antineoplastic cytotoxicity (biochemistry-based cell vitality/viability assay). RESULTS: The botanicals carnosic acid, ginkgolide-B and tangeretin, each individually exerted maximum antineoplastic cytotoxicity levels of 58.1%, 5.3%, and 41.1% respectively against pulmonary adenocarcinoma (A549) populations. Dexamethasone-(C21-phosphoramidate)-[anti-EGFR] formulated at corticosteroid/ glucocorticoid equivalent concentrations produced anti-neoplastic cytotoxicity at levels of 7.7% (10-9 M), 26.9% (10-8 M), 64.9% (10-7 M), 69.9% (10-6 M) and 73.0% (10-5 M). Ccarnosic acid, ginkgolide-B and tangeretin in simultaneous dual-combination with dexamethasone-(C21-phosphoramidate)-[anti-EGFR] exerted maximum anti-neoplastic cytotoxicity levels of 70.5%, 58.6%, and 69.7% respectively. DISCUSSION: Carnosic acid, ginkgolide-B and tangeretin botanicals exerted anti-neoplastic cytotoxicity against pulmonary adenocarcinoma (A549) which additively contributed to the anti-neoplastic cytotoxic potency of the covalent immunopharmaceutical, dexamethasone-(C21-phosphoramidate)-[anti-EGFR]. Carnosic acid and tangeretin were most potent in this regard both individually and in dual-combination with dexamethasone-(C21- phosphoramidate)-[anti-EGFR]. Advantages and attributes of carnosic acid and tangeretin as potential monotherapeutics are a wider margin-of-safety of conventional chemotherapeutics which would readily complement the selective "targeted" delivery properties of dexamethasone-(C21-phosphoramidate)-[anti-EGFR] and possibly other covalent immunopharmaceuticals in addition to providing opportunities for the discovery of combination therapies that provide heightened levels of anti-neoplastic efficacy.

Synthesis of Myrocin G, the Putative Active Form of the Myrocin Antitumor Antibiotics.

The antiproliferative antimicrobial fungal metabolites known as the myrocins have been proposed to cross-link DNA by double nucleotide addition. However, the nature of the DNA-reactive species is ambiguous, as myrocins have been isolated as functionally distinct 5-hydroxy-γ-lactone and diosphenol isomers. Based on literature precedent, we hypothesized that the diosphenol 7 (assigned here the trivial name myrocin G) is the biologically active form of the representative isolate (+)-myrocin C (1). To probe this, we developed a short enantioselective route to 7. A powerful fragment-coupling reaction that forms the central ring of the target in 38% yield and in a single step was developed. In support of our hypothesis, 7 was efficiently transformed to the bis(sulfide) 6, a product previously isolated from reactions of 1 with excess benzenethiol. This work provides the first direct access to the diosphenol 7, sets the stage for elucidating the mode of interaction of the myrocins with DNA, and provides a foundation for the synthesis of other pimarane diterpenes.

Ugi multicomponent-reaction: Syntheses of cytotoxic dehydroabietylamine derivatives.

Isocyanide-based multicomponent reactions - especially the standard four component Ugi reaction - provide an easy and powerful access to compounds with an auspicious pharmacological potential. Therefore, a set of 16 novel derivatives of the diterpene dehydroabietylamine was synthesized by the Ugi-4CR. The subsequent screening of the synthesized α-acylamino carboxamides in colorimetric sulforhodamine B assays revealed an in vitro cytotoxicity towards several human tumor cell lines. Particularly, the rhodamine B conjugates 14-16 showed a remarkable cytotoxic activity, characterized by EC50 values in a low three-digit nanomolar range. The screening of rhodamine B amide 17 that was obtained for comparison by a Schotten-Baumann reaction showed that the linkage of the rhodamine B moiety and the diterpene influences significantly its cytotoxic potency. While 14 was highly cytotoxic and acted as a mitocan, compound 17 was not cytotoxic at all. This observation underlines the importance of the type of coupling between the diterpene and the rhodamine part. The presence of a rhodamine B moiety in the molecules doesn't necessarily guarantee that the compound is cytotoxic.