No abstract

Podophyllotoxin and its related aryltetralin cyclolignans belong to a family of important products that exhibit various biological properties (e.g., cytotoxic, insecticidal, antifungal, antiviral, anti-inflammatory, neurotoxic, immunosuppressive, antirheumatic, antioxidative, antispasmogenic, and hypolipidemic activities). This Review provides a survey of podophyllotoxin and its analogues isolated from plants. In particular, recent developments in the elegant total chemical synthesis, structural modifications, biosynthesis, and biotransformation of podophyllotoxin and its analogues are summarized. Moreover, a deoxypodophyllotoxin-based chemosensor for selective detection of mercury ion is described. In addition to the most active podophyllotoxin derivatives in each series against human cancer cell lines and insect pests listed in the tables, the structure-activity relationships of podophyllotoxin derivatives as cytotoxic and insecticidal agents are also outlined. Future prospects and further developments in this area are covered at the end of the Review. We believe that this Review will provide necessary information for synthetic, medicinal, and pesticidal chemistry researchers who are interested in the chemistry and biology of podophyllotoxins.

In continuation of our program aimed at the discovery and development of natural-product-based insecticidal agents, we have prepared three series of novel 4α-(acyloxy)-2'(2',6')-(di)halogenopodophyllotoxin derivatives modified in the C and E rings of podophyllotoxin, which is a naturally occurring aryltetralin lignan isolated from the roots and rhizomes of Podophyllum hexandrum . Their structures were well characterized by (1)H NMR, HRMS, ESI-MS, optical rotation, and mp. The stereochemical configurations of compounds 5s, 6b, 6d, and 7q were unambiguously confirmed by single-crystal X-ray diffraction. Their insecticidal activity was evaluated against the pre-third-instar larvae of oriental armyworm, Mythimna separata Walker, in vivo at a concentration of 1 mg/mL. These derivatives likely displayed the antimolting hormone effect. Among all the derivatives, especially compounds 5a, 5n, 7f, 7n, and 7w exhibited the most potent insecticidal activity with final mortality rates of 70% or so. This suggested that a chlorine or bromine atom introduced at the C2' or C2' and C6' positions on the E ring of podophyllotoxin was necessary for obtaining the potent compounds. This will pave the way for further design, structural modification, and development of podophyllotoxin derivatives as insecticidal agents.

In continuation of our program aimed at the discovery and development of natural-product-based pesticidal agents, 54 novel N-arylsulfonyl-3-acylindole arylcarbonyl hydrazone derivatives were prepared, and their structures were well characterized by ¹H NMR, ¹³C NMR, HRMS, ESI-MS, and mp. Their nematicidal activity was evaluated against that of the pine wood nematode, Bursaphelenchus xylophilus in vivo. Among all of the derivatives, especially V-12 and V-39 displayed the best promising nematicidal activity with LC₅₀ values of 1.0969 and 1.2632 mg/L, respectively. This suggested that introduction of R¹ and R² together as the electron-withdrawing substituents, R³ as the methyl group, and R⁴ as the phenyl with the electron-donating substituents could be taken into account for further preparation of these kinds of compounds as nematicidal agents. Six selected descriptors are a WHIM descriptor (E1m), two GETAWAY descriptors (R1m+ and R3m+), a Burden eigenvalues descriptor (BEHm8), and two edge-adjacency index descriptors (EEig05x and EEig13d). Quantitative structure-activity relationship (QSAR) studies demonstrated that the structural factors, such as molecular mass (a negative correlation with the bioactivity) and molecular polarity (a positive correlation with bioactivity), are likely to govern the nematicidal activities of these compounds. For this model, the correlation coefficient (R²(training set)), the leave-one-out cross-validation correlation coefficient (Q²(LOO)), and the 7-fold cross-validation correlation coefficient (Q²(7-fold)) were 0.791, 0.701, and 0.715, respectively. The external cross-validation correlation coefficient (Q²ext) and the root-mean-square error for the test set (RMSE(test set)) were 0.774 and 3.412, respectively. This study will pave the way for future design, structural modification, and development of indole derivatives as nematicidal agents.