The reactivity of drimane unsaturated dialdehydes towards nucleophiles

Anticancer Activity of Natural and Semi-Synthetic Drimane and Coloratane Sesquiterpenoids

Drimane and coloratane sesquiterpenoids are present in several plants, microorganisms, and marine life. Because of their cytotoxic activity, these sesquiterpenoids have received increasing attention as a source for new anticancer drugs and pharmacophores. Natural drimanes and coloratanes, as well as their semi-synthetic derivatives, showed promising results against cancer cell lines with in vitro activities in the low micro- and nanomolar range. Despite their high potential as novel anticancer agents, the mode of action and structure–activity relationships of drimanes and coloratanes have not been completely enlightened nor systematically reviewed. Our review aims to give an overview of known structures and derivatizations of this class of sesquiterpenoids, as well as their activity against cancer cells and potential modes-of-action. The cytotoxic activities of about 40 natural and 25 semi-synthetic drimanes and coloratanes are discussed. In addition to that, we give a summary about the clinical significance of drimane and coloratane sesquiterpenoids.

Structure-Pungency Relationships and TRP Channel Activation of Drimane Sesquiterpenes in Tasmanian Pepper (Tasmannia lanceolata)

Sensory-guided fractionation of extracts of Tasmanian pepper berries revealed 20 drimane sesquiterpens, among which polygodial, warburganal, and 1β-acetoxy-9-deoxy-isomuzigadial exhibited the lowest pungency threshold concentrations on the tongue surface (0.6-2.8 nmol/cm²) and elicited a dose-dependent calcium influx into mTRPA1 expressing CHO cells with the lowest EC₅₀ values (4.5 ± 1.0 to 16.7 ± 7.5 μmol/L) and a good correlation to oral pungency thresholds (R² = 0.986, linear regression). Calcium imaging assays demonstrated these chemosensates to induce a calcium influx into cultured trigeminal neurons prepared from wildtype (TRPA1^+/+) mice, whereas no calcium influx was observed in neurons from TRPA1 knockout mice (TRPA1^-/-), thus confirming the α,β-unsaturated 1,4-dialdehyde structure to be the required structural motif for a low oral puncency thresholds and activation of the Transient Receptor Potential Channel A1 (TRPA1). Time-resolved NMR experiments confirmed the pungency mediating mechanism for electrophilic drimane sesquiterpene dialdehydes to be different from that found for other electrophilic pungent agents like isothiocyanates, which have been shown to undergo a covalent binding with cysteine residues in TRPA1. Instead, the high-impact chemosensates polygodial, warburganal, and 1β-acetoxy-9-deoxy-isomuzigadial showed immediate reactivity with the ε-amino group of lysine side chains to give pyrrole-type conjugates, thus showing evidence for TRPA1 activation by covalent lysine modification.

Scalarane sesterterpenoids: semisynthesis and biological activity

Aiming to improve the potency and selectivity of scalarane sesterterpenoids, a series of natural and semisynthetic analogues, derived from the cytotoxic naturally abundant sesterterpene heteronemin (1), were evaluated for their in vitro antimicrobial and cytotoxic properties. The new sesterterpenes 16-O-methylsesterstatin 4 (6c), 17, 24-dihydroheteronemin (7a), 16, 25-deacetoxy-17, 24-dihydroheteronemin (7b), and 16-deacetoxy-25-methoxy-17, 24-dihydroheteronemin (7c) were structurally defined via physical data analyses. Scalarane sesterterpenes possessing an unsaturated 1,4-dialdehyde moiety showed potent inhibitory activity against methicillin-resistant Staphylococcus aureus at concentrations that are not significantly cytotoxic to mammalian cells. The structural features for the cytotoxicity of scalarane sesterterpenoids are discussed.