New antineoplastic prenylhydroquinones. Synthesis and evaluation

Bioactive Prenyl- and Terpenyl-Quinones/Hydroquinones of Marine Origin †

The sea is a rich source of biological active compounds, among which terpenyl-quinones/hydroquinones constitute a family of secondary metabolites with diverse pharmacological properties. The chemical diversity and bioactivity of those isolated from marine organisms in the last 10 years are summarized in this review. Aspects related to synthetic approaches towards the preparation of improved bioactive analogues from inactive terpenoids are also outlined.

Convergent approach to complex spirocyclic pyrans: practical synthesis of the oxa-pinnaic acid core

The enantioselective synthesis of the oxa-pinnaic acid framework has been achieved through internal asymmetric induction. The synthetic strategy pursued illustrates the adaptability of the Achmatowicz oxidative rearrangement for the synthesis of complex spirocyclic pyrans starting from tertiary alcohols.

Comparison of the biological properties of several marine sponge-derived sesquiterpenoid quinones

Eight naturally occurring marine-sponge derived sesquiterpenoid quinones were evaluated as potential inhibitors of pyruvate phosphate dikinase (PPDK), a C4 plant regulatory enzyme. Of these, the hydroxyquinones ilimaquinone, ethylsmenoquinone and smenoquinone inhibited PPDK activity with IC50's (reported with 95% confidence intervals) of 285.4 (256.4-317.7), 316.2 (279.2-358.1) and 556.0 (505.9-611.0) microM, respectively, as well as being phytotoxic to the C4 plant Digitaria ciliaris. The potential anti-inflammatory activity of these compounds, using bee venom phospholipase A2 (PLA2), was also evaluated. Ethylsmenoquinone, smenospongiarine, smenospongidine and ilimaquinone inhibited PLA2 activity (% inhibition of 73.2 +/- 4.8 at 269 microM, 61.5 +/- 6.1 at 242 microM, 41.0 +/- 0.6 at 224 microM and 36.4 +/- 8.2 at 279 microM, respectively). SAR analyses indicate that a hydroxyquinone functionality and a short, hydroxide/alkoxide side-chain atC-20 is preferred for inhibition of PPDK activity, and that a larger amine side-chain at C-20 is tolerated for PLA2 inhibitory activity.

Synthesis and cytotoxicity of new heterocyclic terpenylnaphthoquinones

Several 2-arylamino-, 2-aryloxy- and 2-arylsulfanyl-6(7)-alkyl-1,4-naphthoquinones (NQ) have been prepared and further transformed into the corresponding heterocyclic-fused naphthoquinones by palladium (II)-catalyzed oxidative cyclization. The compounds synthesized have been evaluated against neoplastic cell lines. The extension of the polycyclic system clearly decreased the cytotoxic potency of the 2-substituted terpenylnaphthoquinones.

New cytotoxic-antineoplastic prenyl-1,2-naphthohydroquinone derivatives

Several new prenylnaphthohydroquinone derivatives have been prepared through the Diels-Alder condensation between alpha-myrcene and 1,2-benzoquinone and evaluated for their cytotoxic activity against A-549, HT-29 and MB-231 cultured cell lines. All of them have shown GI50 values in the microM level.

Synthesis, characterisation and cytotoxicity of chloro derivatives of prenylnaphthohydroquinone

From the Diels-Alder adduct between alpha-myrcene and 2-chloro-1,4-benzoquinone, a family of chloro derivatives of prenylnaphthohydroquinone have been synthesised and evaluated for their cytotoxicity against 14 neoplastic cell lines.

Synthesis and cytotoxicity of new aminoterpenylquinones

Several 6(7)-alkyl-1,4-naphthoquinones (NQ) have been prepared by cycloaddition reactions between the monoterpene alpha-myrcene and p-benzoquinones and halogen and nitrogen-containing functional groups have been introduced at the C-2 position of the naphthoquinone ring via nucleophilic addition or substitution reactions. These substituents at positions 2/3 of the NQ clearly influence the cytotoxic potency of this type of compound. Of particular interest is substitution by arylamino, specifically p-oxyarylamino, groups, which considerably enhance their bioactivity and selectivity.

Cytotoxic–antineoplastic activity of acetyl derivatives of prenylnaphthohydroquinone

Several acetyl derivatives of prenylnaphthohydroquinone have been synthetized and evaluated for their cytotoxicity against A-549 human lung carcinoma and H-116 human colon carcinoma neoplastic cells. The IC50 values against A-549 are compared with those observed for previously reported unsubstituted derivatives.

Farnesyl-O-acetylhydroquinone and geranyl-O-acetylhydroquinone suppress the proliferation of murine B16 melanoma cells, human prostate and colon adenocarcinoma cells, human lung carcinoma cells, and human leukemia cells

Farnesyl-O-acetylhydroquinone (IC(50)=2.5 microM/l) suppressed the proliferation of murine B16F10 melanoma cells with a potency much greater than those of farnesol (IC(50)=45 microM/l) and farnesyl anthranilate (IC(50)=46 microM/l), its alcohol, and ester counterparts with proven anti-tumor activities in vivo. Geranyl-O-acetylhydroquinone (IC(50)=5.1 microM/l) also had a much-improved activity compared to geraniol (IC(50)=160 microM/l) and geranyl anthranilate (IC(50)=30 microM/l). The suppression by farnesyl-O-acetylhydroquinone was concentration- and time-dependent and was accompanied by arrest of cell cycle at G1 and G2/M phases as shown by flow cytometry. Farnesyl-O-acetylhydroquinone and lovastatin had additive impact on B16 cell proliferation. Farnesyl-O-acetylhydroquinone also suppressed the proliferations of human cancer cells HL-60, DU145, PC-3, LNCaP, Caco-2, and A549. Our results suggested that farnesyl derivatives, suppressors of tumor 3-hydroxy-3-methylglutaryl coenzyme A reductase activities, have potential as chemopreventive or chemotherapeutic agents.

Unified synthesis of quinone sesquiterpenes based on a radical decarboxylation and quinone addition reaction

A unified synthesis of several quinone sesquiterpenes is described herein. Essential to this strategy is a novel radical addition reaction that permits the attachment of a fully substituted bicyclic core 16 to a variably substituted quinone 10. The addition product 15 can be further functionalized, giving access to natural products with a high degree of oxygenation at the quinone unit. The quinone addition reaction is characterized by excellent chemoselectivity, taking place only at conjugated and unsubstituted double bonds, and regioselectivity, being strongly influenced by the resonance effect of heteroatoms located on the quinone ring. These features were successfully applied to the synthesis of avarol (1), avarone (2), methoxyavarones (4, 5), ilimaquinone (6), and smenospongidine (7), thereby demonstating the synthetic value of this new method.

New selective cytotoxic diterpenylquinones and diterpenylhydroquinones

A new series of diterpenylquinone/hydroquinones has been prepared by Diels-Alder cycloaddition between three labdanic diterpenoids (myrceocommunic acid, methyl myrceocommunate, and myrceocommunyl acetate) and p-benzoquinone or 1,4-naphthoquinone. Influences of the quinone/hydroquinone fragment and other structural features, such as the different functionalities in the terpenic core, are considered in relation to the cytotoxicity toward neoplastic cells and the selectivity of these diterpenylnaphthoquinones/hydroquinones and anthraquinones. Several compounds showed IC50 values under the micromolar level, and four of these derivatives were evaluated at the NCI screening panel. The results showed an important selectivity toward renal cancer lines, identifying these compounds as a very promising group of antineoplastics.