Isolation, Characterization of Undescribed Alkaloids, and Semisynthetic Modifications of Cytotoxic Pyranoacridone Alkaloids from Glycosmis pentaphylla

Two undescribed alkaloids (10 and 11), along with nine known alkaloids (1-9), have been isolated from the stem and root bark of Glycosmis pentaphylla. Among them are carbocristine (11), a carbazole alkaloid first time isolated from a natural source, and acridocristine (10), a pyranoacridone alkaloid first time isolated from the genus "Glycosmis". In vitro cytotoxicity of isolated compounds has been analyzed on breast cancer (MCF-7), lung cancer (CALU-3), and squamous cell carcinoma cell lines (SCC-25). The results demonstrated that compounds are moderately active. In order to study the structural activity relationship of majorly isolated compounds, semisynthetic modifications have been done on majorly isolated compounds such as des-N-methylacronycine (4) and noracronycine (1) to synthesize 11 semisynthetic derivatives (12-22) on functionalizable -NH and -OH groups of the pyranoacridone scaffold at 12th and 6th positions. Semisynthetic derivatives are explored on the same cell lines as isolated compounds, and the results exhibit that semisynthetic compounds showed potent cytotoxic activity compared with naturally isolated compounds. In the case of CALU-3, the dimer at -OH position of noracronycine (1), i.e., compound 22, showed 24-fold better activity with an IC₅₀ of 4.49 μM compared with noracronycine (1) with IC₅₀ 97.5 μM. In MCF-7, the dimer at -OH position of noracronycine (1), i.e., compound 22, showed 14-fold better activity with an IC₅₀ of 13.2 μM compared with noracronycine (1) with IC₅₀ 187 μM.

Studies Directed towards the Synthesis of the Acridone Family of Natural Products: Total Synthesis of Acronycines and Atalaphyllidines

A modular and flexible three-step synthetic strategy has been developed for the synthesis of acridone natural products of biological significance. The tetracyclic core of acridone derivatives has been achieved efficiently in high yield from commercially available anthranilic acid and phenol derivatives via condensation reaction, followed by regioselective annulation. Acridone alkaloids acronycine and noracronycine are synthesized in improved overall yields in fewer steps than the previously reported approaches. The method has further been used for the synthesis of atalaphyllidine and 5-hydroxynoracronycine in excellent yields for the first time. Moreover, the synthetic utility of the present strategy has been showcased by the synthesis of oxa and thia analogues of acronycine alkaloid.

Acridine and its derivatives: a patent review (2009 - 2013)

INTRODUCTION

Acridine derivatives have been extensively explored as potential therapeutic agents for the treatment of a number of diseases, such as cancer, Alzheimer's, and bacterial and protozoan infections. Their mode of action is mainly attributed to DNA intercalation and the subsequent effects on the biological processes linked to DNA and its related enzymes.

AREA COVERED

This review covers the relevant efforts in developing acridine derivatives with enhanced therapeutic potency and selectivity and as fluorescent materials, with particular focus on the newly patented acridine derivatives in 2009 - 2013, acridine drugs in clinical trials and preclinical studies, and other new derivatives that emerged in 2009 - 2013.

EXPERT OPINION

Thousands of acridines with therapeutic and biological activities or with photochemical properties have been developed. In addition, to modify the position and the nature of the substituent on the acridine core, more attention may be paid to the development of azaacridine or other heteroatom-substituted acridine derivatives and their synthesis methods to broaden the application of acridine derivatives. In cancer chemotherapy, the mode of action of acridine derivatives needs to be further studied. Efficient methods for identification and optimization of acridine derivatives to localize at the sites of disease need to be further developed. Moreover, acridine drugs may be combined with such bioactive agents as DNA repair proteins inhibitors to overcome tumor resistance and improve outcomes.