Auxiliary-directed oxidation of ursolic acid by ‘Ru’-porphyrins: chemical modulation of cytotoxicity against tumor cell lines

Biomimetic Chemical Reactions with Natural Products Using Metalloporphyrins and Salen Complexes as Catalysts: A Brief Review

The cytochrome P450 is a superfamily of hemoproteins mainly present in the liver and are versatile biocatalysts. They participate in the primary metabolism and biosynthesis of various secondary metabolites. Chemical catalysts are utilized to replicate the activities of enzymes. Metalloporphyrins and Salen complexes can contribute to the products' characterization and elucidate biotransformation processes, which are investigated during pre-clinical trials. These catalysts also help discover biologically active compounds and get better yields of products of industrial interest. This review aims to investigate which natural product classes are being investigated by biomimetic chemical models and the functionalities applied in the use of these catalysts. A limited number of studies were observed, with terpenes and alkaloids being the most investigated natural product classes. The research also revealed that Metalloporphyrins are still the most popular in the studies, and the identity and yield of the products obtained depend on the reaction system conditions.

Dual function of lectins — new perspectives in targeted photodynamic therapy

Porphyrins and phthalocyanines are photosensitizers (PS) that are used in clinical imaging, detection of cancer cells and are particularly applied in photodynamic therapy (PDT). Many scientists have been focused on the design of different porphyrin compounds. However, similar to other anti-cancer agents, they cannot selectively recognize tumor tissues. Scientists are seeking new methods to overcome this problem and to find appropriate targeted delivery strategies. Plant lectins are especially suitable molecules for such targeting as they preferentially recognize specific antigens on the glycosylated cancer cells. This review will give more detailed information about the dual function of lectins and their interactions with PSs, which is a new perspective in targeted PDT. The implications and potential applications of such studies will also be discussed.

Polymeric structure of a coproporphyrin I ruthenium(II) complex: a powder diffraction study

Porphyrin complexes of ruthenium are widely used as models for the heme protein system, for modelling naturally occurring iron-porphyrin systems and as catalysts in epoxidation reactions. The structural diversity of ruthenium complexes offers an opportunity to use them in the design of multifunctional supramolecular assemblies. Coproporphyrins and metallocoproporphyrins are used as sensors in bioassay and the potential use of derivatives as multiparametric sensors for oxygen and H⁺ is one of the main factors driving a growing interest in the synthesis of new porphyrin derivatives. In the coproporphyrin I Ru^II complex catena-poly[[carbonylruthenium(II)]-μ-2,7,12,17-tetrakis[2-(ethoxycarbonyl)ethyl]-3,8,13,18-tetramethylporphyrinato-κ⁵N,N',N'',N''':O], [Ru(C₄₄H₅₂N₄O₈)(CO)]_n, the Ru^II centre is coordinated by four N atoms in the basal plane, and by axial C (carbonyl ligand) and O (ethoxycarbonylethyl arm from a neighbouring complex) atoms. The complex adopts a distorted octahedral geometry. Self-assembly of the molecules during crystallization from a methylene chloride-ethanol (1:10 v/v) solution at room temperature gives one-dimensional polymeric chains.

New Diterpenes from Azorella spinosa

Two new diterpenes,2-acetoxy-13-hydroxy-mulin-11-ene and 2-acetoxy-mulin-11, 13-diene, have been isolated from the aerial parts of Azorella spinosa and their structures determined by spectroscopic and conventional chemical methods. Furthermore, 2, 13-dihydroxy-mulin-11-ene was obtained using a basic hydrolysis of the first compound. Two diterpenes reported for other Azorella species have also been found, namely mulinolic acid and 13β-hydroxyazorellane, as well as the triterpene lactone of ursolic acid, quercetin, and 7-hydroxycoumarin. The compounds were evaluated using antibacterial, antioxidant and enzymatic assays; no significant activity was detected.

Cytotoxic activity of ursolic acid derivatives obtained by isolation and oxidative derivatization

Structure-activity relationships of ursane-type pentacyclic triterpenes obtained from natural sources and by chemical derivatization are reviewed. Ursolic acid, corosolic acid, and a new ursane-type pentacyclic triterpene, 7,24-dihydroxyursolic acid, were isolated from the methanolic extract of the leaves of the Bangladeshi medicinal plant, Saurauja roxburghii. Derivatization of ursolic acid by oxidation with dioxoruthenium (VI) tetraphenylporphyrins was investigated. Oxidation selectivity on the terpene structure was modulated by the auxiliaries introduced on the tetraphenylporphyrin. The natural triterpenes and oxidized derivatives were tested for cytotoxicity against the C6 rat glioma and A431 human skin carcinoma cell lines. Although they have the same ursane-type pentacyclic triterpene cores, the position and numbers of hydroxyls on the terpene structures significantly affected the activity and the selectivity towards the tested cell lines.

Ursolic acid in cancer prevention and treatment: molecular targets, pharmacokinetics and clinical studies

Discovery of bioactive molecules and elucidation of their molecular mechanisms open up an enormous opportunity for the development of improved therapy for different inflammatory diseases, including cancer. Triterpenoids isolated several decades ago from various medicinal plants now seem to have a prominent role in the prevention and therapy of a variety of ailments and some have already entered Phase I clinical trials. One such important and highly investigated pentacyclic triterpenoid, ursolic acid has attracted great attention of late for its potential as a chemopreventive and chemotherapeutic agent in various types of cancer. Ursolic acid has been shown to target multiple proinflammatory transcription factors, cell cycle proteins, growth factors, kinases, cytokines, chemokines, adhesion molecules, and inflammatory enzymes. These targets can potentially mediate the chemopreventive and therapeutic effects of ursolic acid by inhibiting the initiation, promotion and metastasis of cancer. This review not only summarizes the diverse molecular targets of ursolic acid, but also provides an insight into the various preclinical and clinical studies that have been performed in the last decade with this promising triterpenoid.