Enantioselective synthesis and evaluation of 4-styryldihydropyrimidin-2-thiones as anti-proliferative agents

Asymmetric organocatalysis: an enabling technology for medicinal chemistry

The efficacy and synthetic versatility of asymmetric organocatalysis have contributed enormously to the field of organic synthesis since the early 2000s. As asymmetric organocatalytic methods mature, they have extended beyond the academia and undergone scale-up for the production of chiral drugs, natural products, and enantiomerically enriched bioactive molecules. This review provides a comprehensive overview of the applications of asymmetric organocatalysis in medicinal chemistry. A general picture of asymmetric organocatalytic strategies in medicinal chemistry is firstly presented, and the specific applications of these strategies in pharmaceutical synthesis are systematically described, with a focus on the preparation of antiviral, anticancer, neuroprotective, cardiovascular, antibacterial, and antiparasitic agents, as well as several miscellaneous bioactive agents. The review concludes with a discussion of the challenges, limitations and future prospects for organocatalytic asymmetric synthesis of medicinally valuable compounds.

Eco-friendly and Enantiospecific Biginelli Synthesis Using (+)-Myrtenal as the Substrate - An Impeccable and Unequivocal Analysis of the Product

BACKGROUND

We found in the literature, an excellent review of the Biginelli reaction that addresses the methodologies for obtaining enantiopure dihydropyrimidinones (DHPMs). In 1992, optically pure DHPMs were obtained by fractional crystallization of the diastereomeric ammonium salt derivative with (S)-(-) and (R)- (+)-α-methyl benzylamine and by other chiral resolution techniques, such as chiral high-performance liquid chromatography (HPLC). Asymmetric syntheses of these compounds are also explained in the literature. The main strategy is to use acid catalysts such as organophosphates, organometallic complexes, amines and diamines, nanocomposites, and chiral ionic liquids, e.g., L-prolinium sulfate (Pro2SO4).

OBJECTIVE

The objective was to study the Biginelli reaction with a chiral aldehyde.

METHODS

A mixture of ethyl acetoacetate (0.26 g, 3 mmol), urea (0.18 g, 3 mmol) and ethyl lactate (EL) (1 mL) was left under heating at 70°C and stirring for 1 h. Next, (-)-(1R)-myrtenal (0.45 g, 3 mmol) was added, and the medium was heated for 5 h more until the formation of a white solid. Ten millilitres of distilled water was added, and the product was extracted with CH2Cl2 (3 x 4 mL). The solvent was evaporated, and the product was recrystallized from ethanol-water.

RESULTS AND DISCUSSION

(+)-Myrtenal was used as a chiral substrate for a study that led to ethyl (R)-4-((1R,5S)- 6,6-dimethylbicyclo [3.1.1]hept-2-en-2-yl)-6-methyl-2-oxo-1,2,3,4-tetrahydropyrimidine-5-carboxylate by the Biginelli synthesis using EL as a green solvent. The result is the first example of the enantiospecific Biginelli reaction. The product was exhaustively characterized by several physical analysis methods, i.e., 1H, 13C and 2D nuclear magnetic resonance (NMR) spectroscopies, infrared (IR) spectroscopy, mass spectrometry (MS), and high-resolution MS (HRMS), and its structure was unequivocally elucidated by X-ray crystallography.

CONCLUSION

Compound (4R)-4-(6,6-dimethylbicyclo[3.1.1]hept-2-en-2-yl)-6-methyl-2-oxo-1,2,3,4- tetrahydropyrimidine- 5-ethyl carboxylate is the first example of the enantiospecific Biginelli reaction. In addition, the process has the advantage of using EL as a green solvent. The product was characterized by 1H, 13C, and 2D NMR and IR spectroscopy, MS, HRMS, and X-ray crystallography.

Synthesis, modification, and cytotoxic evaluation of 2,3-secotriterpenic β-ketoesters

A set of β-ketoesters was synthesized from 2,3-seco-18αH-oleanane and 2,3-secolupane bromomethyl ketones. Additionally, hydroxy derivatives with the A-seco- or five-membered A ring were obtained as a result of the reduction or of alkaline hydrolysis of acetic acid β-ketoesters 4, 9. Cytotoxic screening revealed the compound 4 with marked activity (IC₅₀ 3.07-3.61 µM) against the HCT 116, MS, RD TE32 cancer cells. The studies of the cytotoxic mechanism enabled elucidating the fact that treatment of the HCT 116 cells with compound 4 for 18 h leads to induction of apoptosis in a dose-dependent manner. This observation was confirmed by registration of chromatin condensation, by the fluorescence increased during Annexin V-FITC staining, and by appearance of a sub-G0 peak in the cell cycle analysis with DAPI. Compound 4 also inhibited migration of cancer cells in the wound healing assay.