Graphical abstract

The reductive carbonyl coupling leading to 1,2-diols, known as pinacol coupling, is conceptually the most direct approach that leads to this structural pattern. From the nineties, exciting developments have resulted in efficient protocols to the coupling of two different carbonyl compounds mixed in approximately equimolar amounts. This article reports the progress that has been made so far and the challenges existing in the methods and their general synthetic application to the construction of complex bioactive substances.

An efficient method is proposed for obtaining tetrahydrobenzo[a]xanthene-11-ones and tetrahydro-[1,3]-dioxolo[4,5-b]xanthen-9-ones. The method is based on the use of p-sulfonic acid calix[n]arenes as catalysts under solvent-free conditions. The antiproliferative activity of fifty-nine xanthenones against six human cancer cells was studied. The capacity of all compounds to inhibit cancer cell growth was dependent on the histological origin of the cells. QSAR studies indicate that among compounds derived from β-naphthol the most efficient compounds against glioma (U251) and renal (NCI-H460) cancer cells are those having higher hydrogen bonding donor ability.

Graphical abstract

Nature is an irrefutable source of inspiration for the modern man in many aspects. The observation and understanding of nature have allowed the development of new materials, new sources of energies, new drugs etc. Specifically, natural products provide a great contribution to the development of new agents for the treatment of infections and antitumor agents. However, obtaining natural products directly from animals, fungi, bacteria, plants etc has been considered not enough to attend the high demand by pharmaceutical industries. In this regard, various strategies based on biotechnological processes or synthetic approaches have been developed. In this scenario the total synthesis can be undoubtedly a useful and powerful tool for obtaining higher amounts of natural products and/or structural modifications thereof. Herein, we emphasize successful examples of total synthesis of galanthamine, morphine, paclitaxel and podophyllotoxin - natural products approved as pharmaceuticals.