Madangamines are a group of polycyclic alkaloids from marine sponges which have biomedical interest due to their cytotoxic activity. A research group from the University of Barcelona (UB) has just described in a paper published in the journal Angewandte Chemie International Edition the first total synthesis of madangamine D, a scientific discovery in the field of organic chemistry. The paper, which represents the first total synthesis of an alkaloid of the madangamine group, is authored by Joan Bosch, Mercedes Amat, Roberto Ballette, Maria Pérez, and Stefano Proto, from the Organic Chemistry Laboratory of the Faculty of Pharmacy and the Institute of Biomedicine of UB (IBUB).
Marine molecules of biomedical interest
Sponges are a group of marine organisms rich in bioactive products. However, it is usually very difficult to develop in-depth studies about their biological activity because they contain isolated small quantities of these products. Madangamines A and F have shown significant cytotoxicity against a number of tumour cell lines. In the study, madangamine D showed significant in vitro cytotoxic activity against human colon and pancreas cancer cell lines.
To successfully accomplish the synthesis of madangamine D, experts use the knowledge attained by the UB research group in order to use phenylglycinol-derived bicyclic lactams in the enantioselective synthesis of piperidine-containing alkaloids. By using this type of lactam, the diazatricyclic ABC core, common to all madangamines, was synthetized in a completely stereocontrolled way. Once the core is obtained, madangamine D macrocyclic rings are elaborated.
A 27-phase synthesis process
This is the first total synthesis of a sponge isolated marine alkaloid with complex structure. The synthesis has enabled for the first having a pure sample of this natural product, as when it was isolated, in really small quantities, madangamine D was not pure as it was mixed with other alkaloid of the same group (madangamine E). Consequently, the UB research group was able to carry out bioactivity assays. Furthermore, enantioselective synthesis enabled to prove the configuration of this alkaloid family.
Besides difficulties inherent in a synthetic process with a high number of synthesis phases -- 27 in this case -- , the most difficult phases are the stereoselective formation of stereo cores present in the natural product and the alkaloid's construction of macrocyclic rings.
A scientific milestone in the field of organic synthesis
Authors explain that "it is an unprecedented synthesis process of alkaloids of the madangamine group. Previous preparations of diazatricyclic ABC core of these alkaloids were done, but in racemic series and, in most cases, without the functionality needed to build macrocyclic rings later." In fact, the first enantioselective synthesis of the diazatricyclic ABC core of madangamines with adequate functionality to access these natural products was described in 2010 by the UB research group, which is part of the Research and Development Center of Organic Synthesis for Chemical and Pharmaceutical Companies (SINTEFARMA). More recently, the UB research group developed its own methodology to synthetize other alkaloids of this group of molecules by means of a common intermediate.
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