Bacterial resistance to drugs leads pharmaceutical labs to be in constant search for new antibiotics to treat the same diseases. For the last thirty years, the sea bottom has yielded a wealth of substances with properties of interest to the pharmaceutical industry. Isolated from a marine microorganism off the coast of Alicante by the company BioMar, baringolin shows promising antibiotic activity at a very low concentration. The Combinatorial Lab headed by Fernando Albericio at the Institute for Research in Biomedicine (IRB Barcelona), which collaborates with BioMar, has now synthesized this molecule and revealed its structure. Today's results open up the possibility to better understand how this substance works and to design derivatives to turn into a viable drug in the next 10 years. These findings are advanced in todays' online edition of Angewandte Chemie, the scientific journal of reference in chemistry.

The researcher Xavier Just-Baringo, who is doing his PhD in the Combinatorial Chemistry Lab, has spent the last four years studying the structural composition of baringolin and has reconstructed this molecule in the lab as if it were 3D a puzzle of atoms that can be joined up in many ways. "This substance has 128 possible structural configurations but only one is an exact replica of the natural peptide. We have been able to find it via 39 synthesis steps," explains Just-Baringo who has had the privilege to name the new compound.

The researchers have finely tuned the organic synthesis of the natural peptide and several analogues and will address the biological activity of these molecules and attempt to improve their pharmacological and pharmacokinetic properties. Through collaboration with the Department of Pharmacology at the Hospital Clínic de Barcelona, they will test the analogues against several strains of gram-positive bacteria, one of the two large groups into which bacteria are classified and against which baringolin has shown inhibitory activity.

Thiopeptides: a new family of antibiotics

Structurally speaking, baringolin is a thiopeptide. These molecules are a new family of antibacterial agents of terrestrial and marine origin, and about 100 have been identified to date. "There is only one thiopeptide on the market for the treatment of bacterial infections, thiostrepton (Panolog), and it is used in veterinary medicine for skin infections. Nothing is available for humans yet," explanis Mercedes Álvarez, associate researcher in the lab, senior professor at the University of Barcelona (UB), and supervisor of the study. The main drawback of thiopeptides is that they show low solubility. For baringolin to be viable as a drug, its solubility must be improved because antibiotics are administered orally or intravenously. "Using the analogues, we aim to improve this feature and identify the parts of the molecule responsible for their antibiotic activity in order to be able to design new more active and smaller analogues," says Álvarez.

"We have taken the first step towards achieving a future drug," says Albericio. "Along the way we have learnt how to synthesize natural molecules and have developed new methods," adds the head of the group and senior professor at the UB. The final objective of the lab is to achieve the total synthesis of natural substances, the last two of which have been thiocoralin, an antitumoral agent that belongs to PharmaMar, and baringolin, belonging to BioMar. "The synthesis of natural products in the lab has a double justification. One is environmental, to protect species that hold substances of pharmacological interest, and the other is commercial, as manufacturing a drug on a large scale is viable only if its production can be ensured on an industrial scale," explain the researchers.