Chemists have invented a new chemical method to synthesize cimastatin, a natural compound with antibiotic potential. A new strategy for the production of natural compounds can also be used to produce variants with stronger antimicrobial activity.
Chemists at the Massachusetts Institute of technology have developed a new method to synthesize himastatin, a natural compound with potential to become an antibiotic.
Using their new synthesis method, researchers can not only produce himastatin, but also produce molecular variants, some of which also show antibacterial activity. They also found that this compound seems to kill bacteria by destroying their cell membranes. Researchers now hope to design other molecules with stronger antibiotic activity.
“What we want to do now is to understand the molecular details of how it works, so that we can design structural patterns that better support this mechanism of action.” Mohammad movassaghi, a professor of chemistry at the Massachusetts Institute of technology and one of the senior authors of the study, said: “our main work now is to understand more about the physical and chemical properties of this molecule and how it interacts with the membrane.”
Brad pentelute, a professor of chemistry at the Massachusetts Institute of technology, is also a senior author of the study published today in the journal Science. Kyan D’Angelo, a graduate student at the Massachusetts Institute of technology, is the main author of this study, and Carly schissel, a graduate student, is also one of the authors.
Cimastatin is produced by a soil bacterium and was first discovered in the 1990s. In animal experiments, it was found to have anticancer activity, but the required dose was toxic and side effects. Movassaghi said that this compound also shows potential antibacterial activity, but this potential has not been explored in detail.
Himastatin is a complex molecule composed of two identical subunits, called monomers, which combine to form dimers. The two subunits connect the six carbon ring of one monomer and the same ring of the other monomer by a bond.
This carbon carbon bond is critical to the antibacterial activity of the molecule. In previous efforts to synthesize himastatin, researchers have tried to form this bond with two simple subunits, and then add more complex chemical groups to the monomers.
The MIT team, inspired by the way the bacteria react to produce cimastatin, took a different approach. These bacteria have an enzyme that can connect two monomers in the last step of synthesis, turning each carbon atom that needs to be connected into a highly active free radical.
In order to simulate this process, researchers first constructed complex monomers using amino acid building blocks, which benefited from the rapid peptide synthesis technology previously developed by pentelute laboratory.
D’Angelo said: “by using solid-phase peptide synthesis, we can quickly complete many synthesis steps and easily mix and match building blocks.” “This is just one of the very helpful ways we have worked with pentelute labs.”
The researchers then used a new dimerization strategy developed by movassaghi’s laboratory to link the two complex molecules together. This new dimerization reaction is based on the oxidation of aniline to form carbon radicals in each molecule. These radicals can react to form carbon carbon bonds, which hook the two monomers together. Using this approach, researchers can create dimers containing different types of subunits, except for naturally occurring himastatin dimers.
Movassaghi said: “the reason we are excited about this dimerization reaction is that it allows you to really diversify the structure and quickly obtain other potential derivatives.”
One of the variants created by the researchers was fluorescently labeled, and they used it to visualize how himastatin interacts with bacterial cells. Using these fluorescent probes, the researchers found that the drug accumulated on the bacterial cell membrane. This led them to hypothesize that it works by destroying the cell membrane, which is also the mechanism for the use of at least one FDA approved antibiotic, daptomycin.
The researchers also designed several other himastatin variants by exchanging different atoms of specific parts of the molecule, and tested their antibacterial activities against six bacterial strains. They found that some of these compounds have strong activity, but only if they contain a naturally occurring monomer and a different monomer.
“By combining two complete half molecules together, we can produce a derivative of himastatin with only one fluorescent label. Only with this version can we conduct microscopic studies to provide evidence for the localization of himastatin in the bacterial membrane, because the symmetric version of the two labels does not have the correct activity,” said D’Angelo.
Researchers now plan to design more variants, which they hope may have stronger antibiotic activity.
“We have identified positions that can be derived and these positions may retain or enhance trading activities. What really excites us is that a large number of derivatives obtained through this design process retain their antibacterial activity,” movassaghi said.