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Heterocycles: The chemical compounds that know no bounds

Oct. 7, 2017

Have you ever wondered just how many heterocyclic compounds exist in nature? As the largest and most-varied family of organic compounds, heterocycles seem to turn up everywhere. In fact, more than half of all known organic compounds are heterocycles. They play vital roles in nucleic acids, in most biomass, and in the core structures of mono and polysaccharides. So what exactly are these structures, and how did they come to be one of the most widely used compounds in chemistry?

The chemistry of heterocycles

A heterocyclic compound is a cyclic compound that has carbon and at least one other element as part of its ring structure. Their general structure resembles cyclic organic compounds that contain rings of only carbon. However, the presence of heteroatoms such as nitrogen, oxygen, or sulfur gives heterocyclic compounds distinct physical and chemical properties. For instance, chemically speaking, heterocycles are more flexible and better able to respond to the many demands of biochemical systems than other molecular structures.

Though these compounds have been around for millions of years, heterocycles were only discovered in the 1800s following the rise of organic chemistry techniques. By isolating compounds from various sources, scientists uncovered the heterocyclic structure. Initially identified in uric acid, the compounds were soon found to be present in the majority of biological matter.

The basis of life as we know it?

Heterocyclic compounds, with their numerous variations, play key roles in the biochemical reactions in almost all living things. Fundamental activities such as energy delivery, nerve impulse transmission, metabolism and the replication of genetic material are all based on chemical reactions involving heterocyclic compounds like vitamins, enzymes, ATP, RNA, DNA and hormones.

The reason heterocycles are so ubiquitous is that they have the unique ability to adapt to their environment, such as the pH of a medium, allowing them to change between acid and base, forming anions or cations as needed. Nature takes advantage of this versatility by using them in an extraordinary range of reactions. Some heterocyclic compounds can interact with electrophilic reagents, or nucleophiles, or even both. Some can be oxidized but resist reduction, while others can be hydrogenated but are stable toward oxidation. Furthermore, some heterocycles can produce stable complexes with metal ions a significant biochemical accomplishment.

Conversion, discovery, and synthesis, oh my!

With their wide distribution in nature and necessity in a plethora of biological processes, it is no wonder heterocycles have become popular tools in the lab. By mimicking their flexibility in natural chemical reactions, we can manipulate these ringed structures to create new properties that aid us in applications such as product conversion, drug discovery and new compound synthesis. Heterocyclic chemistry is now so prevalent in science that 65% of organic chemistry literature discusses heterocyclic moieties!

Heterocyclic compounds are commonly used as a vehicle for the synthesis of other compounds. Simply incorporating different substituents to the ring can change the properties and activity of a target compound, depending on the positioning. Indeed, this phenomenon has been utilized in the fight against bacterial infection, where heterocyclic derivatives of purines and pyrimidines can act as antibiotics by interfering with the target’s DNA synthesis. Puromycin is one such antibiotic, containing a nucleic acid base. By understanding the flexibility of these compounds, chemists can modify a structure to meet a particular need by altering the heterocyclic component.

Because heterocycles participate in many, many cellular processes in the human body, they have also become key to drug discovery itself. Heterocyclic compounds provide the basis for many pharmaceuticals and treatments for diseases such as cancer. Their versatility in structure and function allows them to play a key role in the multiple metabolic pathways and cellular processes within cancer pathology. Of the novel molecular anticancer agents approved by the FDA between 2010 and 2015, almost two-thirds contained heterocyclic rings within their structures!

And one last thing…

Given all of this, it is not surprising that a great deal of research focuses on the methods of synthesis and understanding the properties of heterocyclic compounds. Of the twenty amino acids commonly found in different proteins, three (histidine, proline and tryptophan) are heterocyclic. Not to mention chlorophyll and heme (derivatives of the porphyrin ring system) the components required for photosynthesis and oxygen transport in plants and animals. Even essential dietary ingredients such as thiamine (vitamin B1), riboflavin (vitamin B2), pyridoxol (vitamin B6), nicotinamide (vitamin B3) and ascorbic acid (vitamin C) are heterocyclic compounds. By increasing our understanding of these amazing structures, the variations and new functions we can cultivate just might be endless!

Heterocyclic rings poster

What synthetic route will you take next? Be it in nerve impulse transmission or therapeutic drug development, heterocyclic compounds have a habit of cropping up all over the place. Receive your complimentary poster to see a snapshot of the many heterocyclic ring systems there are out there.


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