Natural_products_with_atypical_atoms Unveiling_structures_biosynthetic_pathways_and_bioactivities

Natural products with atypical atoms: unveiling structures, biosynthetic pathways, and bioactivities

Terms

• Natural Product: A chemical compound produced by a living organism, typically as a secondary metabolite.
• Nucleophile: An atom, ion, or molecule that donates an electron pair to form a new chemical bond with an electron-deficient species (an electrophile).
• Secondary Metabolite: Organic compounds not directly involved in normal growth or reproduction, often functioning in defense, signaling, or ecological interactions.
• Biosynthesis: The enzyme-mediated production of complex molecules within living organisms.
• Organofluorine Chemistry: The study of organic compounds containing carbon–fluorine (C–F) bonds.
• Fluoride: The anionic form of fluorine (F⁻), used by the rare enzyme fluorinase to initiate biological fluorination.
• Polyketide: A class of secondary metabolites assembled from repeated acetyl and malonyl building blocks by polyketide synthases.
• Polyketide Synthase (PKS): A family of enzymes responsible for the biosynthesis of polyketides.
• Fluorinase: An enzyme that catalyzes biological carbon–fluorine bond formation. The first discovered fluorinase was identified in Streptomyces cattleya.
• Genome Mining: Computational identification of biosynthetic gene clusters and other functional genomic features.
• Metagenomics: The study of genetic material recovered directly from environmental samples.
• Halogenase: An enzyme that catalyzes the incorporation of halogen atoms into organic molecules.
• Quorum Sensing: Cell-to-cell communication in microorganisms through signaling molecules that coordinate population-level behavior.
• Ionophore: A molecule capable of transporting ions across biological membranes.
• Lewis Acid: A chemical species that accepts an electron pair to form a covalent bond.
• Lipophilicity: The tendency of a compound to dissolve in nonpolar solvents or lipid environments.
• Redox: Chemical reactions involving the transfer of electrons through oxidation and reduction.
• Chemical Space: The theoretical universe of all possible chemical compounds and their properties.

Summary

This review surveys naturally occurring compounds containing atypical elements, including:

• Boron
• Fluorine
• Arsenic
• Selenium
• Iodine
• Vanadium
• Molybdenum Although the overwhelming majority of natural products consist of CHON(S) chemistry, evolution has produced specialized enzymatic machinery capable of incorporating these chemically unusual atoms into biologically active molecules. These compounds frequently exhibit unusual chemical stability, redox chemistry, catalytic behavior, and pharmacological activity.

Why atypical atoms are rare

Several factors limit biological incorporation of atypical atoms:

• Low intracellular concentrations.
• Difficult chemical properties.
• Lack of suitable enzyme machinery.
• High energetic cost. For fluorine:
• Fluoride is highly hydrated, making it a poor nucleophile.
• The C–F bond is one of the strongest single bonds in organic chemistry.
• Enzymes therefore struggle both to create and later modify fluorinated molecules.

Fluorinated natural products

Only a handful of genuine biological organofluorine compounds are known. Examples include:

• Fluoroacetate
• Fluorinated fatty acids
• 4-Fluoro-L-threonine
• Nucleocidin Almost all originate from specialized microorganisms or a small number of plants. Known fluorinating organisms possess dedicated fluorination pathways, particularly the fluorinase enzyme## Relevance to MS2Atoms

This paper is highly relevant to the atom identification problem.

MS2Atoms attempts to infer which atoms are present directly from fragmentation spectra before attempting complete molecular identification.

This review highlights why detecting atoms such as:

• Fluorine
• Boron
• Selenium
• Arsenic
• Iodine

is scientifically valuable:

• They are biologically rare.
• They imply specialized biosynthetic pathways.
• They often produce molecules with unusual pharmacological properties.
• They occupy sparsely sampled regions of chemical space.

Consequently, reliable atom prediction can substantially reduce the search space for downstream molecular formula and structure prediction.

Food for thought

• Naturally occurring fluorinated metabolites are exceptionally rare.
• Organisms capable of producing them possess specialized fluorination enzymes.
• Fluorinated compounds frequently function as toxins, antibiotics, or ecological defense molecules.
• Fluorine dramatically alters molecular properties, including:
  • metabolic stability
  • lipophilicity
  • acidity
  • molecular conformation

Consequently, accurately detecting fluorine from MS/MS spectra is not only identifying another element but identifying molecules likely belonging to a unique biosynthetic class.