Valproic acid

February 28, 2022
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Valproic acid (VPA), formally 2-propylpentanoic acid, is a low–molecular weight branched-chain fatty acid. It is a derivative of valeric (pentanoic) acid1, which occurs naturally in valerian (Valeriana officinalis), an Eastern Hemisphere flowering plant.

VPA has been known since at least the 1880s, when it was synthesized by American chemist Beverly S. Burton. In 1915, a monumental work on optically active fatty acids by Emil Abderhagen and Egon Eichwald at the University of Halle (Germany) reported that VPA was optically active, even though an inspection of its structure shows that that cannot be true.

VPA is widely used for treating several diseases, including epilepsy and bipolar disorder. Until the 1960s, it was used only as a solvent for pharmaceuticals and some industrial chemicals; but in 1963, George Carraz and colleagues at Laboratoire Berthier (Grenoble, France) discovered that all of the compounds they were testing for anticonvulsant activity gave positive results when they were dissolved in VPA. This serendipitous finding led to France’s approval of VPA for treating epilepsy in 1967. The US Food and Drug Administration granted similar approval in 1978.

VPA is well known for inhibiting histone deacetylases, enzymes that allow histone proteins to wrap DNA more tightly than they otherwise would. It also has the ability to reduce the stability of certain proteins, including Cas9 (CRISPR-associated protein 9), which plays an important role in prokaryotic adaptive immunity. Its precise mechanism-of-action for destabilizing Cas9, however, is still largely unknown.

Valproic acid hazard information

Hazard class* GHS code and hazard statement
Acute toxicity, oral, category 4 H302—Harmful if swallowed Chemical Safety Warning
Skin corrosion/irritation, category 2 H315—Causes skin irritation Chemical Safety Warning

Serious eye damage/eye irritation, category 2A

H319—Causes serious eye irritation Chemical Safety Warning
Reproductive toxicity, category 1A H360—May damage fertility or the unborn child Chemical Safety Warning

*Globally Harmonized System (GHS) of Classification and Labeling of Chemicals. Explanation of pictograms.

MOTW update

Phosphorus pentoxide1 (P4O10) was the Molecule of the Week for September 8, 2008. It is a powerful drying agent that can also be used to remove the elements of water from organic and inorganic compounds.

P4O10 has also found use as a metal-free acid catalyst. In a recent example, Evgeny A. Mostovich and colleagues at Novosibirsk State University (Russia) used it to promote the cyclization of di[aryl(heteroaryl)methyl]malonic acids en route to fused, π-extended spiro[4.4]nonane-1,6-diones, which may have valuable optoelectronic applications.

1. CAS Reg. No. 16752-60-6.

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Valproic acid fast facts

CAS Reg. No. 99-66-1
Pentanoic acid, 2-propyl-
Empirical formula C8H16O2
Molar mass 144.21 g/mol
Appearance Colorless liquid
Boiling point 222 °C
Water solubility 1.3 g/L
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