Monobutyrin, also known as 1-glyceryl monobutyrate or 1-monoacyl-sn-glycerol (C7H14O4, MW 162.18), is a monoacylglycerol formed by esterification of butyric acid (C4:0) at the sn-1 position of glycerol. This compound exhibits documented bioactivity as an angiogenic regulator and is widely used as a functional feed additive.
Chemical Structure
Monobutyrin features a glycerol backbone with a single butanoyl group (-CO(CH2)2CH3) esterified at the primary sn-1 hydroxyl, leaving two free secondary hydroxyl groups. It exists primarily as the R-enantiomer, which represents the bioactive form. Its structural formula is CH2(OCOC3H7)-CH(OH)-CH2OH.
Structural confirmation has been obtained by 1H NMR spectroscopy (ester CH2 δ 4.15 ppm; butyryl CH2 δ 2.35 ppm) and by specific optical rotation [α]D −7.40° (c = 2, pyridine). The compound appears as a colorless to light-yellow liquid with a characteristic ester aroma, a density of approximately 1.09 g/mL, and a refractive index ranging from 1.445 to 1.453.
Physicochemical Properties
Monobutyrin exhibits a boiling point of approximately 153 °C at 7 mmHg and demonstrates moderate solubility in organic solvents such as chloroform and methanol. It is hygroscopic and therefore requires refrigerated storage under inert atmospheric conditions to maintain stability. The compound has an estimated pKa of ~13.2.
In high-purity preparations, free butyric acid content typically remains below 0.5%, while residual glycerol content does not exceed 20%. Monobutyrin displays thermal stability up to 230 °C due to the covalent butyryl–glycerol bond, which confers resistance to degradation under acidic and alkaline conditions.
Biosynthesis and Metabolism
Monobutyrin can be produced via enzymatic transesterification of tributyrin with glycerol or through partial hydrolysis of dibutyrin or tributyrin.
In vivo, microbial lipases or pancreatic carboxyl ester lipase hydrolyze monobutyrin slowly to release free butyric acid. This gradual conversion enables biological activity associated with histone deacetylase inhibition and gene expression modulation, while avoiding the strong odor and rapid dissociation commonly associated with free butyrate administration.