3-Hydroxypropionic acid

3-Hydroxypropionic acid (3-HP) is an organic acid with terminal hydroxy and carboxyl reactive groups (figure 1). 3-Hydroxypropionic acid contains two functional groups with different properties, making it suitable for application as a precursor for the synthesis of many optically active substances. Besides, it can also be used as an additive and preservative for food or feed.

Fig. 1 Structure of 3-Hydroxypropionic acid

Biosynthesis of 3-Hydroxypropionic Acid

Compared with petroleum-dependent chemical synthesis which may lead to resource depletion and environmental pollution, biosynthesis of 3-hydroxypropionic acid has attracted more attention due to the utilization of renewable biomass. According to the substrates or intermediates, the biosynthesis pathways include the followings (figure 2)^[1]:

Fig. 2 Main pathways and key enzymes for 3-hydroxypropionic acid biosynthesis. Red arrows indicate CoA-dependent pathway; green arrows indicate CoA independent pathway; yellow arrows indicate Malonyl-CoA pathway; purple arrows indicate the β-alanine pathway; and double-color arrows indicate the common steps of the corresponding pathways.

• Glycerol oxidation via coenzyme A‑dependent pathway

In coenzyme A-dependent glycerol oxidation pathway, glycerol is catalyzed into 3-hydroxypropionaldehyde (3-HPA) by coenzyme B12-dependent glycerol dehydratase (GDHt). Then, 3-hydroxypropionaldehyde is catalyzed into 3-hydroxypropionic acid-CoA by propionaldehyde dehydrogenase (PduP) in the presence of coenzyme A. Lastly, 3-hydroxypropionic acid-CoA is converted to 3-hydroxypropionic acid under the catalysis of phosphotransferase (PduL) and propionate kinase (PduW).

• Glycerol oxidation through coenzyme A‑independent pathway

In coenzyme A-independent pathway, glycerol-based biosynthesis of 3-hydroxypropionic acid involves only two steps. Glycerol is converted to 3-hydroxypropionaldehyde by coenzyme B12-dependent glycerol dehydratase (GDHt); Next, 3-hydroxypropionaldehyde is converted to 3-hydroxypropionic acid by aldehyde dehydrogenase.

• Malonyl-CoA pathway

In malonyl-CoA pathway, acetyl-CoA does not enter tricarboxylic acid (TCA) cycle. Instead, it is converted to malonyl-CoA by acetyl-CoA carboxylase (ACC). The resulting malonyl-CoA is then converted to 3-hydroxypropionic acid by malonyl-CoA reductase (MCR) in two steps.

• β-alanine pathway

Similar to malonyl-CoA pathway, the β-alanine pathway also employs methane sulfonic acid as the precursor for production of 3-hydroxypropionic acid, but methane sulfonic acid is resulted from tricarboxylic acid cycle and β-alanine (figure 2).

Applications

As a hydroxy-functionalized carboxylic acid, 3-hydroxypropionic acid is a promising platform chemical, which can be transformed to a variety of worthy products such as acrylic acid, 3-hydroxypropionaldehyde, acrolein, acrylonitrile, malonic acid, 1,3-propanediol and building blocks for biodegradable polymers (figure 3).

Fig. 3 Applications of 3-hydroxypropionic acid as a platform compound

The two most important present applications of 3-hydroxypropionic acid are the production of acrylic acid and poly(3-hydroxypropionic acid). Acrylic acid is able to be obtained by dehydrating 3-hydroxypropionic acid, and acrylic acid-derived products are widely used in paints, paper, baby diapers, adhesives, textiles, specialty coatings, and superabsorbers. While poly(3-hydroxypropionic acid) has good mechanical properties and can be hydrolyzed enzymatically, mainly used for making surgical products.

Our 3-Hydroxypropionic Acid

Properties of our 3-Hydroxypropionic acid (3-HP) are listed below.

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Reference

1. Zhao, P., & Tian, P. Biosynthesis pathways and strategies for improving 3-hydroxypropionic acid production in bacteria. World Journal of Microbiology and Biotechnology, 2021, 37(7).

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