A simple and practical approach to enantiomerically pure (S)-3-hydroxy-γ-butyrolactone: synthesis of (R)-4-cyano-3-hydroxybutyric acid ethyl ester

Production of Optically Pure (S)-3-Hydroxy-γ-butyrolactone from d-Xylose Using Engineered Escherichia coli

Biocatalysis has advantages in asymmetric synthesis due to the excellent stereoselectivity of enzymes. The present study established an efficient biosynthesis pathway for optically pure (S)-3-hydroxy-γ-butyrolactone [(S)-3HγBL] production using engineered Escherichia coli. We mimicked the 1,2,4-butanetriol biosynthesis route and constructed a five-step pathway consisting of d-xylose dehydrogenase, d-xylonolactonase, d-xylonate dehydratase, 2-keto acid decarboxylase, and aldehyde dehydrogenase. The engineered strain harboring the five enzymes could convert d-xylose to 3HγBL with glycerol as the carbon source. Stereochemical analysis by chiral GC proved that the microbially synthesized product was a single isomer, and the enantiomeric excess (ee) value reached 99.3%. (S)-3HγBL production was further enhanced by disrupting the branched pathways responsible for d-xylose uptake and intermediate reduction. Fed-batch fermentation of the best engineered strain showed the highest (S)-3HγBL titer of 3.5 g/L. The volumetric productivity and molar yield of (S)-3HγBL on d-xylose reached 50.6 mg/(L·h) and 52.1%, respectively. The final fermentation product was extracted, purified, and confirmed by NMR. This process utilized renewable d-xylose as the feedstock and offered an alternative approach for the production of the valuable chemical.

Selective continuous flow synthesis of hydroxy lactones from alkenoic acids

The first in-flow selenium-mediated catalysis has been realized under eco-friendly conditions to convert alkenoic acids into hydroxy lactones with a high regio- and diastereo-selectivity ratio.

Biorefineries for the production of top building block chemicals and their derivatives

Due to the growing concerns on the climate change and sustainability on petrochemical resources, DOE selected and announced the bio-based top 12 building blocks and discussed the needs for developing biorefinery technologies to replace the current petroleum based industry in 2004. Over the last 10 years after its announcement, many studies have been performed for the development of efficient technologies for the bio-based production of these chemicals and derivatives. Now, ten chemicals among these top 12 chemicals, excluding the l-aspartic acid and 3-hydroxybutyrolactone, have already been commercialized or are close to commercialization. In this paper, we review the current status of biorefinery development for the production of these platform chemicals and their derivatives. In addition, current technological advances on industrial strain development for the production of platform chemicals using micro-organisms will be covered in detail with case studies on succinic acid and 3-hydroxypropionic acid as examples.

Uses and production of chiral 3-hydroxy-gamma-butyrolactones and structurally related chemicals

Enantiopure (S)-3-hydroxy-gamma-butyrolactone (HGB) and its structurally related C3-C4 chemicals are an important target for chiral building blocks in synthetic organic chemistry. For the production of these compounds, more economical and practical synthetic routes are required. To date, chiral HGBs have been produced from petrochemicals and biomass, especially malic acids and carbohydrates. This report provides a short review on the production and application of enantiopure HGBs and their related compounds. Emphasis is focused mainly on synthetic routes using biocatalysis (microbial and chemoenzymatic) and application of these compounds. Biological methods have concentrated on devising different kinds of enzymes for the synthesis of the same compound as shown in the case of hydroxynitrile, a key intermediate of synthetic statins, and integrating unit processes for the optically active HGBs and 4-chloro-3-hydroxybutyrate with recombinant microorganisms expressing multiple enzymes. Chemical methods involve selective hydrogenation of carbohydrate-based starting materials. Both types of pathways will require further improvement to serve as a basis for a scalable route to HGBs and related compounds. Several of their synthetic applications are also introduced.