A chemo-enzymatic route to synthesize (S)-γ-valerolactone from levulinic acid

Microbial and enzymatic conversion of levulinic acid, an alternative building block to fermentable sugars from cellulosic biomass

Levulinic acid (LA) is an important chemical building block listed among the top 12 value-added chemicals by the United States Department of Energy, and can be obtained through the hydrolysis of lignocellulosic biomass. Using the same approach as in the catalytic production of LA from biomass, catalytic methods to upgrade LA to higher value chemicals have been investigated. Since the discovery of the catabolic genes and enzymes in the LA metabolic pathway, bioconversion of LA into useful chemicals has attracted attention, and can potentially broaden the range of biochemical products derived from cellulosic biomass. With a brief introduction to the LA catabolic pathway in Pseudomonas spp., this review summarizes the current studies on the microbial conversion of LA into bioproducts, including the recent developments to achieve higher yields through genetic engineering of Escherichia coli cells. Three different types of reactions during the enzymatic conversion of LA are also discussed. KEY POINTS: • Levulinic acid is an alternative building block to sugars from cellulosic biomass. • Introduction of levulinic acid bioconversion with natural and engineered microbes. • Initial enzymatic conversion of levulinic acid proceeds via three different pathways. • 4-Hydroxyvalerate is one of the target chemicals for levulinic acid bioconversion.

Contribution to the production and use of biomass-derived solvents – a review

In this review key processes for the synthesis of greener or more sustainable solvents derived from renewable sources (saccharides, lignocellulose and triglycerides) are discussed. It is shown that a series of platform chemicals such as glycerol, levulinic acid and furans can be converted into a variety of solvents through catalytic transformations that include hydrolysis, esterification, reduction and etherification reactions. It was also considered several aspects of each class of solvent regarding performance within the context of the reactions or extractions for which it is employed.

Lipase-catalysed polycondensation of levulinic acid derived diol-diamide monomers: access to new poly(ester-co-amide)s

A new family of biobased poly(ester-co-amide)s is reported from the enzymatic polycondensation of a library of levulinic acid derived diol-diamide monomers with diesters.

Room-Temperature Asymmetric Transfer Hydrogenation of Biomass-Derived Levulinic Acid to Optically Pure γ-Valerolactone Using a Ruthenium Catalyst

This study presents a first report on ruthenium-catalyzed asymmetric transfer hydrogenation (ATH) of levulinic acid (LA) to chiral γ-valerolactone (GVL). ATH of LA has been explored with Noyori's chiral catalyst (Ru-TsDPEN) in methanol solvent. Efficacy of ATH reaction of LA was investigated under different reactions conditions such as temperature, catalyst, and hydrogen donor concentration. The effect of various organic tertiary bases along with formic acid (FA) as a hydrogen donor was studied, and N-methylpiperidine with FA (1:1 molar ratio) was revealed as an efficient hydrogen donor for ATH of LA to GVL furnishing chiral GVL with complete conversion and 93% enantiomeric excess (ee). This operationally simple and mild ATH protocol was tested for practical applicability of ATH of LA obtained from biomass waste (rice husk and wheat straw) and furnished chiral GVL with 82% ee.

Regio- and Enantio-selective Chemo-enzymatic C-H-Lactonization of Decanoic Acid to (S)-δ-Decalactone

The conversion of saturated fatty acids to high value chiral hydroxy-acids and lactones poses a number of synthetic challenges: the activation of unreactive C-H bonds and the need for regio- and stereoselectivity. Here the first example of a wild-type cytochrome P450 monooxygenase (CYP116B46 from Tepidiphilus thermophilus) capable of enantio- and regioselective C5 hydroxylation of decanoic acid 1 to (S)-5-hydroxydecanoic acid 2 is reported. Subsequent lactonization yields (S)-δ-decalactone 3, a high value fragrance compound, with greater than 90 % ee. Docking studies provide a rationale for the high regio- and enantioselectivity of the reaction.

Biocatalytic synthesis of lactones and lactams

Cyclic esters and amides (lactones and lactams) are important active ingredients and polymer building blocks. In recent years, numerous biocatalytic methods for their preparation have been developed including enzymatic and chemoenzymatic Baeyer-Villiger oxidations, oxidative lactonisation of diols, and reductive lactonisation and lactamisation of ketoesters. The current state of the art of these methods is reviewed.

Activity prediction of substrates in NADH-dependent carbonyl reductase by docking requires catalytic constraints and charge parameterization of catalytic zinc environment

Molecular docking of substrates is more challenging compared to inhibitors as the reaction mechanism has to be considered. This becomes more pronounced for zinc-dependent enzymes since the coordination state of the catalytic zinc ion is of greater importance. In order to develop a predictive substrate docking protocol, we have performed molecular docking studies of diketone substrates using the catalytic state of carbonyl reductase 2 from Candida parapsilosis (CPCR2). Different docking protocols using two docking methods (AutoDock Vina and AutoDock4.2) with two different sets of atomic charges (AM1-BCC and HF-RESP) for catalytic zinc environment and substrates as well as two sets of vdW parameters for zinc ion were examined. We have selected the catalytic binding pose of each substrate by applying mechanism based distance criteria. To compare the performance of the docking protocols, the correlation plots for the binding energies of these catalytic poses were obtained against experimental Vmax values of the 11 diketone substrates for CPCR2. The best correlation of 0.73 was achieved with AutoDock4.2 while treating catalytic zinc ion in optimized non-bonded (NBopt) state with +1.01 charge on the zinc ion, compared to 0.36 in non-bonded (+2.00 charge on the zinc ion) state. These results indicate the importance of catalytic constraints and charge parameterization of catalytic zinc environment for the prediction of substrate activity in zinc-dependent enzymes by molecular docking. The developed predictive docking protocol described here is in principle generally applicable for the efficient in silico substrate spectra characterization of zinc-dependent ADH.