# Enzymatic Synthesis of Biobased Polyesters and Polyamides
## 4 Biobased Monomers for Polyester and Polyamide Synthesis
### Biobased Lactones and Lactans  
Lactones and lactams are abundant moieties in naturally occurring compounds with diversified structures and varied ring sizes. Examples of naturally occurred lactones and lactams are tetronic acid, 5,6-dihydropyran-2-one, coumarin, \(\alpha\)-alkylidene-\(\gamma\)-lactones and lactams, \(\alpha\)-alkylidene-\(\delta\)-lactones and lactams, \(\beta\)-lactam, and so on. They are widely applied in the fine and functional perfumery and in the pharmaceutical industry. However, few studies referred to the synthesis of polyesters and polyamides from naturally occurring lactones and lactams, probably due to their complicated structures, limited availability, and high price [77].  
3-Hydroxybutyrolactone (3-HBL) is a biobased platform molecules listed in \"DOE TOP 10\" [18]. It is a chiral compound that can be used for the synthesis of pharmaceuticals, polymers and organic solvents. However, the chemical synthesis of 3-HBL is quite difficult, with multiple steps [5; 18; 78]. Currently, (5)-3-HBL is commercially produced from L-malic acid via a continuous chemical synthesis process under high pressure in a fixed-bed reactor using a ruthenium-based catalyst [79; 80] This process involves hazardous conditions, expensive catalysts, as well as multiple purification steps [78].  
\begin{table}
\begin{tabular}{c c c c} \hline
**Biobased Polyamide** & **Biosourcing (\%) a** & **Manufacturer** & **Trademark** \\ \hline Nylon 4,10 (PA 4,10) & 100 & DSM (IEEE, The Netherlands) & EcoP\(\omega\)\(\Omega\)\(\Omega\)\(\Omega\)\(\Omega\) \\ \hline  & & BASF (Ludwigshafen, Germany) & Ultramid\({}^{\text{a}}\)\({}^{\text{b}}\) Balance \\  & & EMS-GRIVORY (Demat/Ems, Switzerland) & Grillamid\({}^{\text{b}}\)\({}^{\text{c}}\)\({}^{\text{b}}\)\({}^{\text{c}}\  
Recently, [PERSON] et al. [78; 81] developed a biosynthesis pathway for 3-HBL in recombinant _E. coli_ (_Escherichia coli_) using glycolic acid or glucose as the starting material. However, the large-scale biological production of 3-HBL is still challenging, which requires further studies.  
Some other lactones, such as propiolactone, \(\gamma\)-butylrolactone, angellactone, \(\gamma\)-valerolactone, and furan-2(5H)-one, can be derived from renewable resources [18; 82].  
In addition, lactams can be converted from biomass feedstocks. Among them, \(\varepsilon\)-caprolactam is an important raw material for the synthesis of nylon 6. At present, \(\varepsilon\)-caprolactam is produced via a six-step chemical process using benzene and ammonia as starting materials. Recently [PERSON] et al. [83] reported the conversion of biobased 5-(hydroxymethyl)furfurral (HMF) to \(\varepsilon\)-caprolactam via four steps (Scheme 3), two steps less than the traditional approach. In addition, [PERSON] et al. [84] reported the production of \(\varepsilon\)-caprolactam from biobased levulinic acid via a four-step process. Moreover, synthesis of \(\varepsilon\)-caprolactam from sugar-derived lysine is developed [85; 86]. It is also possible to produce \(\varepsilon\)-caprolactam via fermentation of sugars and the relevant industrial process is currently under development [31].