Appl Microbiol Biotechnol (2010) 85:893–899 Fig. 4 Natural and engineered reactions catalyzed by the leucine biosynthetic operon, leuABCD. 2KV 2-ketovalerate, 2KC 2-ketocaproate, PrOH 1-propanol, BuOH 1-butanol, 3MB 3-methyl-1-butanol iBuOH 3MB Natural Engineered KIV KIC AceCoA 2KB 2KV 2KC 897 PrOH BuOH triglycerides into a diesel fuel (Gerpen 2005). However, longer chain alcohols, like pentanols, are readily used in the esterification reaction and can be preferable due to their greater fat solubility as compared to methanol (Salis et al. 2005). Another potential fuel application for pentanols and other higher alcohols could come from their polymerization to longer compounds suitable for diesel, jet fuel, or other fuels (Marchionna et al. 2001). Through a simple chemical activation of the hydroxyl group to a carbon–carbon double bond, these alcohols could be converted to a wide range of useful hydrocarbons. Besides diesel esters, pentanols can form other esters for more applications. One of the primary flavor esters found in food fermentations is isoamyl acetate, which comes from the reaction of 3-methyl-1-butanol and acetyl-CoA. Recent work has demonstrated the viability of engineering E. coli for the production of isoamyl acetate from added 3-methyl- 1-butanol by expressing genes from S. cerevisiae (Vadali et al. 2004). Other work has demonstrated the potential to combine ethanol production with simultaneous expression of esterification enzymes for in vivo biodiesel production (Kalscheuer et al. 2006). This suggests that the endogenous production of 3-methyl-1-butanol demonstrated in E. coli (Connor and Liao 2008) could be combined with genes for its esterification with acetyl-CoA for engineering of the direct production of isoamyl acetate in E. coli. A product used in the mining industry, amyl xanthate, is another useful pentanol ester. Amyl xanthate can come from any of the primary pentanol isomers, e.g., 1-pentanol, 2-methyl-1-butanol (The Dow Chemical Company 2002c; 1-Pentanol Lappe and Hofmann 2005). Pentanol isomers are often used as solvents for chemical reaction, liquid extraction, and products such as paint and coatings (The Dow Chemical Company 2002a, b, c; Lappe and Hofmann 2005). They are especially useful as chemical intermediates or starting materials for a wide variety of products, including pharmaceuticals, antioxidants, cosmetics, herbicides, liquid crystals, dyes, flavorings, and catalysts (Gershanovskii et al. 1973; The Dow Chemical Company 2002a, b, c; Lappe and Hofmann 2005). Other applications for pentanols are additives for lubrication oil, corrosion inhibitors, and plasticizers and stabilizers for polymer plastics (The Dow Chemical Company 2002b, c; Lappe and Hofmann 2005). Table 1 Summary of highest titers and yields for engineered pentanol production Pentanol Titer (g/L) Yield (g/g) Reference 2-Methyl-1-butanol 1.25 0.37 0.25 3-Methyl-1-butanol 1.28 0.41 0.28 1-Pentanol 0.75 0.08 Pentenol 0.11 0.17 N/Aa N/Aa 0.11 0.008 0.002 0.038 N/Aa 0.006 Cann and Liao 2008 Fukuda et al. 1993 Kielland-Brandt et al. 1979 Connor and Liao 2008 Watanabe et al. 1990 Suzzi et al. 1998 Zhang et al. 2008 Mauricio et al. 1997 Withers et al. 2007 Not able to be determined from available data