Search

Agricultural crops provide a considerable reservoir of useful and low cost raw materials like fats and oils, plant proteins and carbohydrates. By selective combination of their molecular constituents (e. g. fatty acids, glycerol, amino acids, saccharides), a wide variety of surface active materials can be prepared. Due to their molecular constitution, all of them are potentially biodegradable. In this article we describe two generally applicable methods for the synthesis of such combination products using fatty acids from plant oils – one of the most important renewable materials as feedstock for the chemical industry – in combination with amino acids and monosaccharides including sugar alcohols. Using the high selectivities displayed by lipases, which catalyze a wide variety of transformations under very mild conditions (pH, temperature) with high atom efficiency in various non-toxic solvents and without the production of by-products or waste, numerous useful products can be obtained ranging all the way from surface active compounds (detergents and emulsifiers for food and personal care products) such as mono- and diglycerides, sugar esters, synthetic building blocks, products for food and dietary applications, all the way to novel methods for the production of biofuels (biodiesel). In our continuing effort to devise novel and generally applicable methods for the syntheses of such combination products we recently discovered a novel class of building blocks, fatty acid modified anhydrides of hydroxy carboxylic acids such as citric acid, tartaric acid and malic acid which led to alternative synthetic approaches towards new classes of the title compounds.

The protease from Bacillus licheniformis (alcalase) shows a remarkable broad substrate tolerance and high enantioselectivity against nonproteinogenic racemic amino acid derivatives. N-acetyl protected amino acid esters of mono-, di- or tri-substituted phenyl alanines and even tert.-leucine were hydrolyzed with high enantioselectivity. The obtained mixtures of (S)-N-acetyl amino acid and (R)-N-acetyl amino acid ester can easily be separated. The R- or S-amino acids were obtained by acidic cleavage of the optically pure derivatives or the (R)-ester was racemized by treatment with potassium t-butylate.

Publisher Summary This chapter summarizes important types of screening experiments commonly to be executed in laboratories engaged in the synthetic applications of lipases. Faced with the necessity of finding the most suitable lipase for the solution of a synthetic problem, organic chemists usually have to address one of the following: (1) adopting an “established” lipase with known selectivities and substrate tolerance toward the transformation of a given substrate; (2) finding the best lipase among commercially available enzymes for the conversion of a given target molecule; (3)finding a new lipase for the conversion of a defined target molecule; and (4) most likely of interest mainly to enzyme producers and in an attempt to make new lipases with interesting properties available to the scientific community, screening lipases—or microorganisms producing such enzymes—for their substrate tolerance, enantioselectivity, solvent dependence, and other properties. The chapter aims to inform the important issues related to the application of these enzymes.

Publisher Summary Lipases are probably at present the most widely used biocatalysts in organic synthesis. Many of them are commercially available, they are frequently stable toward elevated temperatures and organic solvents, and they are easy to handle. Due to their high enantio- and regioselectivities, broad substrate tolerance and versatility in catalyzing both hydrolyses and esterifications, these enzymes have developed in the last decade into high efficient tools in the hands of the organic chemist. With the main focus on lipase-catalyzed esterifications via acyl transfer (transesterification), this chapter describes numerous examples for such reactions as applied to a wide variety of structurally different hydroxy compounds. The examples range from the preparation of enantiomerically pure molecules via kinetic resolutions and enantiotope differentiations, respectively, all the way to regioselective functionalizations of natural products, such as carbohydrates and nucleosides.

(1 R ,2 S )- and (1 S ,2 R )-Acetoxycycloalkanedimethanols 1-6 of high enantiomeric purities were prepared by enzymatic hydrolysis and esterification respectively in presence of lipase from porcine pancreas (PPL) and Pseudomonas sp . (SAM-II).

Bicyclo[2.2.1]heptene derivatives (1)–(3), building blocks for terpenoid natural products, have been prepared with high enantiometric purities by enzymatic hydrolysis of their racemic esters in the presence of porcine liver esterase (PLE) and an ester hydrolase from Pseudomonas sp. (SAM-II).

Bicyclo[2.2.1]heptene derivatives (1)–(3), building blocks for terpenoid natural products, have been prepared with high enantiometric purities by enzymatic hydrolysis of their racemic esters in the presence of porcine liver esterase (PLE) and an ester hydrolase from Pseudomonas sp. (SAM-II).

(1 R ,2 S )- and (1 S ,2 R )-Acetoxycycloalkanedimethanols 1-6 of high enantiomeric purities were prepared by enzymatic hydrolysis and esterification respectively in presence of lipase from porcine pancreas (PPL) and Pseudomonas sp . (SAM-II).