Tetrahedron report number 203

Different types of microbiological transformation of steroids are reviewed, with special attention given to bioconversions applied in the manufacturing of steroid hormones, i.e., 11 alpha- 11 beta-, 16 alpha-, 17 alpha-hydroxylations and 1-dehydrogenation. Availability and utilization of raw materials for industrial production of steroids of the estrane, androstane, and pregnane series are discussed. Among the current trends in steroid research of a practical nature, immobilization of enzymes and living cells and the spore process are emphasized as alternative techniques of steroid transformation of possible future importance. Efforts to recognize, in cell-free preparations, the components of steroid-transforming enzyme systems as well as the cellular mechanisms of control of their biosynthesis and activity are described in order to illustrate the main subjects of current basic investigation in steroid bioconversion.

Biotransformations of steroids.

https://www.tandfonline.com/doi/pdf/10.1080/02648725.1987.10647842

Biocatalysis with immobilized cells

Although many microbial processes have been described which are able to produce interesting aroma compounds, the number of industrial applications are limited. Reasons for this are in most cases low final product yield, low biotransformation rates, substrates and/or end-products inhibition, toxicity towards the microorganisms themselves and difficulties of recovery from the bioreaction mixture. This means that the development of specific catalysts and processes is an important challenge for researchers in this field. This review presents two special kinds of catalysts, fungal spores and immobilized cells, with emphasis on their production and on their use in the production of aroma compounds. The production of fungal spores by solid state fermentation is described in greater detail. In the second part, this review also offers examples of development of three production processes, the production of methyl ketones of spores of Penicillium roquefortii, the hydroxylation of β-ionone by immobilized Aspergillus niger cells, and the production of alkyl pyrazines by bacterial in liquid and solid media. For each of these processes, the analysis of limiting steps—biological and/or physico-chemical—is presented and the significant role of process conditions to increase aroma yield is discussed.

Special transformation processes using fungal spores and immobilized cells.

Immobilization of Saccharomyces cerevisiae ATCC 834 within alginate beads enhances microbiological conversion of benzaldehyde to L-phenylacetyl carbinol (L-PAC), a precursor employed for synthesis of L-ephedrine. Yields of 90% L-PAC on benzaldehyde (initially 0.6% in medium) were obtained with immobilized cells, in contrast to about 10% with free cells which tend to form pellets in the presence of benzaldehyde. The predominant favorable action of immobilization appears to be a reduction in the toxic or inhibitory effects of benzaldehyde. With an initial benzaldehyde concentration of about 0.6% in the medium the optimum cell mass concentration was observed to be about 28 g cell mass (immobilized) per liter of medium.

Production of L-phenylacetyl carbinol by immobilized yeast cells. I. Batch fermentation

Hydroxylation in the 11 alpha-position in the progesterone molecule employing immobilized spores of Aspergillus ochraceus strain No. G8 (CDRI catalogue No.) was achieved. For immobilization the activity of the spores was evaluated on a variety of matrices such as alginate beads, epoxy resin beads, polyacrylamide gel, and collagen. Spores entrapped in polyacrylamide gel were found to be the most active. Studies of various parameters, e.g. monomer content, cell loading capacity, optimum pH, temperature, and substrate concentration, were carried out on polyacrylamide gel. In polyacrylamide, the entrapped spores normal decay pattern, as indicated by loss of activity, was observed after four uses. At the end of 15 cycles, the residual activity was found to be 18% of the original. It was possible to regenerate the activity by incubating the preparation in a nutrient medium. The regenerated spores showed increasing rate of loss of activity upon recycling.

Studies on immobilized fungal spores for microbial transformation of steroids: 11 α‐Hydroxylation of progesterone with immobilized spores of Aspergillus ochraceus G8 on polyacrylamide gel and other matrices

P. P. Goswami

Papers

Studies on immobilized fungal spores for microbial transformation of steroids: 11 α‐Hydroxylation of progesterone with immobilized spores of Aspergillus ochraceus G8 on polyacrylamide gel and other matrices