Biotransformation of 3-keto-androstanes by Gongronella butleri VKM F-1033

Identification of a Gene Encoding a New Fungal Steroid 7-Hydroxylase and Its Functional Characterization in Pichia pastoris Yeast

The hydroxylation of steroids in the C7β position is one of the rare reactions that allow the production of value-added precursors in the synthesis of ursodeoxycholic acid and other pharmaceuticals. Recently, we discovered this activity in the ascomycete Curvularia sp. VKM F-3040. In this study, the novel gene of 7-hydroxylase (P450cur) was identified as being heterologously expressed and functionally characterized in Pichia pastoris. Transcriptome data mining and differential expression analysis revealed that 12 putative genes in Curvularia sp. mycelia significantly increased their expression in response to dehydroepiandrosterone (DHEA). The transcriptional level of the most up-regulated cytochrome P450cur gene was increased more than 300-fold. A two-gene construct with a candidate P450cur gene and the gene of its natural redox partner, NADPH-cytochrome P450 reductase (CPR), which is interconnected by a T2A element, was created. Using this construct, recombinant P. pastoris strains co-expressing fungal P450cur and CPR genes were obtained. The functional activity of the recombinant P450cur was studied in vivo during the bioconversion of androstane steroids. The fungal 7-monooxygenase predominantly catalyzed the 7β-hydroxylation of androstadienedione (ADD), DHEA, and androstenediol, whereas 1-dehydrotestosterone was hydroxylated by P450cur mainly at the C7-Hα position. To our knowledge, this is the first report of a recombinant yeast capable of catalyzing the 7α/β-hydroxylation of ADD and DHEA.

Bioconversion of Phytosterols into Androstenedione by Mycolicibacterium

The chapter describes the bioconversion of phytosterols into androstenedione (AD) by Mycolicibacterium spp. in shake flasks and fermenters, as well as LC-MS-based methods for analysis of phytosterols and steroid products. Phytosterols are derived as by-products of vegetable oil refining and manufacture of wood pulp. They contain the same four-ring nucleus as steroids and may be converted to high-value steroids by removing the sidechain at C17 and minor changes at other sites in the ring structure. Many bacteria, including Mycolicibacterium spp., can degrade phytosterols. Mutants of Mycolicibacterium spp. unable of ring cleavage can, when growing on phytosterols, accumulate the steroid intermediates androstenedione (AD) and androstadienedione (ADD). The practical challenge with microbial conversion of phytosterols to steroids is that both the substrate and the product are virtually insoluble in water. In addition, some steroids, notably ADD, may be toxic for the cells. Two main strategies have been employed to overcome this challenge: the use of two-phase systems and the addition of chemically modified cyclodextrins. The latter method is used here. Defined cultivation and bioconversion media for both shake flask and fermenter are given, as well as hints how to minimize the practical problems due to the water-insoluble phytosterol. Sampling, sample extraction, and quantification of substrates and products using LC-MS analysis are described.

Ursodeoxycholic acid production by Gibberella zeae mutants

Ursodeoxycholic acid (UDCA) is a highly demanded pharmaceutical steroid widely used in medicine. An ascomycete Gibberella zeae VKM F-2600 is capable of producing UDCA by 7β-hydroxylation of lithocholic acid (LCA). The present study is aimed at the improvement of the fungus productivity. The original procedures for the protoplast obtaining followed by UV mutagenesis and screening of ketoconazole-resistant mutant clones have been applied. The highest yield of G. zeae protoplasts was obtained when using the mycelium in the active growth phase, ammonium chloride as an osmotic stabilizer and treatment of the fungal cells by the lytic enzymes cocktail from Trichoderma hurzanium. The conditions for effective protoplast regeneration and the UV-mutagenesis were found to provide 6–12% survival rate of the protoplasts with superior number of possible mutations. Three of 27 ketoconazole-resistant mutant clones obtained have been selected due to their increased biocatalytic activity towards LCA. The mutant G. zeae M23 produced 26% more UDCA even at relatively high LCA concentration (4 g/L) as compared with parent fungal strain, and the conversion reached 88% (w/w). The yield of UDCA reached in this study prefers those ever reported. The results contribute to the knowledge on ascomycete mutagenesis, and are of importance for biotechnological production of value added cholic acids.

Efficient procedures for production and regeneration of Gibberella zeae protoplasts were determined.

Fungal mutants were obtained with elevated 7β-hydroxylase activity.

Mutant G. zeae M23 almost fully converts LCA (4 g/L) to UDCA.

Draft genome of Gongronella butleri reveals the genes contributing to its biodegradation potential

BACKGROUND

Gongronella butleri is a fungus with many industrial applications including the composting of solid biowaste. Kerala Agricultural University, India, has developed a microbial consortium of which GbKAU strain of G. butleri is a major component. Even with great industrial significance, genome of this fungus is not published, and the genes and pathways contributing to the applications are not understood. This study had the objective to demonstrate the solid biowaste decomposing capability of the strain, to sequence and annotate the genome, and to reveal the genes and pathways contributing to its biodegradation potential.

RESULTS

Strain GbKAU of G. butleri isolated and purified from the organic compost was found to produce higher levels of laccase and amylase, compared to Bacillus subtilis which is being widely used in biosolid waste management. Both were shown to be equally efficient in the in vivo composting capabilities. Whole genome sequencing has given ~11 million paired-end good quality reads. De novo assembly using dual-fold approach has yielded 44,639 scaffolds with draft genome size of 29.8 Mb. A total of 11,428 genes were predicted and classified into 359 groups involved in diverse pathways, of which 14 belonged to the enzymes involved in the degradation of macromolecules. Seven previously sequenced strains of the fungus were assembled and annotated. A direct comparison showed that the number of genes present in those strains was comparable to our strain, while all the important biodegrading genes were conserved across the genomes. Gene Ontology analysis had classified the genes according to their molecular function, biological process, and cellular component. A total of 104,718 SSRs were mined and classified to mono- to hexa-nucleotide repeats. The variant analysis in comparison with the closely related genus Cunninghamella has revealed 1156 variants.

CONCLUSIONS

Apart from demonstrating the biodegradation capabilities of the GbKAU strain of G. butleri, the genome of this industrially important fungus was sequenced, de novo assembled, and annotated. GO analysis has classified the genes based on their functions, and the genes involved in biodegradation were revealed. Biodegradation potential, genome features in comparison with other strains, and the functions of the identified genes are discussed.

Hydroxylation of pregnenolone and dehydroepiandrosterone by zygomycete Backusella lamprospora VKM F-944: selective production of 7α-OH-DHEA

In this paper, we studied the transformation of two 3β-hydroxy-5-ene-steroids-pregnenolone and dehydroepiandrosterone (DHEA) by Backusella lamprospora VKM F- 944. The soil-dwelling zygomycete wild-type strain has been earlier selected during the screening and previously unexplored for this purpose. The fungus fully converted pregnenolone to form a mixture of axial 7α-hydroxy-pregnenolone and 7α,11α-dihydroxy-pregnenolone, while no metabolites with β-orientation of the hydroxyl group were detected. The pathway to 7α,11α-diOH-pregnenolone seems to include 7α-hydroxylation of 11α-hydroxylated derivative. The only product from DHEA was identified as 7α-hydroxy-DHEA. The structures of steroid metabolites were confirmed by HPLC, mass-spectrometry (MS), and ¹H and ¹³C NMR analyses. Under the optimized conditions, the yield of 7α-OH-DHEA reached 94% (w/w) or over 14 g/L in absolute terms, even at high concentration of the substrate (DHEA) (15 g/L). To our knowledge, it is the highest yield of the value-added 7α-OH-DHEA reported so far. The results contribute to the knowledge of the diversity of the wild-type fungal strains capable of effective steroid hydroxylation. They could be applied for the production of allylic steroid 7α-alcohols that are widely used in medicine. KEY POINTS: • Zygomycete Backusella lamprospora actively hydroxylates 3β-hydroxy-5-en-steroids. • Axial 7α-hydroxylation is the preferable reaction by the strain towards pregnenolone and DHEA. • The strain selectively produces 7α-OH-DHEA even at high substrate concentrations (up to 15 g/L).

Steroid modification by filamentous fungus Drechslera sp.: Focus on 7-hydroxylase and 17β-hydroxysteroid dehydrogenase activities

Fungal strain Drechslera sp. Ph F-34 was shown to modify 3-oxo- and 3-hydroxy steroids of androstane series to form the corresponding allylic 7-alcohols and 17β-reduced derivatives thus evidencing the presence of 7α-, 7β-hydroxylase and 17β-hydroxysteroid dehydrogenase (17β-HSD) activities. The growing mycelium predominantly hydroxylated androsta-1,4-diene-3,17-dione (ADD) at the 7β-position, while much lower 7α-hydroxylation was observed. Along with 7β-hydroxy-ADD and its corresponding 7α-isomer, their respective 17β-alcohols were produced. In this study, transformation of ADD, androst-4-en-17β-ol-3-one (testosterone, TS) and 3β-hydroxyandrost-5-en-17-one (dehydroepiandrosterone, DHEA) by resting mycelium of Drechslera sp. have been estimated in different conditions with regard to the inducibility and functionality of the 17β-HSD and 7-hydroxylase enzyme systems. Steroids of androstane, pregnane and cholane series were evaluated as inducers. The inhibitory analysis was provided using cycloheximide (CHX). Steroids were assayed using TLC and HPLC methods, and the structures were confirmed by mass-spectrometry, ¹H and ¹³C NMR spectroscopy data. 17β-HSD of the mycelium constitutively reduced 17-carbonyl group of ADD and DHEA to form the corresponding 17β-alcohols, namely, androsta-1,4-diene-17β-ol-3-one (1-dehydro-TS), and androst-5-ene-3β,17β-diol. Production of the 7α- and 7β-hydroxylated derivatives depended on the induction conditions. The inducer effect relied on the steroid structure and decreased in the order: DHEA > pregnenolone > lithocholic acid. β-Sitosterol did not induce hydroxylase activity in Drechslera sp. CHX fully inhibited the synthesis of 7-hydroxylase in Drechslera mycelium thus providing selective 17-keto reduction. Results contribute to the diversity of steroid modifying enzymes in fungi and can be used at the development of novel biocatalysts for production of valuable steroid 7(α/β)- and 17β-alcohols.

Modulating the active site lid of an alcohol dehydrogenase from Ralstonia sp. enabled efficient stereospecific synthesis of 17β-hydroxysteroids

Enzymatic stereospecific reduction of 17-oxosteroids offers an attractive approach to access 17β-hydroxysteroids of pharmaceutical importance. In this study, by adjusting the flexibility of α6-helix at the substrate entrance of the alcohol dehydrogenase from Ralstonia sp. (RasADH), the catalytic activity toward the stereospecific 17β-reduction of androstenedione was improved without sacrifice of the enantioselectivity. Among the mutants, F205I and F205A exhibited up to 623- and 523-fold improvement in catalytic efficiency, respectively, towards a range of different 17-oxosteroids compared to the wild-type enzyme. The corresponding 17β-hydroxysteroids were prepared in optically pure form with high space-time productivity and isolated yields using F205I as the biocatalyst, indicating that these mutants are promising biocatalysts for this useful transformation. These results suggest that modulating the flexibility of the active site lid offers an effective approach to engineer alcohol dehydrogenase for accommodating bulky steroidal substrates.

Identification and Immobilization of an Invertase With High Specific Activity and Sucrose Tolerance Ability of Gongronella sp. w5 for High Fructose Syrup Preparation

Invertases catalyze the hydrolysis of sucrose into fructose and glucose and can be employed as an alternative in producing high fructose syrup. In this study, we reported the heterologous expression of an invertase gene (GspInv) of Gongronella sp. w5 in Komagataella pastoris. GspInv activity reached 147.6 ± 0.4 U/mL after 5 days of methanol induction. GspInv is invertase with a high specific activity of 2,776.1 ± 124.2 U/mg toward sucrose. GspInv showed high tolerance to sucrose (IC 5 0 = 1.2 M), glucose (IC 5 0 > 2 M), fructose (IC 5 0 = 1.5 M), and a variety of metal ions that make it an ideal candidate for high fructose syrup production. A carbohydrate-binding module was sequence-optimized and fused to the N-terminus of GspInv. The fusion protein had the highest immobilization efficiency at room temperature within 1 h adsorption, with 1 g of cellulose absorption up to 8,000 U protein. The cellulose-immobilized fusion protein retained the unique properties of GspInv. When applied in high fructose syrup preparation by using 1 M sucrose as the substrate, the sucrose conversion efficiency of the fused protein remained at approximately 95% after 50 h of continuous hydrolysis on a packed bed reactor. The fused protein can also hydrolyze completely the sucrose in sugarcane molasses. Our results suggest that GspInv is an unusual invertase and a promising candidate for high fructose syrup preparation.

Two new 23S,26R-hydroxylated spirostanoid saponins from the fruits of Solanum indicum var. recurvatum

Solanum indicum var. recurvatum, distributed mainly in Hekou, Simao and Menghai areas of Yunnan province, China, is characterized by stellate pubescent leaves with irregular lengths and oblong, short, and downwardly curved anthers. The original species, S. indicum, has been used as an anti-inflammatory, wound-healing agent, an analgesic, and for the treatment of rhinitis, cough, and breast cancer in Chinese folk medicine. The variety was chemically studied for the first time, leading to the isolation of two new rare 23S,26R-hydroxylated spirostanoid saponins, together with five known steroidal components, two of which the rare natural ketosteroids 6-hydroxyandrosta-1,4-diene-3,17-dione and rostadienedione have been isolated from the genus Solanum for the first time. Elucidation of the structures was accomplished by extensive 1D and 2D NMR, UV, and HRESIMS spectroscopic methods.

Biotransformation of androstenedione and androstadienedione by selected Ascomycota and Zygomycota fungal strains

Filamentous fungi is a huge phylum of lower eukaryotes with diverse activities towards various substrates, however, their biocatalytic potential towards steroids remains greatly underestimated. In this study, more than forty Ascomycota and Zygomycota fungal strains of 23 different genera were screened for the ability to catalyze structural modifications of 3-oxo-androstane steroids, - androst-4-ene-3,17-dione (AD) and androsta-1,4-diene-3,17-dione (ADD). Previously unexplored for these purposes strains of Absidia, Acremonium, Beauveria, Cunninghamella, Doratomyces, Drechslera, Fusarium, Gibberella genera were revealed capable of producing in a good yield valuable 7α-, 7β-, 11α- and 14α-hydroxylated derivatives, as well as 17β-reduced and 1(2)-dehydrogenated androstanes. The bioconversion routes of AD and ADD were proposed based on the key intermediates identification and time courses of the bioprocesses. Six ascomycete strains were discovered to provide effective 7β-hydroxylation of ADD which has not been so far reported. The structures of major products and intermediates were confirmed by HPLC, mass-spectrometry (MS), ¹H and ¹³C NMR analyses. The results contribute to the knowledge on the functional diversity of steroid-transforming filamentous fungi. Previously unexplored fungal biocatalysts capable of effective performing structural modification of AD and ADD can be applied for industrial bioprocesses of new generation.

Production of 14α-hydroxysteroids by a recombinant Saccharomyces cerevisiae biocatalyst expressing of a fungal steroid 14α-hydroxylation system

The 14α-hydroxysteroids have specific anti-gonadotropic and carcinolytic biological activities and can be produced by microbial biotransformation. The steroid 11β-/14α-hydroxylase P-450_lun from Cochliobolus lunatus is the only fungal cytochrome P450 enzyme identified to date with steroid C14 hydroxylation ability. Previous work has mainly revealed the 11β-hydroxylation activity of the P-450_lun towards cortexolone (RSS) substrate; however, the potential steroid 14α-hydroxylation activity of this enzyme, especially for androstenedione (AD) substrate, has not yet conducted in-depth testing. In this work, we further tested the steroid 14α-hydroxylation activity of the P-450_lun towards RSS and AD in the Saccharomyces cerevisiae system. We demonstrated that P-450_lun functions as the specific 14α-hydroxylase towards the AD substrate (regiospecificity > 99%); however, it showed a poor C14-hydroxylation regiospecificity (around 40%) for the RSS substrate. In addition, through transcriptome analysis combined with gene functional characterizations, we also identified and cloned the gene for the P-450_lun-associated redox partner CPR_lun. Finally, through codon optimization, knockout of genes for the side reactions related enzymes GCY1 and YPR1, and increasing copies of the P-450_lun and CPR_lun, we developed a recombinant S. cerevisiae biocatalyst based on the C. lunatus steroid 14α-hydroxylation system to produce 14α-hydroxysteroids. Initial production of 14α-OH-AD (150 mg/L day productivity, 99% regioisomeric purity, and 60% w/w yield) and 14α-OH-RSS (64 mg/L day productivity, 40% regioisomeric purity, and 26% w/w yield) were separately achieved in shake flasks; these results represent the highest level of 14α-hydroxysteroid production in the current yeast system.

Immobilized and Free Cells of Geotrichum candidum for Asymmetric Reduction of Ketones: Stability and Recyclability

Marine-derived fungus Geotrichum candidum AS 2.361 was previously reported by our group as an active strain for the enantioselective reduction of ketones. Although some other Geotrichum strains were also found from the terrestrial sources, information on their stability and reusability is scarce. Herein, the stabilities—in terms of pH tolerance, thermostability, and storage stability, and reusability—of G. candidum AS 2.361 were described for the asymmetric reduction of a series of aromatic ketones. Two differently immobilized cells (agar immobilization and calcium alginate immobilization) as well as free cells were prepared. For three substrates (1-(3-bromophenyl) ethan-1-one (1b), 1-(2-chlorophenyl) ethan-1-one (1d), and acetophenone (1g)) immobilized cells on agar showed a great improvement in the bioreduction activities compared to the free cells, increasing yields up to 97% with ee values of 99%. Cells immobilized on agar/calcium alginate could maintain more than 90% of the original activities within the assayed pH ranges of 3.5–11, while free cells were highly sensitive to alkaline and acidic conditions. Concerning thermostability, immobilized cells on agar kept 99% of their original activities after incubation at 60 °C for 1 h, while almost no activity was detected for the free cells under the same condition. Immobilized cells were stable at 4 °C for 80 days without any activity loss, while free cells started to decrease the activity after storage at 4 °C for six days. The immobilized cells retained almost 99% activity after four reuse cycles, while free cells lost almost all the activities at on the third cycle.

Biocatalyst-mediated production of 11,15-dihydroxy derivatives of androst-1,4-dien-3,17-dione

Hydroxylation of steroids at various positions is a powerful tool for the production of valuable pharmaceutical ingredients and precursors. Our paper reported the synchronous dihydroxylation of an efficient strain, i.e., Colletotrichum lini AS3.4486, at two points. C. lini AS3.4486 was selected from 10 strains; this strain can catalyze the dihydroxylation of androst-1,4-dien-3,17-dione at C-11α and C-15α positions. Transformation of ADD(I) by C. lini AS3.4486 produced metabolites II-IV. The structures of these compounds were elucidated by liquid chromatography-mass spectrometry (LC-MS), Fourier Transform infrared spectroscopy (FTIR), nuclear magnetic resonance (NMR), and X-ray as 15-hydroxyandrost-1,4-dien-3,17-dione (15α-OH-ADD; II), 11,15-dihydroxyandrost-1,4-dien-3,17-dione (11,15-diOH-ADD; III), and 15,17β-dihy-droxyandrost-1,4-dien-3-one (15-OH-BD; BD is the abbreviation of boldenone; IV). III, as a novel compound, was reported for the first time. The course of conversion and mechanism about dihydroxylation reaction was also investigated. On the basis of time course analysis of hydroxylation, I underwent regioselective hydroxylation at 15 position and was subsequently converted to III and IV. Enzyme inhibition analysis showed that 11- and 15-hydroxylations were catalyzed by different hydroxylases. The effect of substrate concentration on I transformation was also determined. Results showed that the optimum concentration of I was 20 g/L, and the yield of III was up to 18.8 g/L.

Bioconversion of Phytosterols into Androstenedione by Mycobacterium

The chapter describes the bioconversion of phytosterols to androstenedione (AD) with Mycobacterium spp. in shake flasks and fermenters, as well as LC-MS based methods for analysis of phytosterols and steroid products.Phytosterols are derived as a by-product of vegetable oil refining and of manufacture of wood pulp. Phytosterols contain the same four-ring nucleus as steroids, and may be converted to high-value steroids by removing the side chain at C17 and minor changes at other sites in the ring structure.Many bacteria, including Mycobacterium spp., are able to degrade phytosterols. Mutants of Mycobacterium spp. unable of ring cleavage can, when growing on phytosterols, accumulate the steroid intermediates androstenedione (AD) and/or androstadienedione (ADD).The practical challenge with microbial conversion of phytosterols to steroids is that both the substrate and the product are virtually insoluble in water. In addition, some steroids, notably ADD, may be toxic to cells.Two main strategies have been employed to overcome this challenge: the use of two-phase systems, and the addition of chemically modified cyclodextrins. The latter method is used here.Defined cultivation and bioconversion media for both shake flask and fermenter are given, as well as suggestions to minimize the practical problems caused by the water-insoluble phytosterol. Sampling, sample extraction, and quantification of substrates and products using LC-MS analysis are described.

Research on Biochemical Materials with Hydroxylation of Androst-4-en-3,17-dione by Colletotrichum lini AS3. 4486

Microbial transformation of androst-4-en-3,17-dione (AD; 1) usingColletotrichum liniAS3. 4486 resulted in the production of two metabolites 2 and 3. The structures of these compounds were elucidated by spectroscopic analysis (LC-MS, FTIR and NMR) as 15α-hydroxyandrost-4-en-3,17-dione (15α-OH-AD; 2) and 11α,15α-dihydroxyandrost-4-en-3,17-dione (11α,15α-diOH-AD; 3). AD underwent regioselective hydroxylation at 15α position, subsequently hydroxylated at 11α position and converted to compound 3. 11α,15α-diOH-AD as an important metabolic product was pharmaceutical intermediate and the yield was up to 97.58% when the concentration of substrate was 4 g L-1.

Immobilization of Acetobacter sp. CCTCC M209061 for efficient asymmetric reduction of ketones and biocatalyst recycling

Background

The bacterium Acetobacter sp. CCTCC M209061 is a promising whole-cell biocatalyst with exclusive anti-Prelog stereoselectivity for the reduction of prochiral ketones that can be used to make valuable chiral alcohols such as (R)-4-(trimethylsilyl)-3-butyn-2-ol. Although it has promising catalytic properties, its stability and reusability are relatively poor compared to other biocatalysts. Hence, we explored various materials for immobilizing the active cells, in order to improve the operational stability of biocatalyst.

Results

It was found that Ca-alginate give the best immobilized biocatalyst, which was then coated with chitosan to further improve its mechanical strength and swelling-resistance properties. Conditions were optimized for formation of reusable immobilized beads which can be used for repeated batch asymmetric reduction of 4′-chloroacetophenone. The optimized immobilized biocatalyst was very promising, with a specific activity of 85% that of the free-cell biocatalyst (34.66 μmol/min/g dw of cells for immobilized catalyst vs 40.54 μmol/min/g for free cells in the asymmetric reduction of 4′-chloroacetophenone). The immobilized cells showed better thermal stability, pH stability, solvent tolerance and storability compared with free cells. After 25 cycles reaction, the immobilized beads still retained >50% catalytic activity, which was 3.5 times higher than degree of retention of activity by free cells reused in a similar way. The cells could be recultured in the beads to regain full activity and perform a further 25 cycles of the reduction reaction. The external mass transfer resistances were negligible as deduced from Damkohler modulus Da < <1, and internal mass transfer restriction affected the reduction action but was not the principal rate-controlling step according to effectiveness factors η < 1 and Thiele modulus 0.3<∅ <1.

Conclusions

Ca-alginate coated with chitosan is a highly effective material for immobilization of Acetobacter sp. CCTCC M209061 cells for repeated use in the asymmetric reduction of ketones. Only a small cost in terms of the slightly lower catalytic activity compared to free cells could give highly practicable immobilized biocatalyst.

Microbial steroid transformations: current state and prospects

Studies of steroid modifications catalyzed by microbial whole cells represent a well-established research area in white biotechnology. Still, advances over the last decade in genetic and metabolic engineering, whole-cell biocatalysis in non-conventional media, and process monitoring raised research in this field to a new level. This review summarizes the data on microbial steroid conversion obtained since 2003. The key reactions of structural steroid functionalization by microorganisms are highlighted including sterol side-chain degradation, hydroxylation at various positions of the steroid core, and redox reactions. We also describe methods for enhancement of bioprocess productivity, selectivity of target reactions, and application of microbial transformations for production of valuable pharmaceutical ingredients and precursors. Challenges and prospects of whole-cell biocatalysis applications in steroid industry are discussed.

Follow-up of natural products isolation

Follow-up of natural products isolation refers to re-isolation of compound(s) of interest in larger amounts for further pharmacological testing, conclusive structure elucidation, structure modifications to synthesize analogs for structure-activity relationships (SAR) studies, preformulation and formulation studies or clinical trials. In addition to conventional synthetic chemistry approaches, several other methodologies can be applied for following-up natural products isolation. This chapter outlines, with specific examples, various strategies and methods involved in follow-up of natural products isolation.

11α,15α-Dihy-droxy-androst-4-ene-3,17-dione

The title compound, C(19)H(26)O(4), was biotransformed from androstenedione. In the crystal, inter-molecular O-H⋯O hydrogen bonds link molecules into a corrugated sheet, which lies parallel to the ab plane. Ring A has a slightly distorted half-chair conformation, rings B and C adopt chair conformations, while the cyclo-pentane ring D adopts a 14α-envelope conformation.