Abstract
Microbial hydroxylation of tedonodiol, an eremophilane alcohol, was carried out with Aspergillus niger cultures, yielding the 2α - hydroxyderivative.
Introduction
Since 1986, we have performed a project enclose in a extraction of carbonyl α,β-insaturated compounds from natural sources and chemical transformations of them, in order to provide metabolites to be tested as gastrointestinal citoprotective agents [1]. In this context we have carried out biotransformation reactions of tedonodiol, an eremophilane alcohol, isolated from Tessaria dodoneaefolia [2]. Several Aspergillus niger strains were used with this purpose.
Experimental
Culture media
Modified Czapek broth [3] was used for performed bioconversions assays, and agar Czapek was used to maintainning the strains.
Strains
Aspergillus niger ATCC 11394, Aspergillus niger Buenos Aires and a regional Aspergillus niger strain isolated from leaves of Artemisia douglassiana Besser.
Culture conditions
Biotransformations were carried out by two steps fermentation procedure [4]. Fermentations were performed in conical flasks (3 x 125 ml) with 25 ml of culture medium, on shaken at 180 r.p.pm. and incubated at 28°C. Substrate was dissolved in DMSO and added to 72 h old cultures ( final concentra-tion 1mg.ml-1). The process was continued for 7 days. Biotransformation product was recovered from the broth by liquid - liquid extraction with Et2O. Extracts were concentrated, and the solid was purified by C.C. with n-hexane - EtOAc mixtures of increasing polarity.
Results and Discussion
Only the fermentation process carried out with Aspergillus niger Buenos Aires yield a more polar product than tedonodiol in the fraction n- hexane - EtOAc (20 : 80). By the comparison of the sustrate and product 1H - NMR spectra it was possible determinated that an α - hydroxyl group incorporated on C-2 A new signal at δ 4.12 ddd (J1=J2= 2.9 Hz y J3= 3,8 Hz) corresponding to the new allylic oxy-genated methine group, confirm this fact.
Usually, microbial hydroxylation shows high regioselectivity on molecules with activated positions [5], like tedonodiol C-2 allylic position.
Acknowledgements
This work was performed with support of CONICET and U.N.S.L. (Project 7301).
References and Notes
- Rodriguez, A.M.; Enriz, R.D.; Santagata, L.; Jáuregui, E.; Pestchanker, M.; Giordano, O. Journal of Medicinal Chemistry 1997, 40, 1827. [PubMed]
- Guerreiro, E.; Kavka, J.; Giordano, O.S. Anales de Asoc. Qca. Argentina 1979, 67, 119.
- Pruna, B.R.; Bhattacharya, P.R. Applied Microbiology 1969, 10, 524.
- Carreras, C.R.; Rodriguez, J.; Silva, H. J.; Rossomando, P.; Giordano, O.S.; Guerreiro, E. Phytochemistry 1996, 41, 473.
- Carrizo, R.; Tonn, C.; Guerreiro, E. Natural Product Letters 1998, 12, 271.