Potential bile acid metabolites. 20. A new synthetic route to stereoisomeric 3,6-dihydroxy- and 6-hydroxy-5 alpha-cholanoic acids

Synthesis of Five Known Brassinosteroid Analogs from Hyodeoxycholic Acid and Their Activities as Plant-Growth Regulators

Brassinosteroids (BRs) are plant hormones that promote growth in different plant organs and tissues. The structural requirements that these compounds should possess to exhibit this biological activity have been studied. In this work, a series of known BR analogs 5–15, were synthesized starting from hyodeoxycholic acid 4, and maintaining the alkyl side chain as cholic acid or its methyl ester. The growth-promoting effects of brassinolide (1) and synthesized analogs were evaluated by using the rice lamina inclination assay at concentrations ranging from 1 × 10⁻⁸–1 × 10⁻⁶ M. Our results indicate that in this concentration range the induced bending angle of rice seedlings increases with increasing concentration of BRs. Analysis of the activities, determined at the lowest tested concentration, in terms of BR structures shows that the 2α,3α-dihydroxy-7-oxa-6-ketone moiety existing in brassinolide is required for the plant growing activity of these compounds, as it has been proposed by some structure-activity relationship studies. The effect of compound 8 on cell elongation was assessed by microscopy analysis, and the results indicate that the growth-promoting effect of analog 8 is mainly due to cell elongation of the adaxial sides, instead of an increase on cell number.

Structural Modifications of Deoxycholic Acid to Obtain Three Known Brassinosteroid Analogues and Full NMR Spectroscopic Characterization

An improved synthesis route for obtaining known brassinosteroid analogues, i.e., methyl 2α,3α-dihydroxy-6-oxo-5α-cholan-24-oate (11), methyl 3α-hydroxy-6-oxo-7-oxa-5α-cholan-24-oate (15) and methyl 3α-hydroxy-6-oxa-7-oxo-5α-cholan-24-oate (16), from hyodeoxycholic acid (4) maintaining the native side chain is described. In the alternative procedure, the di-oxidized product 6, obtained in the oxidation of methyl hyodeoxycholate 5, was converted almost quantitatively into the target monoketone 7 by stereoselective reduction with NaBH₄, increasing the overall yield of this synthetic route to 96.8%. The complete ¹H- and ¹³C-NMR assignments for all compounds synthesized in this work have been made by 1D and 2D heteronuclear correlation gs-HSQC and gs-HMBC techniques. Thus, it was possible to update the spectroscopic information of ¹H-NMR and to accomplish a complete assignment of all ¹³C-NMR signals for analogues 5–16, which were previously reported only in partial form.

ARISTO: ontological classification of small molecules by electron ionization-mass spectrometry

Gas chromatography–mass spectrometry (GC–MS) acquisitions routinely yield hundreds to thousands of Electron Ionization (EI) mass spectra. The chemical identification of these spectra typically involves a search protocol that seeks an exact match to a reference spectrum. Reference spectra are found in comprehensive libraries of small molecule EI spectra curated by commercial and public entities. We developed ARISTO (Automatic Reduction of Ion Spectra To Ontology), a webtool, which provides information regarding the general chemical nature of the compound underlying an input EI mass spectrum. Importantly, ARISTO can provide such annotation without necessitating an exact match to a specific compound. ARISTO provides assignments to a subset of the ChEBI (Chemical Entities of Biological Interest) dictionary, an ontology, which aims to cover biologically relevant small molecules. Our system takes as input a mass spectrum represented as a series of mass and intensity pairs; the system returns a graphical representation of the supported ontology as well as a detailed table of suggested annotations along with their associated statistical evidence. ARISTO is accessible at this URL: http://www.ionspectra.org/aristo. The system is free, open to all and does not require registration of any sort.

Chemical and metabolic transformations of selected bile acids

This article surveys chemical transformations of selected bile acids. Chemical transformations were initially carried out with the aim of determining the structure of bile acids. More recently they have been concerned with bile acid interconversions as well as with the synthesis of steroid hormones, vitamins and therapeutc agents. Studies of similarities and differences in the biosynthesis of bile acids from cholesterol have occupied many researches. However, this article reviews only papers dealing with the synthesis of potential intermediates in the biosynthesis of bile acids. Steroid hormones such as pregnenolone, progesterone and testosterone are synthesized from methyl thiodeoxycholate whereas cortisone is synthesized from methyl deoxycholiate. Numerous papers and patents devoted to the synthesis of ursodeoxycholic acid from cholic or chenodeoxycholic acid testify to its effectiveness in the treatment of cholelithiasis. Chenodeoxycholic acid appears to be an excellent precursor in the synthesis of steroid plant growth regulators, as well as in the synthesis of metabolites and vitamin D analogues. Chirality of bile acids has been exploited in the synthesis of cyclic and acyclic receptors and solvents. Cholic and deoxycholic acids have been used to create new macrocyclic structures which show different capacities to bind and transport other compounds. Another important trend in the chemistry of bile acids is their application in combinatorial chemistry.