Solution electronic spectra of brassinosteroid and a synthesized conjugate of a steroid and a fluorescent label

Abstract

Electronic absorption spectra of 24-epicastasterone and 24-epibrassinolide solutions have been recorded and analyzed. The long-wavelength band in solution spectra of the former steroid with maxima in the region 292-286 nm is assigned to the electronic nπ * -transition of a carbonyl chromophore. The latter steroid contains an O-C=O group, for which the extinction coefficient in this spectral region is approximately one order of magnitude less. These differences can be used to identify the studied steroids. A method to synthesize the conjugate of 24-epicastasterone with a fluorescent label, dansylhydrazine, which shows intense fluorescence and absorption, is described. Absorption spectra of the label and conjugate in diethylether, tetrahydrofuran, ethanol, and acetonitrile solutions are practically independent of the solvent properties. The exceptions are solutions of the conjugate in hexane and water. All investigated solutions of label and conjugate show intense fluorescence. As the dielectric constant of the solvent increases, the fluorescence spectra shift to long-wavelength. The fluorescence energetic and time characteristics of both the label and conjugate are similar, which enables the conjugate to be used in developing a method for immunofluorescent analysis of the brassinosteroid 24-epicastasterone.Introduction. The first plant phytohormone brassinolide was isolated from pollen of Brassica napus in 1979 [1]. Structures of more than 60 natural compounds of the brassinosteroid class have been established to date [2]. Numerous of their analogs have been synthesized and exhibit various types of plant growth and development regulation [3]. However, spectroscopic methods of investigating and analyzing this important class of compounds are underutilized. IR spectroscopy was used mainly to confirm the course of chemical reactions during the synthesis of brassinosteroids. Investigations by IR spectroscopy of 24-epi-and 24-homobrassinolides and 24-epi-and 24-homocastasterones were recently published [4]. Electronic spectra of brassinosteroids have not been published.Herein solution electronic spectra of 24-epicastasterone, 24-epibrassinolide, the fluorescent label dansylhydrazine, and a synthesized conjugate of 24-epicastasterone with dansylhydrazine are recorded and analyzed.Experimental. The method for synthesizing the conjugate 3 is exceptionally simple. The target compound 3 was obtained in one step by storing 24-epicastasterone (1) and dansylhydrazine (2) in a mixture of dimethylformamide (DMF) and acetic acid (AcOH) at room temperature:

Synthesis and spectral and luminescence properties of new conjugates of brassinosteroids for immunofluorescence analysis

“…The presence of a fluorescent group in the studied compounds enables them to be detected by instrumental methods based on luminescence measurements. Such a capability was demonstrated earlier using the conjugate of 24-epicastasterone and dansylhydrazine [3].…”

“…The fluorescence excitation spectra were consistent with the absorption spectra. The conjugate of 24-epicastasterone with dansylhydrazine that was synthesized by us earlier [3] fluoresced with a similar quantum yield of 0.4. However, its extinction coefficient of 4,600 L·mol -1 ·cm -1 was much less than that of conjugate 5.…”

“…The presence of a fluorescent group in the studied compounds enables them to be detected by instrumental methods based on luminescence measurements. Such a capability was demonstrated earlier using the conjugate of 24-epicastasterone and dansylhydrazine [3].Herein the synthesis and spectral and luminescence properties of new conjugates of brassinosteroids with various types of luminophores are reported as a continuation of research on the creation of fluorescent probes for immunochemical analysis of this class of compounds [3,4].Conjugate 5 of 24-epicastasterone 1 [5] with nitrobenzofurazan was prepared according to Scheme 1. …”

“…Herein the synthesis and spectral and luminescence properties of new conjugates of brassinosteroids with various types of luminophores are reported as a continuation of research on the creation of fluorescent probes for immunochemical analysis of this class of compounds [3,4].…”

Luminescence of biologically active 24-epicastasterone and a model compound

“…Electronic absorption spectra of solutions of 24-epicastasterone and 24-epibrassinolide have been reported [8]. A common property of the spectra of these solutions was the small extinction coefficient ε in the region 350-270 nm.…”