Luminescence of biologically active 24-epicastasterone and a model compound

Abstract

UDC 547;535.37 Biologically active brassinosteroid 24-epicastasterone, ring B of which contains a C=O group and has the nπ * -configuration for a low-lying electronic excited state, exhibits rapid fluorescence. The wavelengths of the fluorescence maxima of the steroid dissolved in hexane and acetonitrile are equal to 332 and 394 nm, respectively. The fluorescence lifetime of the steroid dissolved in acetonitrile is τ = 9.9 nsec. Solutions of 24-epibrassinolide do not luminesce. The long-wavelength electronic absorption band λ max abs = 340 nm in the absorption spectrum of an ethanol solution of model compound 2, ring D of which contains a C=O group π * -conjugated with the C=C double bond of ring C, like in the spectrum of the steroid, has a low extinction coefficient. An ethanol solution of 2 does not fluoresce. 24-Epicastasterone at 77 K in ethanol solution exhibits phosphorescence with λ max phos = 447 nm. The phosphorescence decay is exponential with τ = 0.79 msec.Compound 2 also phosphoresces. The phosphorescence spectrum of its ethanol solution has a maximum at 490 nm. The phosphorescence decay is nonexponential in the early stage. The phosphorescence lifetime is 25 msec in the exponential decay region.

Synthesis and spectral-luminescence properties of the conjugate of 24-epibrassinolide with porphyrin

“…Molecules with nπ * -type electronic transitions usually have weak fluorescence or none at all. The luminescence properties of the biologically active representative of the brassinosteroids, 24-epicastasterone, have been studied elsewhere [9], but solutions of 24-epibrassinolide do not luminesce. Thus, the spectral and luminescence properties of the conjugate (3) will be entirely determined by the characteristics of the porphyrin marker.…”

BODIPY Conjugate of Epibrassinolide as a Novel Biologically Active Probe for In Vivo Imaging

“…For example, biological activity has been reported for the conjugates of auxin [ 21 , 22 ], ABA [ 23 , 24 , 25 ], cytokinins [ 26 ] and jasmonic acid [ 27 ]. For brassinosteroids, a number of fluorescent conjugates have been synthesized [ 25 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 ]. These conjugates have been mostly used in vitro, in the context of BRs quantitation, by HPLC [ 34 ] or in immunosorbent assays [ 34 , 37 , 38 ].…”