Brassinosteroids: A new way to define the structural requirements

Brosa, Carme; Capdevila, Joan; Zamora, Ismael

doi:10.1016/0040-4020(95)01065-3

Cited by 73 publications

(41 citation statements)

References 8 publications

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“…So far only brassinosteroids having such a spatial orientation of the OH groups at C 22 and C 23, which is illustrated in the structural formulas (R configuration), have been observed in plants, while compounds with the opposite S configuration of the OH groups can be obtained only synthetically. Substituents at C 24 of natural brassinosteroids can have both the R configuration (compounds 1, 2) and the S configuration (3,4).…”

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“…A condition for high biological activity of brassinosteroids is the presence in the B ring of a 6-keto (castasterone and related compounds) or 7-oxa-6-keto (brassinolide and other lactones) structural moiety, and also a 2α,3α-diol group on the A ring and a trans fusion for the A/B rings (see structural formulas). Along with these structural features, the biological activity of brassinosteroids is determined by the structure of the side chain: the presence and configurations of hydroxyl groups at the carbon atoms C 22 and C 23, and also the nature of the substituent at the carbon atom C 24 [2][3][4]. It has been established that the greatest biological activity in many test systems is shown by brassinolide, first obtained from pollen of the plant Brassica napus [5].…”

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Manifestation of structure and intermolecular interactions of biologically active brassinosteroids in infrared spectra

et al. 2007

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UDC 547;535.34;543.42.We have analyzed the IR spectra obtained for steroidal phytohormones 24-epibrassinolide, 24-epicastasterone, 28-homobrassinolide, and 28-homocastasterone. The characteristic frequencies of the stretching vibrations of the hydrocarbon groups CH 3 , CH 2 , and CH and also the C=O groups in the spectra of brassinolides are higher than in the spectra of castasterones, which makes it possible to identify them from the IR spectra. Study of the spectra of these brassinosteroids in different media (pressed samples in KBr, films, solutions in CHCl 3 and CDCl 3 ) allowed us to establish the presence of intermolecular interactions in which C=O and OH groups, OH-OH groups participate, and also the possible formation of intramolecular hydrogen bonds between the OH groups of the molecules.Introduction. Brassinosteroids are a new class of natural and synthetic steroidal phytohormones [1] which play a key role in regulation of the growth and development of plants, and also have good prospects for use in medicine and veterinary practice as new pharmacological agents. A condition for high biological activity of brassinosteroids is the presence in the B ring of a 6-keto (castasterone and related compounds) or 7-oxa-6-keto (brassinolide and other lactones) structural moiety, and also a 2α,3α-diol group on the A ring and a trans fusion for the A/B rings (see structural formulas). Along with these structural features, the biological activity of brassinosteroids is determined by the structure of the side chain: the presence and configurations of hydroxyl groups at the carbon atoms C 22 and C 23, and also the nature of the substituent at the carbon atom C 24 [2][3][4]. It has been established that the greatest biological activity in many test systems is shown by brassinolide, first obtained from pollen of the plant Brassica napus [5]. However, a clear interconnection between the structure and the biological properties of brassinosteroids has not yet been established. This makes large-scale use of brassinosteroids in agriculture as plant growth stimulators difficult, and limits their advance into other areas of application.Despite the fact that the IR spectra provide considerable information about the structure and interactions of molecules, in study of brassinosteroids, IR spectroscopy methods have been used mainly to confirm the course of chemical reactions in synthesis of new compounds in this class.In this work, we used IR spectroscopy methods to study the structure and intermolecular interactions of 24-epibrassinolide (1), 24-epicastasterone (2), 28-homobrassinolide (3), and 28-homocastasterone (4), the structural formulas of which have the form:

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Manifestation of structure and intermolecular interactions of biologically active brassinosteroids in infrared spectra

et al. 2007

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“…For signals from the C 2 , C 3 , C 4 , C 5 , C 9 , and C 19 atoms, we observe the opposite shift, which for C 5 achieve the maximum value of 3 ppm. At the same time, for the isomer pair IV and V with a free diol functional group, the ratio of the chemical shifts for signals from the C 1 and C 4 carbon atoms has the opposite sign, and corresponds to that for pairs of natural brassinosteroids having a 2α,3α-cis-diol group and their 2β,3β isomers [11,15]. Obviously the different tendencies with respect to the change in the position of the C 1 and C 4 signals for pairs of 2α,3α and 2β,3β isomers for free diols and their isopropylidene derivatives are a consequence of the effect of the additional charge formed by the acetonide protective group.…”

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NMR spectra of androstane analogs of brassinosteroids

et al. 2007

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We have used two-dimensional NMR spectroscopy to make a complete assignment of signals from the nuclei of hydrogen and carbon atoms in the spectra of brassinosteroids in the androstane series. We have confirmed the stereochemistry of the chiral centers and the structure of the molecules. We have studied the effect of the configuration of the 2,3-diol groups in the A ring of the steroids on the chemical shift of adjacent atoms in the 13 C and 1 H NMR spectra.

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“…Natural and synthetic brassinosteroid (BS) phytohormones [1] possess several properties that enable them to be used in biology, medicine, and veterinary medicine as new pharmacological agents. According to the literature [2][3][4], the biological activity of BS in plants is due to the presence in their ring B of a 6-keto-or 7-oxa-6-keto structural fragment; in ring A, of a 2α,3α-diol group; and trans-fusion of rings A/B. The structure of the side chain also plays an important role, especially the presence and configuration of OH groups on C22 and C23 and the nature of the substituents on C24.…”

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IR spectra of stigmastane series brassinosteroids differing in configuration and number of diol groups

et al. 2009

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28-homosecasterol have been analyzed. The 28-homocastasterone molecule contains diol groups in ring A and in the side chain whereas that of 28-homosecasterol has one diol group in the side chain. The lack of two OH groups in ring A of homosecasterol compared to homocastasterone results in the appearance of stretching vibrational bands of H-C= (ν max = 3025 cm -1 ) and -C=C (ν max = 1656 cm -1 ) groups of ring A. Substantial changes are observed in the area of OH stretching vibrations. Homocastasterones pressed in KBr possess twice as many OH groups as homosecasterols such that absorption band total intensities in IR spectra of both isomers caused by H-bonds of the diol groups in the side chain amount to 65% whereas the share of the 2α,3α group is only 35% of the total intensity. Hence the contribution from the side-chain OH groups of the studied brassinosteroids to the integral optical density of the bands exceeds that from the ring-A OH groups. In dilute CHCl 3 solutions of the brassinosteroids, the conformations of the brassinosteroid side chains are not the same. As a result, intramolecular H-bonds of different energy are created. The optical density D max in band maxima of free OH groups for homocastasterones is three times higher than that for the corresponding band maxima of homosecasterol. This implies that D max for bands of free OH groups of the homocastasterone ring-A diol group is greater, in contrast with the relatively greater D max for bands of homosecasterol side-chain OH groups bound by an intermolecular H-bond. The homocastasterone diol groups also form intramolecular Hbonds more actively. The lack of the diol group in ring A of the homosecasterols does not affect the frequencies of the C=O stretching vibrations. This leads to the conclusion that the C=O group forms intermolecular H-bonds only with the side-chain OH groups of brassinosteroids pressed in KBr.Keywords: IR spectra, 28-homocastasterone, 28-homosecasterol, R-and S-isomers, H-bond. Introduction. Natural and synthetic brassinosteroid (BS) phytohormones [1] possess several properties that enable them to be used in biology, medicine, and veterinary medicine as new pharmacological agents. According to the literature [2][3][4], the biological activity of BS in plants is due to the presence in their ring B of a 6-keto-or 7-oxa-6-keto structural fragment; in ring A, of a 2α,3α-diol group; and trans-fusion of rings A/B. The structure of the side chain also plays an important role, especially the presence and configuration of OH groups on C22 and C23 and the nature of the substituents on C24. (22R,23R)-BS are biologically most active in the majority of tests. The corresponding (22S,23S)-isomers are not observed in nature and are prepared synthetically [1]. Slight changes in the BS structure lead to significantly different activities. However, a reliable correlation between the BS structural features and their biological properties has not been established. Therefore, investigations including the use of IR spectroscopy are interesting both pr...

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Brassinosteroids: A new way to define the structural requirements

Cited by 73 publications

References 8 publications

Manifestation of structure and intermolecular interactions of biologically active brassinosteroids in infrared spectra

Manifestation of structure and intermolecular interactions of biologically active brassinosteroids in infrared spectra

NMR spectra of androstane analogs of brassinosteroids

IR spectra of stigmastane series brassinosteroids differing in configuration and number of diol groups

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