Side Chain Conformation of the Growth-Promoting Phytohormones Brassinolide and 24-Epibrassinolide

Abstract

Quantitative 2D NOE measurements and restrained molecular dynamics simulations (with explicit solvent) were carried out in order to determine preferential solution side chain conformations of the two most important native brassinosteroids, brassinolide and 24‐epibrassinolide. The NOE assignment was assisted by 1D NOE difference spectroscopy and included prochiral assignment of the side chain methyl groups Me‐26 and Me‐27. 2D NOE intensities were converted into inter‐proton distances using the ‘complete relaxation matrix analysis’ methodology. Restrained molecular dynamics simulations in a chloroform solvent box led to a well defined solution conformation in the case of brassinolide. The increased side chain flexibility in the case of 24‐epibrassinolide is discussed, considering missing NOE correlations and vicinal proton coupling constants. © 1997 by John Wiley & Sons, Ltd.

Ulososides and Urabosides — Triterpenoid Saponins from the Caribbean Marine Sponge Ectyoplasia ferox

“…The relative configuration of the tetracycle was confirmed by NOESY correlations and 3 J scalar coupling interpretation [23]. We decided to assess the relative configuration of the asymmetric centers at C-22, C-23 and C-24 of the side-chain using a close inspection of the NMR data reported for the closely related and well known brassinosteroids [23,24,25].…”

Brassinosteroid phytohormones: structure, bioactivity and applications

“…In regard to the more flexible side-chain conformation, a series of 10 brassinosteroids were investigated by means of detailed NMR investigations, molecular modeling studies, and compared with data from X-ray analysis. For the most bioactive compound brassinolide (1) the majority of conformations in solution showed a side-chain bent towards the β-face of the steroid skeleton, whereas for the less active members like 24-epibrassinolide conformations with straight side-chains or side-chains bent towards α-face are preferred (see partial structures 203 and 204 in figure 28; Stoldt et al, 1997;Drohsin et al, 2001). While these models are valuable approaches for the design of new brassinosteroid analogues, it must be remembered that they may not furnish the actual active conformation of a brassinosteroid inside the receptor site of an enzyme.…”

NMR and X-ray studies of isomeric 22,23-dihydroxy stigmastanes

“…The preferred conformations of BS side chain were subject of numerous studies, especially those involving molecular modeling approaches [5][6][7][8][9][10][11]. The obtained conclusions can be based on some speculations and should be verified experimentally.…”

“…The chemical structures of homocastasterone (1), (22S,23S)-homocastasterone (2) and model compounds(3)(4)(5)(6).…”