Brassinosteroids. A New Class of Plant Hormones by V. A. Khripach, V. N. Zhabinskii, A. E. de Groot

By V. A. Khripach, V. N. Zhabinskii, A. E. de Groot

Within the monograph, the result of clinical investigations carried out by means of researchers of the Institute of Bioorganic Chemistry of tne nationwide Academy of Sciences of Belarus (Minsk, Belarus) and the dept of natural Chemistry of the Wageningen Agricultural college (Wageningen, The Netherlands) are provided. The ebook covers constructions, class, isolation, spectroscopic decision, biosynthesis, metabolism, physiological mode of motion, useful purposes in agriculture, and so forth. of a brand new type of plant hormones - brassinosteroids.

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Extra info for Brassinosteroids. A New Class of Plant Hormones

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J,,i, iU,ii K -Ml Fig. 17. Mass spectrum of epibrassinolide bismethaneboronate (EI, 70 eV). A substituent at C-24 (alkyl or alkenyl) greatly influences the character of the fragmentation. For saturated BS the most characteristic are peaks resulting from cleavage of the C-23 - C-24, C-20 - C-22, and C-17 - C-20 bonds (Ikekawa et ai, 1984; Takatsuto, 1994a). Thefragmentions for tetrahydroxy lactones at m/z 457 and for tetrahydroxy ketone derivatives at m/z 441 are the result of C-23 C-24-fission (Scheme 4).

Along with ions corresponding to cleavage of carbon - carbon of bond [M-X]^, appropriate ions caused by one-, two-, and three-step dehydrations [M-X-nH20]^ are formed. Usually in mass spectra of steroids there are also [M-X-CHs]^ peaks, formed as result of the loss of one of the angular methyl groups. An example of an EI mass spectrum of a BS is shown in Fig. 16. The spectrum of epibrassinolide shows a hardly distinguishable molecular ion peak and also the appropriate dehydration peaks. The peaks appropriate to cleavage of the C-24 - C-25 bond are also of a low intensity.

1983). The difference in chemical shifts of the 26- and 27-methyl groups demonstrates the rigidity of the steroidal side chain - even the rotation around the C-24 - C-25 bond is restricted. The signal of the 29-Me can be * NMR spectra in CDCI3 are discussed, if not indicated otherwise. 5 Hz. 1 Hz. 0, with the signals of most of the methine and methylene protons, is excessively overcrowded. ^H-^H COSY 2D NMR offers a method for a detailed analysis of this region (Porzel et aL, 1992; Ando et al, 1993; Adam et al, 1996b).

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