Brassinosteroids

Brassinosteroids (BRs) are hydroxylated derivatives of cholestane and their structure variations comprise substitutions pattern on ring A, B and the C-17 side chain (Fig. 6.10). The BRs are classified as C27, C28/ or C29 BRs, depending on the substitutions and the length of the side chain. More than 70 BRs as well as more than 42 BR metabolites have been isolated and identified (Bajguz and Tretyn, 2003). 

BRs are specific plant steroid hormones that are essential for normal plant development (Adam and Schneider, 1999 Adam et al, 1999 Bishop and Koncz, 2002 Asami et al, 2005). They act on different levels in multiple 

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6-Deoxoc4iFy i ittrcrone 6-Di hy droc stcisterone Ciisbisierone BniHHinollde 

Initially, the BR bios mthetic pathway was elucidated in Catharanthus roseus cell cultures by analysing the conversion products and intermediates (Fujioka et al, 1997). More recently, the biosynthesis of BRs has mainly been studied in Arabidopsis thaliam. Many of the genes encoding BR biosynthetic enzymes have been cloned using BR biosynthesis mutants of Arabidopsis thaliana, pea, tomato and rice. These mutants are BR deficient and revert to a wild-type phenotype following treatment with exogenous BRs. 

The key steps were the same as those used for the synthesis of dolicholide (31) and dolichosterone (34) (i) chain elongation by means of organoaluminum chemistry, (ii) stereoselective epoxidation of the resulting allylic alcohol, and (iii) regio- and stereoselective cleavage of the epoxy ring. 

Because homodolicholide (32) and homodolichosterone (35) possess the same carbon skeleton as that of stigmasterol, their alternative syntheses were achieved, utilizing all the carbon atoms of stigmasterol.77 79 

6 Synthesis of 25-methyldolichosterone, 25-methyl-2,3-diepidolichosterone, 25-methylcastasterone and 25-methylbrassinolide 

Synthesis of brassinolide and castasterone. Reprinted with permission of Shokabo Publishing 

As a result, 25-methylbrassinolide (40) was found to be more bioactive than the natural brass-inolide. Later, 25-methyl-2,3-diepidolichosterone (38) was isolated from Phaseolus vulgaris. 25-Methyldolichosterone (37) and 25-methylcastasterone (39) were also synthesized.81 

This is a relatively new group of naturally occurring steroids with remarkable biological activity (see Section XV.2). The first member isolated was brassinolide 

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NEFF, M.M., NGUYEN, S.M., MALANCHARUVIL, E.J., FUJIOKA, S., NOGUCHI, T., SETO, H., TSUBUKI, M., HONDA, T TAKATSUTO, S., YOSHIDA, S., CHORY, J., BAS1 A gene regulating brassinosteroid levels and light responsiveness in Arabidopsis, Proc. Natl. Acad. Sci. USA, 1999, 96,15316-15323. 

Brassinosteroids and Sterols (CYP72B1, CYP85A1, CYP90A1, and CYP90B1)... 

Brassinosteroids (BR) are a group of plant steroid hormones that help to regulate many aspects of plant growth and development. Several P450s have been... 

Figure 8.3 Brassinosteroid biosynthetic pathway. DWF4 and CPD catalyze the 22a- and 23a-hydroxylation reaction, respectively, in both the early and late C-6 oxidation pathways. CYP85 catalyzes the C-6 oxidation of 6-deoxytyphasterol and 6-deoxocastasterone and tentatively the C-6 oxidation of 6-deoxocathasterone and 6-deoxoteasterone (arrows not shown). DDWF1 dark-induced DIP/7-like protein 1 DWF4 DWARF4 CPD CONSTITUTIVE PHOTOMORPHOGENESIS AND DWARF.

CLOUSE, S.D., FELDMANN, K.A., Molecular genetics of brassinosteroid action. In Brassinosteroids Steroidal Plant Hormones, (A. Sakurai, T. Yokota, and S.D. Clouse, eds,), Springer Verlag, Tokyo, 1999, pp 163-190. 

SZEKERES, M., NEMETH, K KONCZ-KALMAN, Z., MATHUR, J KAUSCHMANN, A., ALTMANN, T., REDEI, G.P., NAGY, F., SCHELL, J., KONCZ, C., Brassinosteroids rescue the deficiency of CYP90, a cytochrome P450, controlling cell elongation and de-etiolation in Arabidopsis, Cell, 1996, 85, 171-182. 

CHOE, S., DILKES, B.P., FUJIOKA, S., TAKATSUTO, S., SAKURAI, A., FELDMANN, K.A., The DWF4 gene of Arabidopsis encodes a cytochrome P450 that mediates multiple 22-hydroxylation steps in brassinosteroid biosynthesis, Plant Cell, 1998,10, 231-243. 

NEFF, M. M., NGUYEN, M.S., BAS1 A gene regulating brassinosteroid levels and light responsiveness in Arabidopsis, Proc. Natl. Acad. Sci. USA, 1999, 96, 15316-15323. 

SHIMADA, Y, FUJIOKA, S., MIYAUCHI, N., KUSHERO, M., TAKATSUTO, S., MONURA, T., YOKOTA, T., KAMIYA, Y., BISHOP, G.J., YOSHIDA, S., Brassinosteroid-6-Oxidases from Arabidopsis and tomato catalyze multiple C-6 oxidations in brassinosteroid biosynthesis, Plant Physiol., 2001,126, 770-779. 

Brassinosteroids, as natural plant growth regulators, 73 22-28 Brass mills, 7 671, 690 Brass plating, 9 766, 809-810 Braunite, 75 540 Bravais lattices, 8 114t Brazeability, copper wrought alloys,... 

Campos ML, de Almeida M, Rossi ML, Martinelli AP, Litholdo Junior CG Figneira A, Rampelotti-Ferreira FT, Vendramim JD, Benedito VA, Peres EE. (2009) Brassinosteroids interact negatively with jasmonates in the formation of anti-herbivory traits in tomato. J Exp Bot 60 4347 361. 

Isoprenoids that have hormonal and signaling functions form an important group. These include steroid hormones (1 = 6) and retinoate (the anion of retinoic acid 1 = 3) in vertebrates, and juvenile hormone (1 =3) in arthropods. Some plant hormones also belong to the isoprenoids—e.g., the cytokinins, absci-sic acid, and brassinosteroids. 

Be this as it may, the CH oxidation has become an attractive and promising preparative method in natural-product synthesis. For example, dioxiranes have been used to introduce selectively a hydroxy group at the C-25 position of steroids, a challenging task not readily achieved with other oxidants. A specific case is the TFD oxidation of brassinosteroid (equation 33) . 

CS089 Ikekawa, N., S. Takatsuto, T. Kitsuwa, H. Saito, T. Morishita and H. Abe. Analysis of natural brassinosteroids by gas chromatography and gas chroma-tography-mass spectrometry. J Chroma-togrl984 290(1) 289-302. 

CSllO Abe, H., T. Morishita, M. Uchiyama, S. Takatsuto, N. Ikekawa, M. Ikeda, T. Sassa, T. Kitsuwa and S. Marumo. Occurrence of three new brassinosteroids brassinone, (24S)-24-etylbrassi-none ad 28-norbrassinolide, in higher... 

Sasa, S. Marumo and T. Kitsuwa. Microanalysis of brassinolide and its CS145 application to the identification of new brassinosteroids in plants. Proc 25th Symp on the Chem of Nat Prod Tokyo 1982 290-297. CS146... 

NT416 Park, K. H., J. D. Park, K. H. Hyun, M. Nakayama, and T. Yokota. Brassino-steroids and monoglycerides with brassinosteroid-like activity in immature seeds of Oryza sativa and Perilla frutescens and in cultured cells of Nicotiana tabacum. Biosci Biotech Biochem 1994 58(12) 2241-2243. 

Clouse, S.D. (2002) Brassinosteroid signal transduction clarifying the pathway from ligand perception to gene expression. Mol. Cell 10, 973-982. 

The kinds of compounds that elicit signals in plants are similar to certain signaling molecules in mammals (Fig. 12-28). Instead of prostaglandins, plants have jas-monate instead of steroid hormones, brassinosteroids. 

Receptorlike Protein Kinases Transduce Signals from Peptides and Brassinosteroids... 

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