Synthesis and biological activity of 26-norbrassinolide, 26-norcastasterone and 26-nor-6-deoxocastasterone

26-Norbrassinolide, identified as a metabolite of brassinolide in cultured cells of the liverwort, Marchantia polymorpha, as well as 26-norcastasteron e and 26-nor-6-deoxocastasterone were synthesized. Synthesis of these new b rassinosteroids was conducted by employing the orthoester Claisen rearrange ment and asymmetric dihydroxylation as key reactions. The modified rice lam ina inclination test indicated that these three 26-norbrassinosteroids were less active than their corresponding C-28 brassinosteroids. Growth-promoti ng activities were also examined by using the brassinosteroid-deficient, dw arf mutant lkb of garden pea (Pisum sativum L.). In this assay, 26-norbrass inolide was as effective as brassinolide and 26-norcastasterone was more ef fective than castasterone although 26-nor-6-deoxocastasterone was much less effective than 6-deoxocastasterone. Therefore, removal of C-26 of brassino steroids does not necessarily reduce the biological activity. The role of C -26 removal in Marchantia cells remains unclear. (C) 2001 Elsevier Science Ltd. All rights reserved.