The effect of the reaction temperature and the solvent on the diastereoselectivity of the spirocyclization of 1-methoxybrassinin leading to 1-methoxyspirobrassinol methyl ether was studied. 1-Acyl derivatives of 1-methoxyspirobrassinol and 1-methoxyspirobrassinol methyl ether were prepared by the bromine-mediated spirocyclization reactions of derivatives of brassinin bearing an acyl group on the indole nitrogen with water or methanol as nucleophilic agents. The cyclization of 1-acyl derivatives of brassinin afforded the trans-diastereoisomer as the major product, whereas using 1-methoxybrassinin afforded the cis-and trans-isomers in a ratio near to 1:1. Bromospirocyclization of brassinin and 1-methylbrassinin in the presence of methanol resulted in the formation of spirobrassinin and 1-methylspirobrassinin. The newly synthesized analogues of indole phytoalexins exhibited more significant antiproliferative activity against human leukemia cell lines than the natural phytoalexins.