Nitrogen mustards cis-1-methoxy-2-deoxy-2-[N,N-bis(2 -chloroethyl)amino]spirobrassinol (4) and trans-1-methoxy-2-deoxy-2-[N,N-bis(2 -chloroethyl)amino]spirobrassinol (5) derived from 1-methoxyspirobrassinol, an indole phytoalexin produced by the Japanese radish Raphanus sativus var. hortensis were