The design, synthesis and anticancer activity of new nitrogen mustard derivatives of natural indole phytoalexin 1-methoxyspirobrassinol.

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 designed as prospective dual-action compounds with DNA-alkylating effect and glutathione-depleting effects that may sensitize cancer cells to alkylating agents. Both new compounds demonstrated cytostatic/cytotoxic effects on various leukemia and ovarian cancer cell lines and dsDNA-destabilizing effects in vitro. Compound 4, the more promising of the two compounds, exerts earlier onset of anticancer effects on Jurkat cells via induction of apoptosis compared to the traditional alkylating anticancer agent melphalan. In addition, it demonstrated higher potency on ovarian cancer OVCAR-3 cell line and lower fold resistance between Jurkat and Jurkat-M cells selected for the resistance to melphalan. Therefore, compound 4 may be less affected by certain cancer drug resistance mechanisms than melphalan and it may become a prototype of a new class of anticancer active nitrogen mustards that combine DNA-damaging and DNA-damage-sensitizing properties.

Cruciferous phytoalexins: antiproliferative effects in T-Jurkat leukemic cells.

We tested antiproliferative activity of selected cruciferous phytoalexins including brassinin, 1-methoxybrassinin, (+/-)-spirobrassin, (+/-)-1-methoxyspirobrassinin and (+/-)-1-methoxyspirobrassinol, in leukemic Jurkat cell. The most effective of the tested phytoalexins was 1-methoxybrassinin with IC(50) 10 micromol l(-1). However, significant effect of all phytoalexines was also determined at concentration 1 micromol l(-1). In 1-methoxybrassinin-treated Jurkat cells, we found significant increase in the fraction of cells with a sub-G(0)/G(1) DNA content, which is considered to be a marker of cell death by apoptosis. Apoptosis was also confirmed by the annexin V staining. In summary, 1-methoxybrassinin exerted potent antiproliferative activity probably due to cell cycle arrest and apoptosis induction.

Antiproliferative and cancer chemopreventive activity of phytoalexins: focus on indole phytoalexins from crucifers.

Phytoalexins are produced by plants after exposure to physical, biological or chemical stress and a specific group of these metabolites represent indole phytoalexins produced by important plants of the family Cruciferae. With respect to the epidemiologically proven cancer chemopreventive properties of brassica vegetables, antiproliferative and anticarcinogenic activities of indole phytoalexins have been studied. Several indole phytoalexins (i.e. brassinin, spirobrassinin, brassilexin, camalexin, 1-methoxyspirobrassinin, 1-methoxyspirobrassinol and methoxyspirobrassinol methyl ether) have been found to possess significant antiproliferative activity against various cancer cells and this activity is supposed to be associated with the modulation of activity of transcription factors regulating cell cycle, differentiation and apoptosis. Indole phytoalexins (i.e. cyclobrassinin, spirobrassinin, brassinin) also exhibited cancer chemopreventive activity in models of mammary and skin carcinogenesis. Understanding the molecular and cellular mechanism of action of such drugs and their structure-activity relationships is necessary for development new derivatives with more favourable profile of antiproliferative and chemopreventive activities.

Synthesis, absolute configuration, and enantiomeric enrichment of a cruciferous oxindole phytoalexin, (S)-(-)-spirobrassinin, and its oxazoline analog.

Stereochemical studies of a cruciferous oxindole phytoalexin, (S)-(-)-spirobrassinin [(-)-4], and its oxazoline analogue, spirooxazoline (11), were carried out. Racemic spirobrassinin [(+/-)-4] was synthesized by SOCl(2)- or MsCl-mediated cyclization of dioxibrassinin [(+/-)-8]. Treatment of (3-hydroxyoxindol-3-yl)methylammonium chloride [(+/-)-9] with CSCl(2) and subsequent methylation of the obtained spirooxazolidinethione (+/-)-10 afforded spirooxazoline [(+/-)-11]. Enantioresolution of (+/-)-4 and (+/-)-11 was achieved by derivatization with (S)-(-)-1-phenylethyl isocyanate (12), chromatographic separation of diastereomeric amides 13, 14 or 15, 16, and their cleavage with CH(3)ONa. Absolute configuration of the stereogenic center in natural (S)-(-)-4 was derived from the exciton, calculated via CD methods, and unequivocally confirmed by X-ray crystallographic analyses of 1-[1'S,4'R-(-)-camphanoyl] derivatives [(-)-19 and (-)-20] of (+)- and (-)-4. Novel enantiomeric enrichment phenomena of 4 and 11 were discovered during their chromatographic separations under achiral HPLC conditions. Screening of antifungal activity against the fungus Bipolaris leersiae revealed no significant dependence of this activity on absolute configuration.

Enantiomeric excess of a cruciferous phytoalexin, spirobrassinin, and its enantiomeric enrichment in an achiral HPLC system.

Enantiomeric purity of a cruciferous phytoalexin, spirobrassinin (1), was determined by chiral HPLC analysis. The enantiomeric excesses of two natural spirobrassinin fractions separated by nonchiral chromatography were considerably different. A significant enantiomeric enrichment was observed during the nonchiral chromatographic separation of an artificial enantiomeric mixture of 1.