Synthesis of phosphoramide mustard analogues belonging to the L-sugar series

During the past decades numerous cyclophoshamide (mustard) derivatives of nucleosides and aminodeoxy sugars have been prepared for investigating their antitumor activities. The cyclophosphamide analogues of aminotrideoxy hexoses belonging to the D-series of sugars have been prepared by Monneret et al. The present paper reports the synthesis of the new phosphoramide mustards 16-17 from 12 and 15 (belonging to the L-sugar series). First compound 10 was synthesized from the L-rhamnose (9). Methyl 3-azido-2,3,6,-trideoxy-alpha-L-ribo-hexopyranoside (11) was obtained by the replacement of the 3-O-p-toluene-sulfonyl group of 10 with sodium azide. Methyl 3-azido-2,3,6,-trideoxy-alpha-L-arabino-hexopyranoside (14) was synthesized by rign opening of 13 with sodium azide. The corresponding amino sugars (12, 15) were obtained by catalytic hydrogenation (over palladium on carbon) of 11 and 14. Our compounds 12 and 15 were transformed into the cyclophosphamide derivatives 16a,b-17a,b upon treatment with bis(2-chloroethyl)phoshoramidic dichloride in the presence of triethylamine (36 h, r.t.). The approximately 1:1 mixtures of isomers (due to the different steric position of the P=O group) could be readily separated by chromatography. The 1H NMR assignments of compounds 16a, 16b, 17a and 17b, were based on one-dimensional selective decoupling experiments or two-dimensional chemical shift-correlated spectroscopy (COSY-60). The assignment of configuration to the isomeric phosphoramidates was based on the magnetic anisotropy of the P=O bond. The distinctly different chemical shift patterns of sugar protons observed for the two isomers allowed the unambiguous assignment of the P=O stereochemistry. The compounds 16a,b-17a,b (mixture of isomers) were tested for inhibitory activity using L1210 and HT29 cell lines.