Addition of deoxyribose to guanine and modified DNA bases by Lactobacillus helveticus trans-N-deoxyribosylase

The use of bacterial trans-N-deoxyribosylase was evaluated as an alternative method for deoxyribosylation in the synthesis of deoxyribonucleosides containing potentially mutagenic adducts. A crude enzyme preparation was isolated from Lactobacillus helveticus and compared to Escherichia coli purine nucleoside phosphorylase. trans-N-deoxyribosylase was more regioselective than purine nucleoside phosphorylase in the deoxyribosylation of Cua at the N9 atom, as compared to N7, as demonstrated by NMR analysis of the product, 5,6,7,9-Tetrahydro-7-acetoxy-9 -oxoimidazo[1,2-a]purine was efficiently deoxyribosylated by trans-N-deoxyribosylase but not at all by purine nucleoside phosphorylase. Other substrates for trans-N-deoxyribosylase were N-2-(2-oxoethyl)Gua, pyrimido[1,2-a]purin-10(3H)-one, 1,N-2-epsilon-Gua, N-2,-epsilon-Gua, epsilon-Gua, 3,N-4-epsilon-Cyt, 1, N-6-epsilon-Ade, C-8-methylGua, and C-8-aminoGua, most of which gave the desired isomer (bond at the nitrogen corresponding to N9 in Gua) in good yield. Neither N-7-alkylpurines nor C-8-(arylamino)-substituted guanines were substrates. The approach offers a relatively convenient method of enzymatic preparation of many carcinogen-DNA adducts at the nucleoside level, for either use as standards or incorporation into oligonucleotides. trans-N-deoxyribosylase can also be used to remove deoxyribose from modified deoxyribonucleosides in the presence of excess Cyt.