A series of 2[prime or minute]-thionucleosides, as potential inhibitors of ribonucleotide reductases, has been synthesized. Treatment of the 3[prime or minute],5[prime or minute]-O-TPDS-2[prime or minute]-O-(trifluoromethanesulfonyl)adenosine with potassium thioacetate gave the arabino epimer of 2[prime or minute]-S-acetyl-2[prime or minute]-thioadenosine which was deacetylated to give 9-(3,5-O-TPDS-2-thio-[small beta]-d-arabinofuranosyl)adenine in high yield. Treatment of the latter with diethyl azodicarboxylate-C(3)H(7)SH-THF gave 2[prime or minute]-propyl disulfide which was desilylated to give 9-(2-deoxy-2-propyldithio-[small beta]-d-arabinofuranosyl)adenine. Subsequent tosylation (O5[prime or minute]) and displacement of the tosylate with pyrophosphate afforded the 5[prime or minute]-O-diphosphate in a stable form as propyl mixed-disulfide, which upon treatment with dithiothreitol releases 9-(2-thio-[small beta]-d-arabinofuranosyl)adenine 5[prime or minute]-diphosphate. The arabino 2[prime or minute]-mercapto group might interact with the crucial thiyl radical at cysteine 439 leading to the inhibition of ribonucleotide reductases via formation of a Cys439-2[prime or minute]-mercapto disulfide bridge. The 2,6-diamino-, 2-amino-6-chloro- and 2-amino-6-methoxypurine ribosides were also converted to the corresponding 2[prime or minute]-deoxy-2[prime or minute]-propyldithio-[small beta]-d-arabinofuranosyl nucleosides, which might serve as convenient precursors to the arabino epimer of 2[prime or minute]-thioguanosine. Analogously, 2[prime or minute]-deoxy-2[prime or minute]-propyldithioadenosine was prepared from 9-([small beta]-d-arabinofuranosyl)adenine. The nucleoside disulfides show modest cytotoxicity in a panel of human tumor cell lines.
Reaction of the diethyl 2-nitro-4-(trifluoromethyl)benzylidenemalonate with diethylamine in alcohols resulted in the reduction of the nitro group and the oxidation of the vinylic carbon attached to the phenyl ring. Simultaneous migration of the malonic fragment gave the appropriate 2-amino-4-(trifluoromethyl)benzoate esters. The presence of at least two nitro groups, or one nitro group and trifluoromethyl group on the phenyl ring, attached to the α-carbon and strongly electron withdrawing substituents at the β-carbon (CO2Et, CN) in ortho-nitrobenzylidene systems is necessary for this reductiveoxidative rearrangement to proceed. Reaction of nitrocinnamates with thiols in the presence of triethylamine in tetrahydrofuran gave Michael addition products with different regioselectivity of addition. Ethyl 2-nitrocinnamate undergoes standard β-addition of thiols to a carboncarbon double bond. However, 2,4-dinitro- and 2,4,6-trinitrocinnamates undergo α-addition of thiols, indicating that the presence of two nitro groups on the phenyl ring can reverse polarity of the carboncarbon double bond in cinnamate acceptors.Key words: abnormal Michael reactions, aromatic nitro compounds, benzylidene compounds, rearrangements.
We demonstrate that nucleophilic addition to α,β-unsaturated carbonyl compounds can be redirected from the usual β-carbon (Michael) to an α-carbon regioselectivity by attaching a π-deficient aromatic substituent to the β-carbon atom. In particular, propanethiol addition to 3-(pyridin-3-yl or pyrimidin-2-yl)propenoate gives a β-carbon adduct, while addition to the corresponding more π-deficient N-oxides gives the α-adduct or a mixture of α-and β-adducts. This adds to the number of carbon-carbon bond-forming reactions at the α-position of Michael receptors documented recently. Density
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