Synthesis of new 1,2,4-triazolines and 1,3,4-thiadiazolines from bithioureas

Synthesis of Novel 1,3-thiazole-, 1,2,4-triazole- thione and Triazepine Derivatives

Reaction of the cyanoacetic hydrazide derivatives 1a–e with isothiocyanates gave the hydrazinocarboxamide and thioamide derivatives 2a–g and 1,2,4-triazole-3-thiones 3. Upon reacting 1b–d with ethyl bromoacetate followed by isothiocyanates; the 1,3-thiazole-5-carbohydrazides 5 were afforded. Cyclisation of products 1b–e with triethylorthoformate furnished the unexpected ethyl cyanoacetylhydrazonoformate 6; rather than the expected triazolethiones of type 7. A mechanism for the formation of product 6 was suggested and discussed. Upon heating product 6 with some arylamines in acetonitrile, the 5-aminotriazepin-7-ones 9 were afforded.

Formation of 5-alkylidenepyrazol-4(1H)-ones and 3-amino-6-aryl-5-cyano-pyridazine-4-carboxylates from arenealdehyde thiosemicarbazones and unsaturated 1,2-diesters

The reaction of arenealdehyde 4-phenylthiosemicarbazones 1a–f with dimethyl ethynedicarboxylate (6) gave methyl [3-aryl-4-oxo-1-(phenylthiocarbamoyl)-4,5-dihydro-1H-pyrazol-5-ylidene]ethanoates 10a–f in 73-79% yield, while, by reaction with diethyl (E)-2,3-dicyanobutenedioate (7), compounds 1a–f are transformed into ethyl [3-aryl-4-oxo-1-(phenylthiocarbamoyl)-4,5-dihydro-1H-pyrazol-5-ylidene]cyanoacetates 15a–f (54-61%) and ethyl 3-amino-6-aryl-5-cyanopyridazine-4-carboxylates 24a–f (22-26%). Rationales for these transformations are presented.

Solid-phase synthesis of positively charged deoxynucleic guanidine (DNG) modified oligonucleotides containing neutral urea linkages: effect of charge deletions on binding and fidelity

A solid-phase synthesis for a DNA analogue with a mixed guanidinium and urea backbone is reported. This material is nearly identical in structure to deoxynucleic guanidine (DNG) but the neutral urea internucleoside linkages can be used to attenuate the overall positive charge on the oligomer. The opposite charge attraction between urea containing DNG oligomers (DNGUs) and complimentary DNA can be controlled so that the affinity of DNG for DNA does not overwhelm the base-pairing discrimination necessary for specific binding. Octameric DNGU containing between 1 and 3 urea substitutions covered the range between very tight and very weak bonding. Each deletion of a positive charge reduced the thermal denaturation temperature (Tm) by approximately 5 degrees C. Mismatches in the DNA oligomers reduced the Tm values by 3 to 5 degrees C for each of the DNGU oligomers. DNGUs were found to bind in a 2:1 fashion to complimentary DNA in the same manner as DNG.