Ring Transformations of Semicyclic 1,3-Dicarbonyl Heteroanalogs; IV¹. Synthesis of 3-(ω-Aminoalkyl)-1,2,4-thiadiazoles by Ring Transformation Reaction of Semicyclic Thioacylamidines with 3,3-Pentamethyleneoxaziridine

Chemical Investigation of the Indonesian Tunicate Polycarpa aurata and Evaluation of the Effects Against Schistosoma mansoni of the Novel Alkaloids Polyaurines A and B

“…Thus, we hypothesized the third structural subunit in the molecule of compound 2 to be a 1,2,4-thiadiazole ring (subunit C, Figure 3), the only thiadiazole regioisomer known to occur naturally [1] and already found in the structure of polycarpathiamines previously discovered from P. aurata [5]. Comparison of the chemical shift values of compound 2 , and precisely evaluation at δ c values of the two carbons assigned to the heterocyclic ring, with those reported in the literature for both natural [5,12,13,14] and synthetic 1,2,4-thiadiazole alkaloids [14,15,16,17] allowed to substantiate this assumption.…”

“…To unequivocally prove the existence of the unusual 1,2,4-thiadiazole heterocyclic ring, structure elucidation of these compounds has been confirmed by synthesis [14,15,16,17] with respect of many spectroscopic evidences as well as biogenetic considerations. Instead, we obtained further support to the methyl 5-(4-methoxyphenyl)-1,2,4-thiadiazol-3-yl)(methyl)carbamate structure proposed for polyaurine B, through the quantum mechanical calculation of its 13 C NMR chemical shifts profile and application of DP4+ statistical analysis.…”