Stereochemistry, tautomerism, and reactions of acridinyl thiosemicarbazides in the synthesis of 1,3‐thiazolidines

Abstract

Acridin‐9‐yl hydrazine upon treatment with various isothiocyanates (RNCS, R = methyl, allyl, phenyl, p‐methoxy phenyl, and p‐nitro phenyl) yielded the corresponding thiosemicarbazides with acridine substituted on the carbazide‐type side. The alkyl‐substituted compounds were present in solution as equilibria consisting of the major H‐10, H‐12 tautomer (either E or Z or both about the C13‐N14 bond) and the minor H‐10, SH tautomer (either E or Z or both). The major species for the aromatic‐substituted compounds was the H‐10, H‐12 E tautomer, with the evident minor species being the H‐10, H‐12 Z tautomer. The thiosemicarbazides were each quantitatively converted into the analogous semicarbazides upon treatment with mesitylnitrile oxide wherein all structures were present in solution as the H‐10 tautomers with Z conformation about the C13‐N14 bond. Methylation of the compounds with methyl iodide yielded S‐methylated compounds wherein the Z configuration dominated in each case over the E configuration along the N12‐C13 double bond. Treatment of the thiosemicarbazides with methyl bromoacetate resulted in the formation of 1′,3′‐thiazolidin‐4′‐ones wherein the Z configuration predominated in each case over the E configuration along the N12C13 double bond. With bromoacetonitrile as the bifunctional electrophile, the initial 1′,3′‐thiazolidin‐4′‐imines that formed spontaneously underwent Dimroth‐type rearrangement to the regiosiomeric 1′,3′‐thiazolidin‐4′‐imines.

Characterization and Quantitation of Polyphenolic Compounds in Senna splendida from the Northeast of Brazil

“…The chemical shifts of 13 C nuclei are reported to two decimal places when sharp signals were observable directly or one decimal place when the peak was broad or the signal was observed indirectly. General NMR experimental and acquisition details for 1D 1 H, 13 C, DEPT, and 1D-selective NOESY observation and standard gradient-selected 2D COSY, HSQC, and HMBC spectra and routine chemical shift assignment using 2D NMR have been previously described [14][15][16][17]. Signal assignments were also assisted by iterative calculation of chemical shifts using the chemical shift prediction routine within the ChemDraw 12.0 (www.cambridgesoft.com) program when inconclusive by correlation spectra.…”

Formation of 5-Hydroxy-3-methoxy-1,4-naphthoquinone and 8-Hydroxy-4-methoxy-1,2-naphthoquinone from Juglone

“…The chemical shifts of 1 H and 13 C nuclei are reported relative to TMS incorporated as an internal standard ( δ = 0 ppm for both 1 H and 13 C). General NMR experimental details for 1D 1 H, 13 C, and DEPT and standard gradient-selected 2D DQF-COSY, HSQC, and HMBC spectra have been previously described [17–20] for routine structural determinations and chemical shift assignments. For 1D selective COSY (set on a J value of 7 Hz for vicinal coupling whilst for long-range J , values varied in the range 0.25–1 Hz) and NOESY [21, 22] (mixing times: 0.5, 0.75 s) experiments, selective excitation was effected using a 180° 50 ms Gaussian-shaped pulse via excitation sculpting [23].…”

Anticancer potential of rhizome extract and a labdane diterpenoid from Curcuma mutabilis plant endemic to Western Ghats of India

“…The chemical shifts of 1 H nuclei are reported to three decimal places when the multiplet was amenable to first-order analysis or to two decimal places when the multiplet was beyond such interpretation; for overlapped signals, chemical shifts were taken from 2D NMR spectra and are reported to three decimal places to distinguish them. General NMR experimental and acquisition details for 1D 1 H, 13 C, and DEPT observation and standard gradient-selected 2D COSY, HSQC, HMBC,and NOESY spectra and routine chemical shift assignment using 2D NMR have been previously described [52][53][54] .…”