Nmr spectroscopic studies on the tautomerism in tenuazonic acid analogs

Abstract

Nmr spectra of structural analogs of tenuazonic acid such as 3‐acetyltetramic acid, 3‐acetyltetronic acid, 3‐acetylthiotetronic acid and others were investigated for elucidation of the tautomeric structures. These compounds have completely enolized β,β′‐triketone systems, and the position of the nmr signals for the enolic proton shows that the strength of their intramolecular hydrogen‐bonding is weaker than those of acyclic β,β′‐triketones and six‐membered cyclic triketones. The assignment was made for nmr signals split by the difference of the diamagnetic anisotropic effect in each tautomers. The percentages of each of the tautomers were calculated from the intensities of the corresponding nmr signals. The results were confirmed by means of 13C‐nmr spectroscopy.

Enzyme-Dependent [4 + 2] Cycloaddition Depends on Lid-like Interaction of the N-Terminal Sequence with the Catalytic Core in PyrI4

“…Consequently, a synergistic conformation constraint in the rigid b barrel structure of PyrI4 plays a crucial role in the conversion of 1 to 2, as multiple mutations of these residues, Q115A/Y85A, Q115A/ Y85A/E65A, Q115A/Y85A/E65A/E87A, Y85A/E65A/E87A, and Y85A/E65A/E87A/Y177A, showed additive effects toward the nearly complete inactivation of the enzyme ( Figure 4C). The acidic pocket of the b barrel provides an internal environment that may facilitate negative charge removal from the tetramate moiety of 1 (Yamaguchi et al, 1976) to lower the LUMO energy of dienophile, thereby allowing the Diels-Alder-like cyclization to proceed under the condition of physiological pH.…”

Synthesis and antibacterial activity of monocyclic 3-carboxamide tetramic acids

“…Tautomerism in tricarbonyl 3-acyltetramate systems is known to be complex and strongly dependent on the identity of the side chain acyl group [23]. 3-Acyl (X = CH 2 ) [10,24–25], 3-carboxamide (X = NH) [8,10] and 3-alkoxycarbonyl (X = O) tetramic acids (Fig.…”

“…The tautomerisation of 3-acyltetramic acids has been shown to be mainly affected by substitution on N(1) rather than the functionalities on the 3-acyl and C(5) positions. Thus, the dominant tautomer of N-unsubstituted and N -alkyltetramates is D, while N -acyltetramates exist as a mixture of external tautomers AB and D in approximately equal ratio [23]. By contrast, it was found that the tautomerisation of 3-carboxamides and 3-alkoxycarbonyls was not affected by substitution on N(1).…”

Syntheses and biological activities of tetramic acid and tetronic acid derivatives.

“…The results of As seen in Table Ma, the pupation was inhibited by some derivatives of 5-aryltetronic acid (13,15) and the benzylidene compound (21). The mortal effect was not observed in general, but compounds (4) and (8) showed it somewhat.…”