Analogs of the cyclic hydroxamic acid 2,4-dihydroxy-7-methoxy-2H-1,4-benzoxazin-3-one (DIMBOA): decomposition to benzoxazolinones and reaction with .beta.-mercaptoethanol
摘要:
Analogues of the aglucones of naturally occurring cyclic hydroxamic acids (2,4-dihydroxy-1,4-benzoxazin-3-ones) from Gramineae (Poaceae) have been synthesized by the reductive cyclization of the ring-substituted methyl alpha-(o-nitrophenoxy)-alpha-methoxyacetates, followed by demethylation of the C-2 methoxy group with BBr3 or BCl3 to reveal the 2-hydroxy group. A structure-activity series was produced by varying the substituent at C-7 on the aromatic ring [R = MeO (1), t-Bu (6), Me (7), H (8), Cl (9), F (10), CO2Me (11a)]. The pK(a) values for the hydroxamic acid and the phenol moieties were determined for each member of the C-7 series. They correlated well with sigma in a linear free energy relationship (LFER) yielding values of rho = 0.71 (with sigma-p) for pK(a1) (the hydroxamic acid) and rho = 1.6 (with sigma-m) for pK(a2) (the phenol). A LFER also existed between the rate constants for the unimolecular decomposition of these hydroxamic acids to benzoxazolinones and sigma+ (rho = 1.1). The rates of hydroxamic acid reduction to lactams by beta-mercaptoethanol were also investigated. It was found that only compounds with electron-rich aromatic rings and specifically an oxa functionality para to the hydroxamic acid nitrogen atom (compounds 1 and 3-5) had measurable rates of reduction. H-1 NMR spectra recorded during this reaction in D2O buffers (pD9), however, showed that compounds 1, 2, 6-9 (the only ones investigated) formed a hemithioacetal at C-2 even though only 1 has a measurable rate of reduction by the same thiol. The remarkable rate enhancement provided by an oxa functionality suggests that reduction occurs by direct attack of thiolate on the hydroxamic nitrogen of a resonance-stabilized ion pair.
环状异羟肟酸,例如2,4-二羟基-7-甲氧基-2 H -1,4-苯并恶嗪-3(4 H)-1(DIMBOA)和2,4-二羟基-2 H -1,4-苯并恶嗪-3 (4 H)-1(DIBOA)被发现在几种植物中,在植物防御各种敌人的防御系统中起着重要作用。为了研究新的机理和作用,我们使用已知的合成途径合成了分子。由于DIMBOA的化学数据不完整甚至是虚假的,我们决定在此期刊上发表缺失的数据。
ATKINSON, JEFFREY;MORAND, PETER;ARNASON, JOHN T.;NIEMEYER, HERMANN M.;BRA+, J. ORG. CHEM., 56,(1991) N, C. 1788-1800
作者:ATKINSON, JEFFREY、MORAND, PETER、ARNASON, JOHN T.、NIEMEYER, HERMANN M.、BRA+
DOI:——
日期:——
Analogs of the cyclic hydroxamic acid 2,4-dihydroxy-7-methoxy-2H-1,4-benzoxazin-3-one (DIMBOA): decomposition to benzoxazolinones and reaction with .beta.-mercaptoethanol
作者:Jeffrey Atkinson、Peter Morand、John T. Arnason、Hermann M. Niemeyer、Hector R. Bravo
DOI:10.1021/jo00005a025
日期:1991.3
Analogues of the aglucones of naturally occurring cyclic hydroxamic acids (2,4-dihydroxy-1,4-benzoxazin-3-ones) from Gramineae (Poaceae) have been synthesized by the reductive cyclization of the ring-substituted methyl alpha-(o-nitrophenoxy)-alpha-methoxyacetates, followed by demethylation of the C-2 methoxy group with BBr3 or BCl3 to reveal the 2-hydroxy group. A structure-activity series was produced by varying the substituent at C-7 on the aromatic ring [R = MeO (1), t-Bu (6), Me (7), H (8), Cl (9), F (10), CO2Me (11a)]. The pK(a) values for the hydroxamic acid and the phenol moieties were determined for each member of the C-7 series. They correlated well with sigma in a linear free energy relationship (LFER) yielding values of rho = 0.71 (with sigma-p) for pK(a1) (the hydroxamic acid) and rho = 1.6 (with sigma-m) for pK(a2) (the phenol). A LFER also existed between the rate constants for the unimolecular decomposition of these hydroxamic acids to benzoxazolinones and sigma+ (rho = 1.1). The rates of hydroxamic acid reduction to lactams by beta-mercaptoethanol were also investigated. It was found that only compounds with electron-rich aromatic rings and specifically an oxa functionality para to the hydroxamic acid nitrogen atom (compounds 1 and 3-5) had measurable rates of reduction. H-1 NMR spectra recorded during this reaction in D2O buffers (pD9), however, showed that compounds 1, 2, 6-9 (the only ones investigated) formed a hemithioacetal at C-2 even though only 1 has a measurable rate of reduction by the same thiol. The remarkable rate enhancement provided by an oxa functionality suggests that reduction occurs by direct attack of thiolate on the hydroxamic nitrogen of a resonance-stabilized ion pair.
Completion of the Spectroscopical Data for the Synthesis of DIMBOA
作者:Norbert Handler、Thomas Erker
DOI:10.3797/scipharm.aut-05-08
日期:——
important role in the defense-system of plants against a variety of enemies. To investigate new mechanism and effects we synthesized the molecules using known synthetic pathways. Since the chemical data of DIMBOA are not complete or even false, we decided to publish the missing ones in this journal.
环状异羟肟酸,例如2,4-二羟基-7-甲氧基-2 H -1,4-苯并恶嗪-3(4 H)-1(DIMBOA)和2,4-二羟基-2 H -1,4-苯并恶嗪-3 (4 H)-1(DIBOA)被发现在几种植物中,在植物防御各种敌人的防御系统中起着重要作用。为了研究新的机理和作用,我们使用已知的合成途径合成了分子。由于DIMBOA的化学数据不完整甚至是虚假的,我们决定在此期刊上发表缺失的数据。