Modified Hantzsch Reaction Research Articles

Synthesis and voltage-clamp studies of methyl 1,4-dihydro-2, 6-dimethyl-5-nitro-4-(benzofurazanyl)pyridine-3-carboxylate racemates and enantiomers and of their benzofuroxanyl analogues.

Racemic methyl 1,4-dihydro-2, 6-dimethyl-5-nitro-4-(benzofurazanyl)pyridine-3-carboxylates (+/-)-10 and (+/-)-11 and their benzofuroxanyl analogues (+/-)-12 and (+/-)-13 were prepared using a modified Hantzsch reaction that involved the condensation of nitroacetone with methyl 3-aminocrotonate and the appropriate aldehydes. The racemic mixtures were resolved into the corresponding enantiomers. Whole-cell voltage-clamp studies on L-type Ca2+ channels expressed in a rat insulinoma cell line (RINm5F) showed that all the dextrorotatory antipodes were effective agonists of L-type Ca2+ currents, while the levorotatory ones were weak Ca2+ entry blockers. The (+)-enantiomer of benzofurazan-5'-yl derivative 11 demonstrated unusual activity in that, in addition to producing a potentiation of L-type currents, it interfered with the voltage-dependent gating of L-type channels by producing a net delay of their activation at low voltages. This compound represents an interesting tool to probe L-type Ca2+ channel structure and function.

Synthesis, rotamer orientation, and calcium channel modulation activities of alkyl and 2-phenethyl 1,4-dihydro-2,6-dimethyl-3-nitro-4-(3- or 6-substituted-2-pyridyl)-5-pyridinecarboxylates.

A group of racemic alkyl and 2-phenethyl 1,4-dihydro-2,6-dimethyl-3-nitro-4-(3- or 6-substituted-2-pyridyl)-5-pyridinecarboxylates (13a-q) was prepared using a modified Hantzsch reaction that involved the condensation of a 3- or 6-substituted-2-pyridinecarboxaldehyde (7a-j) with an alkyl or 2-phenethyl 3-aminocrotonate (11a-d) and nitroacetone (12). Nuclear Overhauser (NOE) studies indicated there is a significant rotamer fraction in solution where the pyridyl nitrogen is oriented above the 1,4-dihydropyridine ring, irrespective of whether a substituent is located at the 3- or 6-position. A potential H-bonding interaction between the pyridyl nitrogen free electron pair and the suitably positioned 1,4-dihydropyridine NH moiety may stablize this rotamer orientation. In vitro calcium channel antagonist and agonist activities were determined using guinea pig ileum longitudinal smooth muscle (GPILSM) and guinea pig left atrium (GPLA) assays, respectively. Compounds having an i-Pr ester substituent acted as dual cardioselective calcium channel agonists (GPLA)/smooth muscle-selective calcium channel antagonists (GPILSM), except for the C-4 3-nitro-2-pyridyl compound which exhibited an antagonist effect on both GPLA and GPILSM. In contrast, the compounds with a phenethyl ester group, which exhibited antagonist activity (IC50 = 10(-5)-10(-7) M range) on GPILSM, were devoid of cardiac agonist activity on GPLA. Structure-activity relationships showing the effect of a substituent (Me, CF3, Cl, NO2, Ph) at the 3- or 6-position of a C-4 2-pyridyl moiety and a variety of ester substituents (Me, Et, i-Pr, PhCH2CH2-) upon calcium channel modulation are described. Compounds possessing a 3- or 6-substituted-2-pyridyl moiety, in conjuction with an i-Pr ester substituent, are novel 1,4-dihydropyridine calcium channel modulators that offer a new drug design approach directed to the treatment of congestive heart failure and may also be useful as probes to study the structure-function relationships of calcium channels.

Synthesis and Calcium Channel-Modulating Effects of Alkyl (or Cycloalkyl) 1,4-Dihydro-2,6-dimethyl-3-nitro-4-pyridyl-5-pyridinecarboxylate Racemates and Enantiomers

A group of racemic alkyl (or cycloalkyl) 1,4-dihydro-2,6- dimethyl-3-nitro-4-(2-, 3-, or 4-pyridyl)-5-pyridinecarboxylate isomers (6-14) were prepared using a modified Hantzsch reaction that involved the condensation of nitroacetone with an alkyl (or cycloalkyl) 3-aminocrotonate and 2-, 3-, or 4-pyridinecarboxaldehyde. Determination of their in vitro calcium channel-modulating activities using guinea pig ileum longitudinal smooth muscle (GPILSM) and guinea pig left atrium (GPLA) assays showed that the 2-pyridyl isomers acted as dual cardioselective calcium channel agonists (GPLA)/smooth muscle selective calcium channel antagonists (GPILSM). In contrast, the 3-pyridyl and 4-pyridyl isomers acted as calcium channel agonists on both GPLA and GPILSM. In the C-4 2-pyridyl group of compounds, the size of the C-5 alkyl (or cycloalkyl) ester substituent was a determinant of GPILSM antagonist activity where the relative activity profile was cyclopentyl and cyclohexyl > t-Bu, i-Bu, and Et > MeOCH2CH2 > Me. The point of attachment of the C-4 pyridyl substituent was a determinant of GPLA agonist activity where the potency order was generally 4- and 3-pyridyl > 2-pyridyl. (+)-Cyclohexyl 1,4-dihydro-2,6-dimethyl-3-nitro-4-(2-pyridyl)-5- pyridinecarboxylate [(+)-14a] was a less potent calcium antagonist (IC50 = 5.27 x 10(-6) M) than the (-)-enantiomer (IC50 = 7.48 x 10(-8) M) on GPILSM. In the GPLA assay, (+)-14a exhibited a much more potent agonist effect (EC50 = 8.45 x 10(-6) M) relative to the marginal agonist effect produced by (-)-14a. The C-4 2-pyridyl compounds (enantiomers) constitute a novel type of 1,4-dihydropyridine calcium channel modulator that could provide a new drug design concept directed toward the treatment of congestive heart failure, and for use as probes to study the structure-function relationships of calcium channels.

Total synthesis of (+)-nostocyclamide 1

The synthesis of (+)-nostocyclamide from the oxazole 1 and thiazoles 2 and 3 is described. The oxazole amino ester 1b was prepared from N-protected alaninamide using a rhodium(II) catalysed N–H insertion reaction as a key step, and the thiazoles 2 and 3 were obtained using a modified Hantzsch reaction. The synthesis was completed in six further steps in which fragments 1 and 2 were coupled using mixed anhydride methodology to give the oxazole–thiazole 13, deprotection of which and coupling to 3 gave the linear bis-thiazole oxazole 15. Macrocyclisation using the pentafluorophenyl ester method gave (+)-nostocyclamide; the synthesis confirms that the natural product is the (+)-enantiomer and has the (2S,12R) absolute configuration.

Novel Hantzsch 1,4-dihydropyridines to study the structure-function relationships of calcium channels and photoinduced relaxation

A group of methyl 1,4-dihydro-2,6-dimethyl-4-(2-, 3- or 4-NHOH; 3- or 4-N=O)-phenyl-5-pyridinecarboxylates possessing a C-3 CO2Me or NO2 substituent [compounds 5–8, 10–12, below] were synthesized by reduction of the C-4 nitrophenyl precursors [1–4] to the corresponding phenylhydroxylamine [5–8] derivatives using 5% rhodium-on-charcoal with hydrazine hydrate as the hydrogen donor, followed by re-oxidation of the phenylhydroxylamine product [6–8] to the corresponding nitrosophenyl [10–12] derivative using pyridinium chlorochromate. A series of 1,4-dihydro-2,6-dimethyl-4-(2-trifluoromethylphenyl)pyridines [26–34] possessing CO2Me, COMe, CONH2, P(=O)OEt2, CN, NO2 C-3/C-5 substituents were synthesized using a modified Hantzsch reaction involving the condensation of 2-trifluoromethylbenzaldehyde [17] with an aminocrotonate [18–20] and a ketone [21–25] derivative. In vitro calcium channel (CC) activities were determined using a muscarinic-receptor-mediated Ca+2-dependent contraction of guinea pig ileal longitudinal smooth muscle assay. This class of compounds [5–8, 10–12, 26–34] exhibited weak CC antagonist activity [10–4 to 10–7 M range] relative to the reference drug nifedipine [IC50 = 1.4 × 10–8 M]. Structure–activity relationships [SARs] acquired were in agreement with known SARs where the relative potency order for C-4 phenyl substituents is ortho and meta > para. A C-3 nitro substituent decreased CC antagonist activity. Compounds 29–34 possessing C-3 CN or NO2, and a C-5 CO2Me, NO2, CONH2, COMe, or P(=O)OEt2, substituents exhibited weak CC antagonist activity in the 10–4 to 10–5 M range. Although this group of highly functionalized 1,4-dihydropyridines are not useful CC antagonists, they will serve as valuable model compounds to study the structure–function relationships of CC modulation. Drug Dev. Res. 42:120–130, 1997. © 1997 Wiley-Liss, Inc.

Synthesis and calcium channel modulating effects of isopropyl 1,4-dihydro-2,6-dimethyl-3-nitro-4-(thienyl)-5-pyridinecarboxylates.

A group of racemic isopropyl 1,4-dihydro-2,6-dimethyl-3-nitro-4-(thienyl)-5-pyridinecarboxylates++ + 7a-f were prepared using a modified Hantzsch reaction that involved the condensation of a thienylcarboxaldehyde 4a-f with isopropyl 3-aminocrotonate 5 and nitroacetone 6. In vitro calcium channel antagonist activities were determined using a guinea pig ileum longitudinal smooth muscle (GPILSM) assay. Compounds 7a-f exhibited weaker calcium channel antagonist activity (IC50 = 10(-5) to 10(-7) M range) than the reference drug nifedipine (IC50 = 1.43 x 10(-8) M). The point of attachment of the C-4 thienyl ring system was a determinant of antagonist activity [3-thienyl (7b) > 2-thienyl (7a)]. A 5-substituent in the 2-thienyl moiety influenced antagonist activity where the potency order was 5-bromo-2-thienyl 7f > or = 5-methyl-2-thienyl 7c > 2-thienyl 7a. Although the 5-methyl-2-thienyl 7c and 3-methyl-2-thienyl 7d isomers are equipotent antagonists, the 5-bromo-2-thienyl compound 7f appears to be marginally more active than the 4-bromo-2-thienyl isomer 7e. The 2-thienyl compound 7a, unlike the 3-thienyl isomer 7b, exhibited an agonist effect on GPILSM in the absence of the muscarinic agonist carbachol. Effects of the 2-thienyl 7a and 3-thienyl 7b isomers on the magnitude of calcium current were determined in guinea pig ventricular myocytes with voltage clamp techniques. Results showed that 2-thienyl 7a inhibited calcium current (antagonist) when voltage steps were made from a potential of -40 mV. However, when voltage steps were made from -60 mV, 7a enhanced calcium current (agonist). The 3-thienyl isomer 7b had little, if any, effect on calcium current.

Synthesis, biological evaluation, calcium channel antagonist activity, and anticonvulsant activity of felodipine coupled to a dihydropyridine-pyridinium salt redox chemical delivery system.

3-(2-Hydroxyethyl) 5-methyl 1,4-dihydro-2,6-dimethyl-4-(2,3-dichlorophenyl)-3,5-pyridinedi-carboxyla te (7) was prepared using a modified Hantzsch reaction, which was then elaborated to 3-[2-[[(1-methyl-1,4-dihydropyrid-3-yl)carbonyl]oxy]ethyl]5-methyl 1,4-dihydro-2,6-dimethyl-4-(2,3-dichlorophenyl)-3,5-pyridinedicarboxylat e [10, felodipine-chemical delivery system (CDS)]. The equipotent 3-(2-hydroxyethyl) 7 (IC50 = 3.04 x 10(-8) M) and felodipine-CDS (10, IC50 = 3.10 x 10(-8) M) were, respectively, 2- and 21-fold less potent calcium channel antagonists than the reference drugs nimodipine (IC50 = 1.49 x 10(-8) M) and felodipine (IC50 = 1.45 x 10(-9) M). Compounds 7, 10, nimodipine, and felodipine are highly lipophilic (Kp = 236, 366, 187, and 442, respectively). 3-(2-Hydroxyethyl) 7, felodipine-CDS (10), and felodipine provided protection against maximal electroshock-induced seizures in mice but were inactive in the subcutaneous metrazol anticonvulsant screen. In vitro incubation studies of felodipine with rat plasma and 20% brain homogenates showed felodipine was very stable in both biological media. Similar incubations of felodipine-CDS showed its rate of biotransformation followed psuedo-first-order kinetics with half-lives of 15.5 h in rat plasma and 1.3 h in 20% rat brain homgenates. In vivo biodistribution of felodipine and felodipine-CDS was studied. Uptake of felodipine in brain produced a peak brain concentration of 5 micrograms/g of brain tissue at 5 min, after which it rapidly egressed from brain resulting in undetectable levels at 60 min. Peak blood concentrations of 10 occurred at about 7 min followed by a rapid decline to a near undetectable concentration by 17 min. The pyridinium salt species 9, resulting from oxidation of 10, also reached peak concentrations at about 7 min but it slowly decreased to undetectable concentrations at 2 h. 3-(2-Hydroxyethyl) 7 remained at near undetectable concentrations throughout a 2 h time period. Localization of 10 in brain provided a peak concentration of 4.2 micrograms/g of brain tissue at 5 min and then decreased to negligible concentrations at 15 min. The concentration of oxidized pyridinium species 9 in brain remained high providing detectable concentrations up to 4 days. In contrast, the concentration of the 3-(2-hydroxyethyl) hydrolysis product 7 in brain remained at very low levels throughout the study. The slow hydrolysis rate of the pyridinium ester 9 to the 3-(2-hydroxyethyl) 7 and the rapid egression of felodipine-CDS from brain are believed to contribute to the moderate anticonvulsant activity exhibited hy the felodipine-CDS (10).

Reinvestigation of a modified Hantzsch thiazole synthesis

A recently reported modified Hantzsch reaction was reinvestigated and conditions were found to reach enantiomerically pure thiazole amino acid derivatives.

The Chiral Synthesis of Thiazole Amino Acid Enantiomers

Abstract An efficient modified Hantzsch reaction is described for the synthesis of optically pure thiazole amino acid derivatives from the corresponding amino acids. The method is exemplified by the synthesis of a derivative of L-(Gln)Thz, the novel chiral thiazole amino acid moiety of dolastatin 3. The Cotton effects of thiazole amino acids correlate well with the absolute stereochemistry of these compounds.

Synthesis of 14C‐ and 2H‐labeled (3S)‐1‐benzyl‐3‐pyrrolidinyl methyl (4S)‐2,6‐dimethyl‐4‐(m‐nitrophenyl)‐1,4‐dihydropyridine‐3,5‐dicarboxylate hydrochloride (YM‐09730‐5), a potent calcium antagonist

AbstractA potent and long acting calcium antagonist YM‐09730‐5, (3S)‐1‐benzyl‐3‐pyrrolidinyl methyl (4S)‐2,6‐dimethyl‐4‐(m‐nitrophenyl)‐1,4‐dihydropyridine‐3,5‐dicarboxylate hydrochloride (7a·HCl), was labeled with carbon‐14 and deuterium. The labeled materials were prepared by either the cyclizing Michael addition of 3‐aminocrotonate (5c) to benzylidene acetoacetate (6) or the modified Hantzsch reaction using m‐nitrobenzaldehyde, aminocrotonate(5a) and acetoacetate (3b). The 14C‐labeled material (7c·HCl) was synthesized from methyl [3‐14C]acetoacetate (4c) in a 32.0% radiochemical yield, at a specific activity of 60.9 mCi/mmol. The deuterium labeled material (7b·HCl) was synthesized from 1‐benzyl‐3‐hydroxypyrrolidine‐d4 (2b) which was obtained by the reduction of succinimide (1) with LiAlD4.

High-performance liquid chromatographic method for determining trichothecene mycotoxins by post-column fluorescence derivatization

The method described here is based on a separation of deoxynivalenol, nivalenol and fusarenon-X on a C 18 column using aqueous acetonitrile, and successive post-column fluorescence derivatization involving an alkaline decomposition to form formaldehyde and modified Hantzsch reaction with methyl acetoacetate and ammonium acetate (λ ex = 370 nm and λ em = 460 nm). By this method, 5–10 ng of the standard trichothecenes could be determined. By employing a clean-up procedure with a florisil column and a Sep-Pak CN cartridge, 61.4–96.9% recoveries were obtained for deoxynivalenol and nivalenol added to corn, wheat and barley at concentration levels of 0.05–1 ppm.

Analytical performance and comparability of the determination of triglycerides by 12 Lipid Research Clinic laboratories.

Twelve Lipid Research Clinic laboratories performed automated fluorometric triglyceride analyses on four control serum pools of known concentration by a modified Hantzsch reaction. The analyses were done during a two-year period, with use of common standards, methodology, and quality-control procedures. Estimates of analytical bias, variability, and short- and long-term trends for each instrument and for the entire group of LRC instruments are presented. High accuracy, precision, and interlaboratory comparability were achieved through rigorous standardization and control of the entire analytical procedure. Individual instrument biases varied from an average of 4.9% below to 1.0% above reference values. Between-run variability was often less than within-run variability and interlaboratory variation was substantially less than intralaboratory variation. The total standard deviation for all instruments ranged from 37 to 63 mg/liter. Only 5 to 14% of this variation was due to differences among instruments. The among-instruments standard deviation ranged from 12 to 17 mg/liter; the between-run, within-instrument standard deviation ranged from 29 to 46 mg/liter, and within-run standard deviation from 27 to 40 mg/liter. The significance of the results for long-term collaborative studies is discussed.