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T B Chen

Publications and source records attributed to T B Chen.

At least 19 recordsLinked to original sources
PubMed1996

Nitrogen-15 NMR chemical shifts in oligopeptides coordinated to cobalt(III).

Dipeptide, tripeptide, and tetrapeptide complexes with cobalt(III) ions were studied as model compounds for evaluation of 15N NMR chemical shifts induced in proteins upon binding transition metal ions. Coordination of oligopeptides to cobalt(III) resulted in large negative 15N NMR shifts for amine nitrogens (-76 to -32 ppm) and deprotonated amide nitrogens (-47 to -10). Coordination-induced shifts were affected by the nature of moiety at the trans position; the shifts were always larger with a carboxylato oxygen than with an amine nitrogen in the trans position. Thus, coordination-induced 15N NMR shifts provided direct and specific information on the stereochemistry of peptide coordination. Two new complexes, [Co(Gly-gly-gly-glyH(-3))(NH3)2] and Ba[Co(Gly-L-hisH(-2))(NO2)3], were synthesized and their structure was determined by NMR spectroscopy.

Amino Acid Sequence↗
PubMed1995

In vitro pharmacology of an angiotensin AT1 receptor antagonist with balanced affinity for AT2 receptors.

L-163,017 (6-[benzoylamino]-7-methyl-2-propyl-3-[[2'-(N-(3-methyl-1-butoxy) carbonylaminosulfonyl) [1,1']-biphenyl-4-yl]methyl]-3H-imidazo[4,5-b]pyridine) inhibited specific 125I-[Sar1, Ile8]angiotensin II binding to angiotensin AT1 receptor (Ki = 0.11-0.20 nM) in rabbit aorta, rat adrenal and human angiotensin AT1 receptor in CHO (Chinese hamster ovary transformed) cells and to AT2 receptor (Ki = 0.14-0.23 nM) in rat adrenal and brain receptors. L-163,017 also had a high affinity in the presence of bovine serum albumin (2 mg/ml), for angiotensin AT1 and AT2 receptors on human adrenal (Ki 3.9 and 4.3 nM), aorta (Ki 0.45 and 0.96 nM) and kidney (Ki 3.6 and 2.3 nM). The much higher Ki values in human tissues were likely due to the presence of bovine serum albumin in the binding assay buffer since L-163,017 had Ki values of 0.13 +/- 0.04 and 2.0 +/- 0.04 nM in the absence and presence of bovine serum albumin, respectively, in inhibiting 125I-[Sar1,Ile8]angiotensin II binding to angiotensin AT1 receptor in rat adrenal membranes. Scatchard analysis of 125I-[Sar1,Ile8]angiotensin II binding in the presence of bovine serum albumin (2 mg/ml) in rabbit aorta and bovine cerebellum indicated a competitive interaction of L-163,017 with angiotensin AT1 and AT2 receptors (Ki values 2.5 and 2.1 nM respectively). L-163,017 inhibited angiotensin II-induced aldosterone release in rat adrenal demonstrating that L-163,017 acted as a competitive antagonist (pA2 = 9.9) and lacked agonist activity. L-163,017 also inhibited angiotensin II responses in rat vascular tissues. The specificity of L-163,017 was shown by its lack of activity on the above functional responses produced by other agonists and in several binding assays.

Aldosterone↗
PubMed1995

Potent and orally active angiotensin II receptor antagonists with equal affinity for human AT1 and AT2 subtypes.

In order to block the effects induced by the interactions between angiotensin II (AII) and both AT1 and AT2 receptors, we have pursued the discovery of orally active non-peptide AII antagonists that exhibit potent and equal affinity for human AT1 and AT2 receptor subtypes. A series of previously prepared nanomolar (IC50) trisubstituted 1,2,4-triazolinone biphenyl-sulfonamide dual-acting AII antagonists has been modified at five different positions in order to increase AT2 binding affinity, maintain AT1 activity, and reduce the human adrenal AT2/AT1 potency ratio (IC50 ratio) from > or = 10. The targeted human adrenal potency ratio of < or = 1 was achieved with a number of compounds possessing an ethyl group at C5 of the triazolinone and a 3-fluoro substituent at the N4-biarylmethyl moiety. The most favored of these was compound 44 which exhibited subnanomolar potency at both the AT1 (rabbit aorta) and AT2 (rat midbrain) receptors, with a slight preference for the latter, and had a human adrenal AT2/AT1 IC50 ratio of 1. This tert-butyl sulfonylcarbamate with an N2-[2-bromo-5-(valerylamino)phenyl] substituent had excellent iv activity at 1 mg/kg (100% peak inhibition, > or = 4 h duration of action) and is orally active at 3 mg/kg with > 6 h duration of action in a conscious rat model. The present study shows that the NH of the amide on the N2-aryl moiety is not required for subnanomolar binding affinity to either receptor subtype, although a keto functionality at this position is essential for acceptable AT2 binding. Receptor-ligand binding interactions derived from the structure-activity relationships are discussed with respect to both receptor subtypes.

Administration, Oral↗
PubMed1995

Lipopolysaccharide core structures in Rhizobium etli and mutants deficient in O-antigen.

Lipopolysaccharide (LPS) is a major component of the bacterial outer membrane, and for Rhizobium spp. has been shown to play a critical role in the establishment of an effective nitrogen-fixing symbiosis with a legume host. Many genes required for O-chain polysaccharide synthesis are in the lps alpha region of the CE3 genome; this region may also carry lps genes required for core oligosaccharide synthesis. The LPSs from several strains mutated in the alpha region were isolated, and their mild acid released oligosaccharides, purified by high performance anion-exchange chromatography, were characterized by electrospray- and fast atom bombardment-mass spectrometry, NMR, and methylation analysis. The LPSs from several mutants contained truncated O-chains, and the core region consisted of a (3-deoxy-D-manno-2-octulosomic acid) (Kdo)-(2-->6)-alpha-Galp-(1-->6)-[alpha-GalpA-(1-->4)]-alpha-Ma np-(1-->5)- Kdop (3-deoxy-D-manno-2-octulosomic acid) (Kdo)pentasaccharide and a alpha-GalpA-(1-->4)-[alpha-GalpA-(1-->5)]-Kdop trisaccharide. The pentasaccharide was altered in two mutants in that it was missing either the terminal Kdo or the GalA residue. These results indicate that the lps alpha region, in addition to having the genes for O-chain synthesis, contains genes required for the transfer of these 2 residues to the core region. Also, the results show that an LPS with a complete core but lacking an O-chain polysaccharide is not sufficient for an effective symbiosis.

Carbohydrate Sequence↗
PubMed1995

Characterization of the binding of [125I]L-735,286: a new nonpeptide angiotensin II AT1 receptor radioligand.

[125I]L-735,286, a new potent and AT1-selective nonpeptide angiotensin II receptor radioligand, bound saturably to whole adrenal membranes. Scatchard and Hill plot analysis indicates a single class of high affinity (Kd = 0.5 nM) binding sites. The potencies of various angiotensin II agonists and antagonists in displacing specific [125I]L-735,286 binding are in good agreement with their potencies in displacing the binding of [125I]Sar1,Ile8-AII to adrenal AT1 receptors. The AT2 selective ligand, PD121981 had no effect on specific [125I]L-735,286 binding. In autoradiographic studies using rat kidney slices, specific labeling of [125I]L-735,286 was abolished by coincubation with saralasin. Collectively, the data indicated that [125I]L-735,286 represents a new, potent nonpeptide antagonist radioligand suitable for the study of angiotensin II AT1 receptors.

Angiotensin II↗
PubMed1994

Triazolinone biphenylsulfonamides as angiotensin II receptor antagonists with high affinity for both the AT1 and AT2 subtypes.

Angiotensin II (AII), the endogenous peptide ligand of the AII receptor, has equivalent high affinity for both the AT1 and AT2 receptor subtypes while most of the reported nonpeptide AII antagonists are AT1-selective. In an effort to identify dual AT1/AT2 nonpeptide AII antagonists, we have pursued modifications of previously prepared trisubstituted 1,2,4-triazolinone biphenylsulfonamides which exhibited subnanomolar in vitro AT1 (rabbit aorta) AII antagonism and AT2 (rat midbrain) IC50 values of < 40 nM. Present results show that a suitable amide (or reversed amide) side chain appropriately positioned on the N2-aryl group of these compounds gave > 15-fold enhancement in AT2 binding affinity without sacrificing nanomolar AT1 potency (IC50). This added amide, combined with an appropriate choice of the N-substituent on the sulfonamide and the ortho substituent on the N2-aryl group, led to an analogue (46, L-163,-007) which exhibited subnanomolar AT1 binding affinity and an AT2/AT1 IC50 ratio of 3. This compound showed excellent iv activity at 1 mg/kg and oral efficacy at 3 mg/kg with > 6 h duration in a conscious rat model. Available data suggest that the newly introduced amide side chain, mandatory for low nanomolar binding affinity at the AT2 receptor, is well-tolerated by the AT1 receptor and has minimal effect on the in vivo properties of these molecules.

Angiotensin II↗
PubMed1994

Somatostatin analogue octreotide modulates metabolism and effects of 5-fluorouracil and 5-fluorouridine in human colon cancer spheroids.

To examine if preferential retention of somatostatin analogues observed in some tumors might be used for modulation of effects of cancer drugs by co-treatment with long acting somatostatin analogues, the effects of somatostatin analogue octreotide on the kinetics of 5-fluorouracil (FUra) and 5-fluorouridine (FUrd) metabolism were studied by 19F NMR spectroscopy in multicell tumor spheroids comprised of human colon HT-29 adenocarcinoma cells. Octreotide stimulated the rate of formation of fluorouridinephosphates in FUra-treated cells, but inhibited this rate in FUrd-treated cells. Other elements of fluoropyrimidine metabolism were also altered by co-incubation with octreotide. A flow cytometric analysis indicated that FUra and FUrd arrested cells in the S phase, but co-treatment with octreotide almost eliminated the S-phase cells and induced the appearance of DNA fragments. These observations raise the possibility that somatostatin analogues can be used for specific modulation of fluoropyrimidine effects in tumors bearing somatostatin receptors.

Adenocarcinoma↗
PubMed1994

Triazolinone biphenylsulfonamide derivatives as orally active angiotensin II antagonists with potent AT1 receptor affinity and enhanced AT2 affinity.

Several series of 2,4-dihydro-2,4,5-trisubstituted-3H-1,2,4-triazol-3-ones with acidic sulfonamide replacements of tetrazole at the 2'-position of the biphenyl-4-ylmethyl side chain at N4 were prepared and tested as angiotensin II (AII) antagonists. Preferred substituents on the triazolinone ring were n-butyl at C5 and 2-(trifluoromethyl)phenyl at N2. Subnanomolar IC50 values at the AT1 receptor subtype were observed for a variety of acylsulfonamides, including aroyl, heteroaroyl, and cycloalkylcarbonyl derivatives. Certain other acidic sulfonamides, such as sulfonylcarbamates and disulfimides also displayed high affinity for the AT1 receptor. In addition, AT2 binding for some of these compounds was increased by as much as 1000-fold over the corresponding tetrazole (e.g., AT2 IC50 17 nM for the tert-butyl sulfonylcarbamate 92). When evaluated for inhibition of the AII pressor response, the benchmark benzoylsulfonamide 9 (L-159,913) was efficacious in several species and was superior to losartan (1a) in conscious rhesus monkeys. Several subsequent analogues, including the 2-chlorobenzoyl (18), (3-chlorothiophene-2-yl)carbonyl (51), ((S)-2,2-dimethylcyclopropyl)carbonyl (80), and tert-butoxycarbonyl (92) derivatives, were highly effective in rats, surpassing 9 and losartan in duration of action and/or potency. Compound 18 (L-162,223) displayed very prolonged AII antagonism in the rat model (> 24 h at 1 mg/kg iv). At 1 mg/kg po in rats, 18 and 92 (L-162,234) produced 85-87% peak inhibition of the AII pressor response with duration exceeding 6 h. The identification of triazolinone-based sulfonamide derivatives combining high AT1 affinity, considerably enhanced AT2 potency, and favorable in vivo properties provides insights relevant to the design of dual AT1/AT2 receptor antagonists.

Angiotensin II↗
PubMed1993

Non-peptide angiotensin II receptor antagonists. 1. Design, synthesis, and biological activity of N-substituted indoles and dihydroindoles.

A series of N-acylated indoles (12-18), N-alkylated indoles (19-24), N-acylated dihydroindoles (26-30), and N-alkylated dihydroindoles (31-34) were synthesized and evaluated in the in vitro AT1 (rabbit aorta) and AT2 (rat midbrain) binding assay. The carboxylic acid 3-[[N-(2-carboxy-3,6-dichlorobenzoyl)-5-indolyl]methyl]-5,7-dimeth yl- 2-ethyl-3H-imidazo[4,5-b]pyridine (14b) was found to be the most potent AT1 (IC50 = 0.8 nM) antagonist in the N-acylated indole series and displayed a 25-fold higher potency than the parent unsubstituted derivative 14a (AT1 IC50 = 20 nM) and a 22-fold greater potency than the corresponding dihydroindole analog 27 (AT1 IC50 = 18 nM). Replacement of the terminal carboxyl (COOH) of 14a with the bioisostere tetrazole in 16 (AT1 IC50 = 5 nM, AT2 IC50 = 130 nM) not only improved the AT1 potency by 4-fold but also resulted in a 50-fold increase in AT2 activity. In the N-alkylated indole series, the tetrazole 3-[[N-(2-tetrazol-5-yl-6-chlorobenzyl)-5- indolyl]methyl]-5,7-dimethyl-2-ethyl-3H-imidazo[4,5-b]pyridine (24) exhibited the highest AT1 (IC50 = 1 nM) activity, revealing a 230-fold increase in AT1 activity as a result of the incorporation of the isosteric tetrazole for the carboxyl (COOH) of 20 and a nearly 9-fold increase over the corresponding deschloro analog 22 (AT1 IC50 = 8.7 nM). Tetrazole 34 was identified as the most potent (AT1 IC50 = 18 nM) AT1 receptor antagonist in a structurally distinct series of compounds derived from N-alkylation of dihydroindole 25. A new class of highly potent (14b, AT1 IC50 = 0.8 nM; 24, AT1 IC50 = 1 nM) AT1-selective non-peptide AII receptor antagonists derived from N-substituted indoles and dihydroindoles is disclosed. Tetrazole 24 of the N-alkylated indole series displayed good in vivo activity by blocking the AII-induced pressor response for 5.5 h after intravenous administration in conscious normotensive rats at a 1.0 mg/kg dose level.

1-Sarcosine-8-Isoleucine Angiotensin II↗
PubMed1993

Non-peptide angiotensin II receptor antagonists. 2. Design, synthesis, and biological activity of N-substituted (phenylamino)phenylacetic acids and acyl sulfonamides.

The design, synthesis, and biological activity of a new class of highly potent non-peptide AII receptor antagonists derived from N-substituted (phenylamino)phenylacetic acids and acyl sulfonamides which exhibit a high selectivity for the AT1 receptor are described. A series of N-substituted (phenylamino)phenylacetic acids (9) and acyl sulfonamides (16) and a tetrazole derivative (19) were synthesized and evaluated in the in vitro AT1 (rabbit aorta) and AT2 (rat midbrain) binding assay. The (phenylamino)phenylacetic acids 9c (AT1 IC50 = 4 nM, AT2 IC50 = 0.74 microM), 9d (AT1 IC50 = 5.3 nM, AT2 IC50 = 0.49 microM), and 9e (AT1 IC50 = 5.3 nM, AT2 IC50 = 0.56 microM) were found to be the most potent AT1-selective AII antagonists in the acid series. Incorporation of various substituents in the central and bottom phenyl rings led to a decrease in the AT1 and AT2 binding affinity of the resulting compounds. Replacement of the carboxylic acid (CO2H) in 9c, 9d, and 9e with the bioisostere acyl sulfonamide (CONHSO2Ph) resulted in a (5-7)-fold increase in the AT1 potency of 16a (AT1 IC50 = 0.9 nM, AT2 IC50 = 0.2 microM), 16b (AT1 IC50 = 1 nM, AT2 IC50 = 2.9 microM), and 16c (AT1 IC50 = 0.8 nM, AT2 IC50 = 0.42 microM) and yielded acyl sulfonamides with subnanomolar AT1 activity. Incorporation of the acyl sulfonamide (CONHSO2Ph) for the CO2H of 9c not only enhanced the AT1 potency but also effected a marked increase in the AT2 potency of 16a (AT2 IC50 = 0.74 microM of 9c vs 0.2 microM of 16a) and made it the most potent AT2 antagonist in this study. Replacement of the CO2H of 9b with the bioisostere tetrazole resulted in 19 (AT1 IC50 = 15 nM) with a 2-fold loss in the AT1 and a complete loss in the AT2 binding affinity. (Phenylamino)phenylacetic acid 9c demonstrated good oral activity in AII-infused conscious normotensive rats at an oral dose of 1.0 mg/kg by inhibiting the pressor response for > 6 h. Acyl sulfonamides 16a-c displayed excellent in vivo activity by blocking the AII-induced pressor response for > 6 h after oral administration in conscious rats at a 3.0 mg/kg dose level. Both acyl sulfonamides 16a and 16c exhibited superior in vivo activity in rats compared to that of (phenylamino)phenylacetic acid 9c.

1-Sarcosine-8-Isoleucine Angiotensin II↗
PubMed1993

Nonpeptide angiotensin II antagonists derived from 1H-pyrazole-5-carboxylates and 4-aryl-1H-imidazole-5-carboxylates.

Two series of potential angiotensin II antagonists derived from carboxyl-functionalized "diazole" heterocycles have been prepared and evaluated. Initially, a limited investigation of 4-arylimidazole-5-carboxylates led to 2-n-butyl-4-(2-chlorophenyl)-1-[[2'-(1H-tetrazol-5-yl)biphenyl-4-y l] methyl]-1H-imidazole-5-carboxylic acid (12b), which was found to be a highly potent antagonist of the rabbit aorta AT1 receptor (IC50 0.55 nM). In conscious, normotensive rats, 12b at 0.1 mg/kg iv inhibited the pressor response to AII by 88%, with a duration of > 6 h. More extensively studied was an isosteric series of 3-alkyl-4-[[2'-(1H-tetrazol-5-yl)biphenyl-4-yl]methyl]-1H-pyrazole -5- carboxylates bearing aryl, alkyl, or aralkyl substituents at N1. These compounds were available in highly regioselective fashion via condensation of a substituted hydrazine hydrochloride with a 2-(methoxyimino)-4-oxoalkanoate intermediate. In vitro, the most potent pyrazolecarboxylic acids had n-butyl at C3 and were substituted at N1 by such groups as 2,6-dichlorophenyl (19h), 2-(trifluoromethyl)phenyl (19k), benzyl (19t), and phenethyl (19u), all with IC50 values of 0.18-0.24 nM. Although less potent in the receptor assay, 3-n-propylpyrazolecarboxylic acids were at least as effective as their butyl counterparts in vivo. Several of the pyrazolecarboxylic acid derivatives demonstrated potent, long-lasting oral activity in rats. At 1 mg/kg po, the 1-benzyl-3-butyl (19t), 1-(2,6-dichlorophenyl)-3-propyl (19v), 3-propyl-1-(2,2,2-trifluoroethyl) (19y), and 1-benzyl-3-propyl (19z) analogues all gave > or = 75% inhibition of the AII pressor response in the rat model, with duration of action > 23 h.

Angiotensin II↗
PubMed1993

Triazolinones as nonpeptide angiotensin II antagonists. 1. Synthesis and evaluation of potent 2,4,5-trisubstituted triazolinones.

A series of 2,4-dihydro-2,4,5-trisubstituted-3H-1,2,4-triazol-3-ones was prepared via several synthetic routes and evaluated as AII receptor antagonists in vitro and in vivo. The preferred compounds contained a [2'-(5-tetrazolyl)biphenyl-4-yl]methyl side chain at N4 and an n-butyl group at C5. A number of these bearing an alkyl or aralkyl substituent at N2 showed in vitro potency in the nanomolar range (rabbit aorta membrane receptor), and several of these, e.g., the 2,2-dimethyl-1-propyl analogue (54, IC50 = 2.1 nM), effectively blocked the AII pressor response in conscious rats with significant duration (2.5 h at 1 mg/kg orally for 54). Among analogues possessing aryl substituents at N2, ortho substitution on the phenyl moiety resulted in several derivatives with in vitro potency in the low nanomolar range. One of these, featuring a 2-(trifluoromethyl)phenyl substituent at N2 (25, IC50 = 1.2 nM), was effective at 1 mg/kg orally in the rat model, with a duration of > 6 h. Implications for hydrophobic and hydrogen-bonding interactions with the AT1 receptor are discussed.

Angiotensin II↗
PubMed1993

Nonpeptide angiotensin II antagonists derived from 4H-1,2,4-triazoles and 3H-imidazo[1,2-b][1,2,4]triazoles.

By a variety of synthetic routes, we have synthesized a series of 3,4,5-trisubstituted 4H-1,2,4-triazoles and a related series of 3H-imidazo[1,2-b][1,2,4]triazoles and evaluated them in vitro and in vivo as angiotensin II (AII) antagonists. Principal efforts focused on triazoles bearing an n-alkyl substitutent at C3 and a 4-[(2-carboxybenzoyl)amino]benzyl, (2'-carboxybiphenyl-4-yl)methyl, or [2'-(1H-tetrazol-5-yl)biphenyl-4-yl]methyl side chain at N4. Among numerous variations at C5, benzylthio groups gave the best potency. Particularly noteworthy was 3-n-butyl-5-[(2-carboxybenzyl)thio]-4-[[2'-(1H-tetrazol-5-yl )biphenyl-4 - yl]methyl]-4H-1,2,4-triazole (71, IC50 1.4 nM), which blocked the AII pressor response in conscious rats at 0.3 mg/kg iv with a duration of action of approximately 6 h, similar to that of DuP 753. Although 71 was active orally only at a 10-fold higher dose level, good oral bioavailability was demonstrated for a monoacidic analogue 62. Most potent among the bicyclic derivatives was 2-n-butyl-5,6-dimethyl-3-[[2'-(1H-tetrazol-5-yl)biphenyl-4-yl]meth yl]- 3H-imidazo[1,2-b][1,2,4]triazole (93, IC50 7.8 nM). The effects of hydrophobic, hydrogen-bonding, and ionic interactions with the AT1 receptor are considered.

Angiotensin II↗
PubMed1992

Characterization of the binding of [3H]L-158,809: a new potent and selective nonpeptide angiotensin II receptor (AT1) antagonist radioligand.

[3H]L-158,809, a new potent and AT1-selective nonpeptide angiotensin II receptor antagonist, bound saturably and reversibly to rat adrenal membranes. Scatchard and Hill plot analyses indicated a single class of high affinity (Kd = 0.66 nM) binding sites. The relative potencies of various angiotensin II-related peptide and nonpeptide antagonists in displacing [3H]L-158,809 binding correlated with their potencies in displacing the binding of 125I-Sar1,Ile8-angiotensin II to adrenal AT1 receptors. [3H]L-158,809 binding to adrenal membranes was not affected by addition of guanosine-5'-(beta,gamma-imido)triphosphate or various pharmacological agents known to interact with other common peptide and nonpeptide receptor systems. The potencies of angiotensin II receptor agonists, but not antagonists, in inhibiting specific [3H]L-158,809 binding were decreased in the presence of guanosine-5'-(beta,gamma-imido)triphosphate. Specific [3H]L-158,809 binding was also observed in rat liver and kidney. Collectively, the data indicate that [3H]L-158,809 represents a new, potent, nonpeptide, antagonist radioligand suitable for the study of angiotensin II AT1 receptors.

Adrenal Glands↗