Combinatorial modification of natural products: preparation of unencoded and encoded libraries of Rauwolfia alkaloids

We report the preparation of combinatorial libraries which consist of derivatives of the stereoisomeric alkaloids yohimbine and rauwolscine-members of the Rauwolfia genus. The chemistry was performed on solid support using the divide-and-pool method, and involved the derivatization of the E-ring carboxylates and hydroxyls of these alkaloids with 36 amino acids and 22 carboxylic acids, respectively, to afford 792 bifunctionalized derivatives. The rauwolscine library was prepared using an encoding strategy in which the identity of each incorporated amino acid was recorded by cosynthesizing chemically inert tags prior to the pooling step. The general strategy for library synthesis exploits existing functionality present on the natural products, and should be applicable to other families of secondary metabolites.

Versatile approach to encoding combinatorial organic syntheses using chemically robust secondary amine tags

Encoded combinatorial organic synthesis has recently emerged as a powerful tool for the discovery of biologically active compounds from complex chemical libraries. This report describes a new encoding methodology that uses chemically robust secondary amines as tags. These amines are incorporated into an N-[(dialkylcarbamoyl)methyl]glycine-coding oligomer through simple chemistry that is compatible with a wide range of polymer-supported transformations useful in combinatorial synthesis. In the decoding process acidic hydrolysis of the tagging polymer regenerates the secondary amines, which after dansylation are resolved and detected at sub-picomole levels by reversed-phase HPLC. The versatility of this strategy is demonstrated here by encoded syntheses of members of several representative heterocyclic compound classes, including beta-lactams, 4-thiazolidinones, and pyrrolidines.

A double-blind comparison of bisoprolol and atenolol in patients with essential hypertension

We compared the beta 1-selective adrenoceptor antagonists bisoprolol and atenolol in a double-blind, randomized crossover study. After 4 weeks placebo phase, 59 patients with essential hypertension received either 10 mg bisoprolol or 50 mg atenolol once daily for 8 weeks, increased if necessary (target BP < or = 150/90 mmHg) to 20 and 100 mg, respectively, after 4 weeks. After a second placebo phase, crossover occurred to the alternative drug. We measured resting systolic and diastolic blood pressures and heart rate at 24 h post-dose baseline and after 4 and 8 weeks treatment. Both drugs significantly lowered systolic and diastolic blood pressures and heart rate at 8 weeks compared to baseline (all p < 0.05). Bisoprolol reduced heart rate significantly more than atenolol (p < 0.01), but systolic and diastolic blood pressure changes were not different between the two drugs. There was no difference in patient acceptability of the drugs as assessed by visual analogue scale. Despite theoretical and circumstantial evidence to suggest superiority of bisoprolol over atenolol, no significant difference between the two was found except for greater heart rate reduction with bisoprolol.

A survey of magnetic fields in the dental operatory

Recently, there has been growing concern regarding the biological effects of occupational exposure to weak time-varying magnetic fields, especially those in the extremely low-frequency range (0.1-100.0 Hz). This study examined some potential sources and intensities of 60 Hz magnetic fields produced in the dental environment. A random sample of general dental offices and selected specialty offices was visited, and the magnetic fields associated with ultrasonic scalers, amalgamators, composite light curing units, X-ray view boxes and chair lights were measured. The median 60 Hz field strengths measured at various running speeds (off, standby, low and high) and the distances from the equipment (0, 15 and 30 cm) ranged from 1.2 to 2,225 milligauss (mG). Field strengths fell off quickly with distance, but were less affected by the running speed of the equipment. They also varied among the five types of equipment tested. This was likely due to variations in the make, model and age of the equipment. The 60 Hz magnetic field strengths recorded in the dental operatory were comparable to those reported from measurements of common household appliances. However, in view of recent concerns with respect to the possible effects of magnetic fields, it is suggested that exposures be minimized and the concept of prudent avoidance be employed.

Sequence specificity in the recognition of the epidermal growth factor receptor by the abl Src homology 2 domain

The transforming activity of the abl gene product requires a functional src homology 2 (SH2) domain. An assay was developed to evaluate this function by examining binding of a bacterially-expressed abl SH2 domain to the activated EGF receptor, used as a surrogate tyrosine phosphorylated protein. The sequence specificity of this interaction has been explored with a series of point mutants of EGF receptor. Analysis of equilibrium binding reveals that substitution of Tyr1086 for Phe in the EGF receptor produced a 10-fold reduced affinity for abl SH2 domain binding as compared to the wildtype receptor. Moreover, a phosphorylated peptide modeled on the sequences surrounding Tyr1086 specifically inhibits abl SH2 binding, with an IC50 of approximately 10 microM. Evaluation of a series of additional peptides, modeled on the Tyr1086 sequence, revealed that the carboxy terminal residues directly next to the phosphotyrosine were particularly critical to this binding. Molecular modeling studies of the pTyr1086 peptide revealed the potential hydrophobic, ionic and hydrogen bonding interactions involved in the functions of the abl SH2 domain.

Protein tyrosine phosphatase substrate specificity: size and phosphotyrosine positioning requirements in peptide substrates

The structural requirements of substrates for two recombinant protein tyrosine phosphatases (PTPases) are probed using various-sized synthetic phosphotyrosine (pY)-containing peptides corresponding to the autophosphorylation site in EGF receptor (EGFR) at Y992. The peptide EGFR988-998 (DADEpYLIPQQG) is chosen as a template due to its favorable kinetic constants. The contribution of individual amino acids on both sides of pY to binding and catalysis was assessed by kinetic analysis using a continuous, spectrophotometric assay. For both Yersinia PTPase and a soluble recombinant mammalian PTPase of 323 amino acid residues (rat PTP1), efficient binding and catalysis required six amino acids including the pY residue, i.e., four residues N-terminal to pY and one residue C-terminal to pY. Thus, PTPase substrate specificity is primarily dictated by residues to the N-terminal side of pY. The pY moiety and the rest of the peptide interact with PTPases in a cooperative manner. The presence of pY in the peptide substrate is necessary but not sufficient for high-affinity binding, since phosphotyrosine and other simple aryl phosphates exhibit weak binding, and dephosphorylated peptides do not bind to PTPases. Two variations on the pY moiety are also examined in order to assess their utility in PTPase inhibitor design. It is demonstrated that the thiophosphoryl analog in which one of the phosphate oxygens is replaced by sulfur can be hydrolyzed by PTPases, whereas the phosphonomethylphenylalanine analog in which the tyrosyl oxygen is replaced by a CH2 group is a competitive and nonhydrolyzable inhibitor, with Ki values of 18.6 and 10.2 microM, respectively, for the Yersinia PTPase and the rat PTP1.

Combination therapy with amlodipine and captopril for resistant systemic hypertension

This study was conducted to assess the therapeutic utility of combining amlodipine with captopril in patients with moderate-to-severe hypertension. Patients had hypertension of WHO grades I-III, with initial mean sitting and standing diastolic blood pressure of 100-119 mm Hg (phase V) after 2-4 weeks on placebo, and had remained uncontrolled (diastolic blood pressure > 95 mm Hg) despite a further 4 weeks on low-dose captopril. Twenty-nine patients entered the computer-randomized, double-blind, placebo-controlled, 2-way crossover comparison of either amlodipine 10 mg once daily or matching placebo added to continued therapy with captopril 25 mg twice daily for 4 weeks. Patients then acted as their own control and received the alternative amlodipine/placebo treatment plus their continued captopril therapy for another 4 weeks. Once-daily amlodipine was shown to be effective when combined with captopril. Mean baseline supine systolic blood pressure decreased from 167 to 149 mm Hg and standing systolic blood pressure from 167 to 144 mm Hg. Mean supine diastolic blood pressure decreased from 105 to 92 mm Hg, and standing diastolic blood pressure decreased from 110 to 96 mm Hg. The placebo-corrected amlodipine differences in mean changes from captopril baseline were -18/-12.2 mm Hg for supine and -20.1/-11.9 mm Hg for standing systolic and diastolic blood pressures, respectively (p < 0.001 for all 4 measurements). The most common side effects encountered with amlodipine were flushing and pedal edema. The combination of amlodipine and captopril was well tolerated, and no patient discontinued therapy. No significant treatment-related effects on biochemical and hematologic parameters were noted.

Measurement and management of cardiovascular risk factors--is screening worthwhile?

Coronary heart disease has been described as Scotland's national disease and ways of reducing its incidence are therefore of paramount importance especially in younger males. A recent British Medical Journal paper has indicated that general practitioners can make little impact on patients' lifestyles. This paper shows that a cohort of Scottish men (Social Class III-V) responded well (80%) to offers of screening for risk factors of CHD, continued to attend for review and showed highly significant changes in their risk factor profiles. A committed enthusiastic primary care team have shown the potential for reducing coronary risk factors in so-called healthy men.

The incidence of first-dose hypotension with quinapril in patients with mild to moderate hypertension

A total of 2242 patients with mild to moderate hypertension (diastolic pressure 95-120 mmHg) were randomised on a double-blind basis to receive a single dose of placebo, 5 mg quinapril or 10 mg quinapril. Patients were identified who: (a) met the blood pressure (BP) criteria for first-dose hypotension (sitting or standing systolic BP < 100 mmHg, or a fall in systolic BP > or = 20 mmHg on standing); (b) had symptoms suggestive of hypotension; and (c) met the BP criteria and had symptoms. In all three classifications there were no statistically significant differences between the incidences in placebo and combined active treatment groups, or between those in the two quinapril groups. No associated serious adverse events were reported. In the low-risk population studied, it would appear that the incidence of first-dose hypotension with quinapril is similar to placebo and is not dose-related.

Guidelines for resuscitation and transfer of patients with serious head injury

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Substrate specificity of the protein tyrosine phosphatases

The substrate specificity of a recombinant protein tyrosine phosphatase (PTPase) was probed using synthetic phosphotyrosine-containing peptides corresponding to several of the autophosphorylation sites in epidermal growth factor receptor (EGFR). The peptide corresponding to the autophosphorylation site, EGFR988-998, was chosen for further study due to its favorable kinetic constants. The contribution of individual amino acid side chains to the binding and catalysis was ascertained utilizing a strategy in which each amino acid within the undecapeptide EGFR988-998 (DADEpYLIPQQG) was sequentially substituted by an Ala residue (Ala-scan). The resulting effects due to singular Ala substitution were assessed by kinetic analysis with two widely divergent homogeneous PTPases. A "consensus sequence" for PTPase recognition may be suggested from the Ala-scan data as DADEpYAAPA, and the presence of acidic residues proximate to the NH2-terminal side of phosphorylation is critical for high-affinity binding and catalysis. The Km value for EGFR988-998 decreased as the pH increased, suggesting that phosphate dianion is favored for substrate binding. The results demonstrate that chemical features in the primary structure surrounding the dephosphorylation site contribute to PTPase substrate specificity.

A continuous spectrophotometric and fluorimetric assay for protein tyrosine phosphatase using phosphotyrosine-containing peptides

Two continuous assays for protein tyrosine phosphatases (PTPases) have been developed using phosphotyrosine containing peptide substrates. These assays are based on the marked differences in the spectra of the peptide before and after the removal of the phosphate group. The increase in the absorbance at 282 nm or the fluorescence at 305 nm of the peptide upon the action of PTPase can be followed continuously and the resulting progress curve (time course) can be analyzed directly using the integrated form of the Michaelis-Menten equation. The procedure is convenient and efficient, since both kcat and Km values can be obtained in a single run. The difference absorption coefficient (delta epsilon) at 282 nm is relatively insensitive to the pH of the reaction media. These techniques were applied to two homogeneous recombinant PTPases employing six phosphotyrosine-containing peptides. Km and kcat values obtained from the progress curve analysis were similar to those determined by the traditional initial rate inorganic phosphate assay. The peptides corresponding to autophosphorylation sites in Neu, p56lck, and p60src proteins show distinct behavior with the Yersinia PTPase, Yop51*, and the mammalian PTPase (PTP1U323). In both cases, the kcat values were relatively constant for all the peptides tested whereas the Km values were very sensitive to the amino acid sequence surrounding the tyrosine residue, especially in the case of Yop51*. Thus, both Yop51* and PTP1U323 show differential recognition of the phosphotyrosyl residues in the context of distinct primary structure of peptide substrates.

Cough and enalapril: assessment by spontaneous reporting and visual analogue scale under double-blind conditions

The incidence and prevalence of cough related to enalapril was assessed by spontaneous reporting and a visual analogue scale during a 6 month random double-blind parallel-group study comparing enalapril with nifedipine. Cough was reported spontaneously by 6.2% of enalapril-treated patients, and by none on nifedipine (NS). No patient had to discontinue enalapril because of cough. After 24 weeks treatment increases in visual analogue scale scores for cough frequency greater than or equal to 8 mm were more common for enalapril than nifedipine (difference 21.5%, 95% CI 7.3-35.7%). Increased cough frequency by visual analogue scale was present throughout the study in women, but less consistently in men. High scores for cough were not related to the dose of enalapril. Cough with enalapril was not an important problem during the 6 months of treatment. However increased cough frequency could be detected by visual analogue scale, with a frequency consistent with that observed in open clinic-based studies of longer duration. These findings suggest that ACE inhibitor-induced cough may increase in severity over time, and that even a period of 6 months treatment is too short to evaluate this side-effect adequately.

Doxazosin in 'resistant' hypertension

A study of doxazosin added to baseline therapy with a beta-adrenoceptor blocker plus a diuretic in the treatment of patients 'resistant' to the baseline therapy, showed that it was effective and generally well tolerated. The study was, however, open-label and lacked comparison with other third-line drugs.

Enalapril and nifedipine in the treatment of mild to moderate essential hypertension: a 6 month comparison

1. In a double-blind, randomised, parallel group study, 128 patients with sitting diastolic blood pressure between 95 and 125 mm Hg (Phase V) after 2-4 weeks run-in on placebo, received enalapril 10-40 mg once daily (65 patients) or nifedipine retard 10-40 mg twice daily (63 patients), utilising a double dummy technique. Dual target blood pressures were less than 150 mm Hg systolic and less than 90 mm Hg sitting diastolic. Inadequate responders had hydrochlorothiazide 12.5-50 mg once daily added. 2. The 3 h post-dose sitting blood pressures were lowered by 18/14 mm Hg (enalapril) and 20/14 mm Hg (nifedipine), but nifedipine gave greater standing reductions (16/13 mm Hg enalapril, 22/17 mm Hg nifedipine). The dual target blood pressures were achieved by 45% of those taking enalapril monotherapy and 43% of those taking nifedipine monotherapy. At the end of the hydrochlorothiazide phase the dual target pressures were achieved by 63% of the enalapril group and 56% of the nifedipine group. 3. Overall, 17 patients reported adverse events during the placebo run-in. During the active treatment-periods, 42 patients in the enalapril group experienced adverse events, as did 49 of those on nifedipine. Orthostatic effects were confined to those taking enalapril, whereas flushing/erythema, oedema and palpitations were more common in the nifedipine group. 4. Five patients in the enalapril and 14 in the nifedipine groups were withdrawn because of adverse events. One of those withdrawn on enalapril had angioneurotic oedema.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison of once daily atenolol, nitrendipine and their combination in mild to moderate essential hypertension

1. The aim of the study was to compare the efficacy and the tolerability of treatment with atenolol (50-100 mg once daily), nitrendipine (20-40 mg once daily) and their combination (atenolol 50 mg + nitrendipine 20 mg) once daily in patients with mild to moderate essential hypertension. 2. The study was a randomised, double-blind, placebo controlled parallel groups design: blood pressures were measured at 'trough' effect (i.e. 24 h after dosing) to assess the adequacy of once-daily treatment. 3. Mean blood pressures (mm Hg) recorded on four occasions over 12 weeks of treatment were significantly lower both with atenolol (155/97 sitting: 155/104 standing) and with the combination of atenolol plus nitrendipine (153/96 sitting: 152/104 standing) than with placebo (169/108 sitting: 169/114 standing). Nitrendipine alone had no significant effect on blood pressure 24 h after dosing (165/104 sitting: 165/110 standing). 4. Withdrawals due to adverse effects were more common during treatment with nitrendipine: 7/32 of the patients experienced adverse effects attributable to intense systemic vasodilatation (e.g., flushing, erythema, headache). 2/37 patients taking atenolol were withdrawn: one because he developed a psoriatic rash and the other because of impaired peripheral circulation. Of the 35 patients taking combination treatment, two were withdrawn: one developed headaches and dyspnoea, and the other asthma. 5. The results suggest that once daily dosing with nitrendipine does not control blood pressure throughout the 24 h period in the majority of patients, and is associated with a considerable burden of adverse effects. Combination treatment was better tolerated but appeared to offer no advantages over atenolol alone in terms either of blood pressure control or adverse effects.

The effects of indomethacin and sulindac upon the blood pressures of individuals with untreated labile or mild hypertension

Twelve patients (mean age 48.8 years, 5 females) with untreated labile or mild essential hypertension completed a randomised, double-blind crossover study comparing the effects of two-week courses of indomethacin, sulindac and matching placebo upon sitting and standing blood pressure. Both indomethacin and sulindac significantly increased systolic BP when compared with placebo; indomethacin tended to have a greater pressor effect than sulindac. During treatment with indomethacin, the mean BP rose from 136/86 to 149/92 (sitting), and from 136/93 to 150/99 standing. The extent of the pressor response was unrelated to baseline BP. The results indicate that both non-steroidal anti-inflammatory drugs (NSAIDs) have a significant pressor effect in individuals with untreated labile or mild hypertension. The fact that sulindac had a pressor effect implies that this response may be unrelated to inhibition of renal prostaglandins, or that the renal-sparing effect of sulindac is only relative. Extra-renal prostaglandins may play a role in the control of BP in this population. Individuals with labile or mild hypertension do not appear to exhibit exaggerated pressor responses during treatment with these NSAIDs, as similar increases in BP have been reported in normal subjects.

Comparison of the efficacy and acceptability of nicardipine and propranolol, alone and in combination, in mild to moderate hypertension

1. We evaluated the relative efficacies and tolerability of various low-dose combinations of nicardipine and propranolol in patients with mild-moderate essential hypertension (DBP Phase V of greater than 90-125 mmHg; WHO Grades I and II) in order to select the best one. 2. Sixty patients completed the double-blind, balanced, randomised three-way cross-over protocol, with each phase lasting 4 weeks, and in which twice daily nicardipine 40 mg or propranolol 80 mg was compared with four twice daily combinations of nicardipine (20 or 30 mg) plus propranolol (40 or 80 mg). 3. At 'peak' effect time (i.e., 2 h post-dosing) all four treatment combinations were significantly more effective than propranolol, with effects ranging from 9-23 mmHg (systolic) and 5-15 mmHg (diastolic). Only the two 30 mg nicardipine combinations with propranolol were more effective than nicardipine monotherapy, further reducing BP by 8-13 mmHg (systolic) and 5-7 mmHg (diastolic); there were no significant differences between them. 4. 'Trough' diastolic pressures were not different between treatments and 'trough' BP control was sub-optimal on all treatments. 5. 70% of patients on nicardipine monotherapy, 33% of those on propranolol monotherapy and 30% of patients during the placebo run-in complained of symptoms. In terms of complaint rates, there was little to choose between the four combinations (27-33%). Serum potassium and creatinine levels were elevated following propranolol monotherapy by 0.19 mmol 1-1 and 6.5 mumol 1-1 respectively (P less than 0.01 for both) and following the nicardipine 30 mg/propranolol 80 mg combination. Nicardipine monotherapy elevated serum T4 levels by an average of 0.57 ng dl-1 (P less than 0.05). 6. The twice daily combination of nicardipine 30 mg plus propranolol 40 mg was therefore the optimum one in terms of its efficacy and tolerability. Further studies need to be performed to test the hypothesis that a higher dose of propranolol might ameliorate troublesome vasodilator side effects. However, none of the treatments studied was ideal for clinical use in the twice daily dosage used in this study.

Quinapril: a double-blind, placebo-controlled trial in essential hypertension

Quinapril HCl is a novel, nonsulfhydryl angiotensin-converting enzyme (ACE) inhibitor. The Study Group evaluated its efficacy (20, 40, 80 mg daily with forced dose titration determination at trough blood pressure) once daily versus twice daily versus placebo, as well as its tolerability and safety, in 270 patients with mild to moderate essential hypertension (WHO Stages I and II, sitting diastolic blood pressure [DPB] greater than or equal to 95 mm Hg), for twelve weeks. Reductions in DBP of up to 13 mm Hg were obtained, and in full dosage more than 65% of patients achieved a reduction in DBP of 10 mm Hg or more from baseline or reduced their DBP to 90 mm Hg or less. Quinapril was well tolerated, and reported adverse effects were scarcely more frequent than in the placebo group. Once daily doses of quinapril were as safe and effective as twice-daily doses. Quinapril is likely to exhibit good therapeutic utility in the management of essential hypertension.