Design, synthesis and in vitro evaluation of a Dopa-organoboron compound that acts as a bladder relaxant through non-catecholamine receptors.

Bladder relaxation through drug administration is an interesting topic in medicinal and combinatorial chemistry. In fact, compounds targeting catecholamine receptors [dopamine receptors and beta-adrenergic receptors (ßAR) expressed in the bladder] are among the compounds commonly employed for this purpose. In particular, recent investigations have tended to focus on the ß3-adrenoceptor (ß3AR) as a target in the treatment of urinary incontinence and other disorders. However, organoboron compounds have been suggested as potent and efficient agents on these drug targets. In this work, through a docking study, we identified the parameters that induce a theoretical improvement in the affinity and activity of the organoboron compounds on the catecholamine receptors expressed in the bladder. Then, the identified potential drug, a boron-containing dopa-derivative named DPBX-L-Dopa, was synthesized and characterized. This compound induces a relaxation on the smooth muscle of the rat bladder, behaving as a weak relaxant compared to isoproterenol but with similar efficacy to BRL377, a selective ß3AR agonist. However, unexpectedly, this effect was not blocked by propranolol or haloperidol at the concentrations at which they are able to block the catecholamine receptors in bladder tissue. In view of these results, the effect of DPBX-L-Dopa compound on the alpha 1 adrenergic receptors (α1AR) of aorta of the rats was also explored; however, no response of the tissue to this compound was obtained. The possible mechanisms of the action of this compound were explored and are discussed further.

Homoisoflavonoids and Chalcones Isolated from Haematoxylum campechianum L., with Spasmolytic Activity.

Haematoxylum campechianum is a medicinal plant employed as an astringent to purify the blood and to treat stomach problems such as diarrhea and dysentery. A bio-guided chemical fractionation of the methanolic extract obtained from this plant allowed for the isolation of five compounds: two chalcones known as sappanchalcone (1); 3-deoxysappanchalcone (2); three homoisoflavonoids known as hematoxylol A (3); 4-O-methylhematoxylol (4); and, hematoxin (5). The spasmolytic activity was determined in an in vitro model (electrically induced contractions of guinea pig ileum), and allowed to demonstrate that the methanolic extract (EC50 = 62.11 ± 3.23) fractions HcF7 (EC50 = 61.75 ± 3.55) and HcF9 (EC50 = 125.5 ± 10.65) and compounds 1 (EC50 = 16.06 ± 2.15) and 2 (EC50 = 25.37 ± 3.47) of Haematoxylum campechianum present significant relaxing activity as compared to papaverine (EC50 = 20.08 ± 2.0) as a positive control.

Spasmolytic Action of Preparations and Compounds from Hofmeisteria schaffneri.

Hofmeisteria schaffneri is used in Mexican folk medicine for treating painful gastric complaints. Therefore, in this paper the smooth muscle relaxant effect of the essential oil, and an infusion of the whole plant were evaluated using the gastrointestinal transit test in mice. The results revealed that both preparations at 316 mg/kg inhibited gastrointestinal transit by 47.5 and 52.1%, respectively. The common component of the infusion and essential oil was 8.9 -epoxy-10-acetoxythymol angelate (2), which inhibited the gastrointestinal transit by 53.4% at a dose of 31.6 mg/kg. An HPLC-UV method was developed and validated to quantify 2. The chromatographic conditions were: A LiChrospher® 100 RP-18 column (250 x 4 mm i.d., 5µm) with a mobile phase composed of CH3CN-H2O, in a gradient run at a flow rate of 0.6 mL/min, using a wavelength of 215 nm. The method was linear, precise, accurate, and showed excellent recovery. According to the results, compound 2 can be used as a marker for the quality control procedures of the crude drug of H. schaffneri.

Antispasmodic Effects and Action Mechanism of Essential Oil of Chrysactinia mexicana A. Gray on Rabbit Ileum.

The Chrysactinia mexicana A. Gray (C. mexicana) plant is used in folk medicine to treat fever and rheumatism; it is used as a diuretic, antispasmodic; and it is used for its aphrodisiac properties. This study investigates the effects of the essential oil of C. mexicana (EOCM) on the contractility of rabbit ileum and the mechanisms of action involved. Muscle contractility studies in vitro in an organ bath to evaluate the response to EOCM were performed in the rabbit ileum. EOCM (1-100 µg·mL(-1)) reduced the amplitude and area under the curve of spontaneous contractions of the ileum. The contractions induced by carbachol 1 µM, potassium chloride (KCl) 60 mM or Bay K8644 1 µM were reduced by EOCM (30 µg·mL(-1)). Apamin 1 µM and charybdotoxin 0.01 µM decreased the inhibition induced by EOCM. The d-cAMP 1 µM decreased the inhibition induced by EOCM. l-NNA 10 µM, Rp-8-Br-PET-cGMPS 1 µM, d,l-propargylglycine 2 mM, or aminooxyacetic acid hemihydrochloride 2 mM did not modify the EOCM effect. In conclusion, EOCM induces an antispasmodic effect and could be used in the treatment of intestinal spasms or diarrhea processes. This effect would be mediated by Ca(2+), Ca(2+)-activated K⁺ channels and cAMP.

Essential oil from the leaves of Xylopia langsdorfiana (Annonaceae) as a possible spasmolytic agent.

Xylopia langsdorfiana A. St.-Hil. &Tul. (Annonaceae) is popularly known in the northeast of Brazil as 'pimenteira da terra', and an essential oil (XL-OE) was extracted from its leaves. Since Xylopia species are cited in folk medicine and diterpenes from X. langsdorfiana have spasmolytic activity, this study aimed to investigate a possible spasmolytic action of XL-OE on smooth muscle models. XL-OE (243 and 729 µg/mL) showed low pharmacologic efficacy on guinea pig trachea and rat aorta and uterus. However, in guinea pig ileum, XL-OE (27-729 µg/mL) inhibited carbachol or histamine-induced phasic contractions (1 µM) in a significant and concentration-dependent manner. In addition, XL-OE (81 µg/mL) reduced fluorescence intensity in ileal myocytes stimulated by histamine, indicating a decrease in cytosolic calcium concentration, which could explain the spasmolytic activity. Thus, XL-OE proved to be a promising natural product to be used in gastrointestinal diseases acting by modulating the cytosolic calcium concentration.

Antispasmodic effects and composition of the essential oils from two South American chemotypes of Lippia alba.

ETHOPHARMACOLOGY RELEVANCE: Lippia alba (Mill.) N. E. Brown (Verbenaceae) is an aromatic species used in Central and South America as eupeptic for indigestion. In Argentina, it is used by the "criollos" from the Chaco province. There are several chemotypes which differ in the chemical composition of the essential oils. Nowadays, it is experimentally cultivated in some countries of the region, including Argentina. AIM OF THE STUDY: To compare the chemical composition and pharmacology of the essential oils from two chemotypes: "citral" (CEO) and "linalool" (LEO), in isolated rat duodenum and ileum. METHODS: Contractile concentration-response curves (CRC) of acetylcholine (ACh) and calcium in 40mM K(+)-medium (Ca(2+)-CRC) were done in isolated intestine portions, in the absence and presence of CEO or LEO at different concentrations. RESULTS: Likewise verapamil, CEO and LEO induced a non-competitive inhibition of the ACh-CRC, with IC50 of 7.0±0.3mg CEO/mL and 37.2±4.2mg LEO/mL. l-NAME, a NO-synthase blocker, increased the IC50 of CEO to 26.1±8.7mg CEO/mL. Likewise verapamil, CEO and LEO non-competitively inhibited the Ca(2+)-CRC, with IC50 of 6.3±1.7mg CEO/mL, 7.0±2.5mg LEO/mL and 0.24±0.04mg verapamil/mL (pIC50: 6.28). CEO was proved to possess limonene, neral, geranial and (-)-carvone as the major components, while LEO was rich in linalool. CONCLUSIONS: Results suggest that CEO has five times more potency than LEO to inhibit muscarinic contractions. The essential oils of both chemotypes interfered with the Ca(2+)-influx, but with an IC50 about 28 times higher than that of verapamil. Moreover, CEO partially stimulated the NO production. These results show the medicinal usefulness of both Lippia alba chemotypes, thus validating its traditional use, potency and mechanism of action.

Relaxant effects of Artemisia ludoviciana on isolated rat smooth muscle tissues.

ETHNOPHARMACOLOGICAL RELEVANCE: Artemisia ludoviciana spp. mexicana (Willd. Ex.) Spring D.D. Keck (Asteraceae), known as "estafiate" is employed for the treatment of diarrhea, dysentery, parasites, abdominal pain, vomiting, stomach ache, and also as antispasmodic agent. The aim of the present study was to evaluate the relaxant effect of hexanic (HEAl), dichloromethanic (DEAl) and methanolic (MEAl) extracts on isolated trachea, ileum and aorta rat rings, and to establish the tracheo-relaxant mode of action of DEAl. MATERIALS AND METHODS: All extracts were investigated based on their capacity of to inhibit the rat ileum spontaneous contraction, to relax contraction induced by noradrenaline (0.1 µM) on endothelium-intact and endothelium-denuded thoracic aorta rat rings, and also to inhibit contraction provoked by carbachol (1 µM) on rat trachea. RESULTS: Organic extracts had no spasmolytic action on ileum strips compared to positive control (papaverine, p<0.05). On the other hand, all extracts induced a significant concentration- and partial endothelium-dependent vasorelaxant activity. Extracts also showed significant relaxant effect on pre-contracted tracheal tissue in a concentration-dependent manner. In last two experiments, DEAl was the most potent and efficient extract; however, it was less potent than papaverine and theophylline, used as positive controls (p<0.05). In tracheal preparation, DEAl shifted to the right, in a parallel manner, the concentration-response curves induced by carbachol (p<0.05). Also, DEAl induced a significant relaxant effect on the contraction produced by potassium chloride (KCl, 80 mM). Pre-incubation with 1-H-[1,2,4]-oxadiazolo-[4,3a]-quinoxalin-1-one (ODQ, 10 µM), indomethacin (10 µM), N(ω)-nitro-L-arginine methyl ester (L-NAME, 10 µM), glibenclamide (10 µM) and 2-aminopyridine (2-AP, 100 µM) did not modify the DEAl-relaxant curves. CONCLUSIONS: Functional experiments suggest that the most active extract, DEAl, induced its relaxant effect by possible muscarinic receptors antagonism and calcium channel blockade in tracheal rings. On the other hand, significant vasorelaxant activity showed by DEAl is partially endothelium-dependent. Finally, spasmolytic activity induced by the extracts in the rat ileum was not significant, which suggests that the antidiarrheic effect of the plant is related to antimicrobial and antiparasitic properties previously described.

Spasmolytic activity of Rosmarinus officinalis L. involves calcium channels in the guinea pig ileum.

ETHNOPHARMACOLOGICAL RELEVANCE: Rosmarinus officinalis L. is a plant used around the world for its properties to cure pain in several conditions, such as arthritic and abdominal pain or as an antispasmodic; however, there are no scientific studies demonstrating its spasmolytic activity. Therefore, the aim of the present study was to investigate the effect of an ethanol extract from Rosmarinus officinalis aerial parts and the possible mechanism involved by using rings from the isolated guinea pig ileum (IGPI). MATERIALS AND METHODS: The IGPI rings were pre-contracted with potassium chloride (KCl; 60 mM), acetylcholine (ACh; 1 × 10(-9) to 1 × 10(-5)M) or electrical field stimulation (EFS; 0.3 Hz of frequency, 3.0 ms of duration and 14 V intensity) and tested in the presence of the Rosmarinus officinalis ethanol extract (150, 300, 600 and 1 200 µg/mL) or a referenced smooth muscle relaxant (papaverine, 30 µM). In addition, the possible mechanism of action was analyzed in the presence of hexametonium (a ganglionic blocker), indomethacine (an inhibitor of prostaglandins), l-NAME (a selective inhibitor of the nitric oxide synthase) and nifedipine (a calcium channel blocker). RESULTS: Rosmarinus officinalis ethanol extract exhibited a significant and concentration-dependent spasmolytic activity on the contractions induced by KCl (CI(50) = 661.06 ± 155.91 µg/mL); ACh (CI(50) = 464.05 ± 16.85 µg/mL) and EFS (CI(50) = 513.72 ± 34.13 µg/mL). Spasmolytic response of Rosmarinus officinalis (600 µg/mL) was reverted in the presence of nifedipine 1 µM, but not in the presence of hexamethonium 0.5mM, indomethacine 1 µM or L-NAME 100 µM. CONCLUSION: The present results reinforce the use of Rosmarinus officinalis as antispasmodic in folk medicine. Moreover, it is demonstrated the involvement of calcium channels in this activity, but not the participation of nicotinic receptors, prostaglandins or nitric oxide.

Synthesis, biological evaluation, and docking studies of gigantol analogs as calmodulin inhibitors.

Several analogs of gigantol (1) were synthesized to evaluate their effect on the complexes Ca(2+)-calmodulin (CaM) and Ca(2+)-CaM-CaM sensitive phosphodiesterase 1 (PDE1). The compounds belong to four structural groups including, 1,2-diphenylethanes (2-11), diphenylmethanes (13-15), 1,3-diphenylpropenones (16-18), and 1,3-diphenylpropanes (20-22). In vitro enzymatic studies showed that all compounds except 11 inhibited the complex Ca(2+)-CaM-PDE1 with IC(50) values ranging from 9 to 146 µM. On the other hand, all analogs but 11, 12 and 15 quenched the extrinsic fluorescence of the CaM biosensor hCaM-M124C-mBBr to different extent, then revealing different affinities to CaM; their affinity constants (K(m)) values were in the range of 3-80 µM. Molecular modeling studies indicated that all these compounds bound to CaM at the same site that the classical inhibitors trifluoperazine (TFP) and chlorpromazine (CPZ). Some of these analogs could be worthy candidates for developing new anti-tumor, local anesthetics, antidepressants, antipsychotic, or smooth muscle relaxant drugs, with anti-CaM properties due to their good affinity to CaM and the straightforwardness of their synthesis. In addition they could be valuable tools for the study of Ca(2+)-CaM functions.

Solving the confusion of gnaphaliin structure: gnaphaliin A and gnaphaliin B identified as active principles of Gnaphalium liebmannii with tracheal smooth muscle relaxant properties.

Inflorescences of Gnaphalium liebmannii, commonly known as "Gordolobo", is the most important remedy in Mexican traditional medicine to treat respiratory diseases, including asthma. By a bioguided fractionation of the n-hexane extract of this plant, following the relaxant effect on guinea pig tracheal smooth muscle, the flavones 5,7-dihydroxy-3,8-dimethoxyflavone (1) and 3,5-dihydroxy-7,8-dimethoxyflavone (2) were identified as the active relaxant compounds. Compounds 1 and 2 showed more potent relaxant properties than aminophylline in this model. Both 1 and 2 have been described as gnaphaliin in the past; here EIMS data, NMR experiments for both compounds, and X-ray diffraction analysis for 1 provided structural information to suggest that 1 and 2 should be named gnaphaliins A and B, respectively.

Relaxant and antispasmodic effects of extracts of the orchid Encyclia michuacana on isolated guinea pig ileum.

The antispasmodic effects of hexane-, chloroform-, methanol- and water-extracts of the orchid Encyclia michuacana were studied in vitro on guinea pig ileum against three spasmogens: acetylcholine (Ach), histamine and barium chloride. The chloroform extract exerted a significant antispasmodic effect on ileum contractions induced by Ach, histamine and barium chloride (IC(50) = 90.64, 73.12 and 115.2 microg/mL, respectively). Furthermore, the chloroform extract of E. michuacana provoked a concentration-dependent inhibition of spontaneous contractions of guinea pig ileum with potencies comparable to those of papaverine. The antagonism against the spasmogens used suggests that the action of the chloroform extract of E. michuacana could be due mainly to the presence of gigantol. Hexane-, methanol- and water-extracts did not elicit any significant spasmolytic activity.

Chemical composition and antispasmodic effect of Casimiroa pringlei essential oil on rat uterus.

The Casimiroa pringlei essential oil was analyzed to determine its chemical composition. Its effect on rat uterine smooth muscle was studied and compared with verapamil. Pure commercial piperitone, eucalyptol, and alpha-terpineol, the major constituents of C. pringlei essential oil, were tested on the uterine tonic contraction induced by high-potassium depolarizing solution (KCl 60 mM).

Spasmolytic effect of constituents from Lepechinia caulescens on rat uterus.

Lepechinia caulescens Ortega Epling (Lamiaceae) is a perennial herb used in Mexican folk medicine to treat diabetes, hypertension, gastrointestinal infections, dysmenorrhea and as abortifacient. In this study, a bioassay-guided fractionation of the hexanes extract of the leaves, evaluating the capacity to relax contraction of rat uterus rings induced by KCl (60mM), was made. The results indicated that, from the four isolated terpenes, spathulenol (1) was the most potent spasmolytic agent, followed by methyl 9alpha,13alpha-epidioxyabiet-8(14)-en-18-oate (2), 9alpha-hydroxydehydroabietyl alcohol (4) and dehydroabietic acid (3) studied at 10 and 30 microg/mL. The spasmolytic activity of 1 was totally reverted by addition of increasing extracellular Ca2+ concentrations ([Ca2+]o), while incubation of uterus rings with 1 in calcium free solutions reduced the contraction produced by [Ca2+]o in a concentration-dependent manner. Moreover, the presence of L-NAME (100 microM) or propranolol (10 microM) did not block the spasmolytic effect. These results suggest that 1 induces a greater blocking action on voltage-operated calcium channels. EtOAc and MeOH extracts of the leaves, which showed slight relaxing activity, led to 4 and rosmarinic acid (5).

Synthesis and antispasmodic activity of lidocaine derivatives endowed with reduced local anesthetic action.

The present structure-activity relationship (SAR) study focused on chemical modifications of the structure of the local anesthetic lidocaine, and indicated analogues having reduced anesthetic potency, but with superior potency relative to the prototype in preventing anaphylactic or histamine-evoked ileum contraction. From the SAR analysis, 2-(diethylamino)-N-(trifluoromethyl-phenyl) and 2-(diethylamino)-N-(dimethyl-phenyl) acetamides were selected as the most promising compounds. New insights into the applicability of non-anesthetic lidocaine derivatives as templates in drug discovery for allergic syndromes are provided.

QSAR study on the relaxant agents from some Mexican medicinal plants and synthetic related organic compounds.

Quantitative Structure-Activity Relationship studies were performed to describe and predict the antispasmodic activity of some molecules isolated from Mexican Medicinal Flora as well as for some synthetic ones based on stilbenoid bioisosteres. The relaxant activity of these molecules was taken from experiments on rat and guinea-pig ileum tissues. Given that there is some evidence of species-specific on the relaxant effects, two data sets were proposed, one for rat ileum and the other for guinea-pig ileum. These data were statistically treated in order to find a Quantitative Structure-Activity Relationship model that could describe the corresponding biological models. The goodness of prediction for the best models was measured in terms of the Leave-One-Out Cross-Validation R(2) (LOO q(2)) and the correlation coefficients of regressions through the origin (RTO R(2)0). Results show that papaverine activity could not be used as reference in rat ileum tests; however, this molecule can be used as a good reference molecule in guinea-pig ileum tests. Our study shows that MATS5p and R8m+ descriptors are the most important descriptors in predicting the rat ileum activity and that atomic polarizability is the main atomic property. On the other hand, the R3u GETAWAY descriptor turns out to be important in predicting the guinea-pig ileum activity where the influence/distance of substituents on these molecules could describe the observed activity.

The spasmolytic effect of Aloysia citriodora, Palau (South American cedrón) is partially due to its vitexin but not isovitexin on rat duodenums.

The spasmolytic effects of an acqueous extract of cedrón (AEC) were studied on rat isolated duodenums. This plant (Aloysia citriodora Palau, Verbenaceae) is widely used for gastrointestinal disorders and as eupeptic in South America. AEC non-competitively inhibited the dose-response curve (DRC) of Ach (IC50 of 1.34 +/- 0.49 mg lyophilized/mL) and the DRC of Ca(2+) in high-[K(2-)](o) (IC50 of 2.64 +/- 0.23 mg/mL). AEC potentiated the non-competitive inhibition of either 30 micromol/L W-7 (a calmodulin blocker) and 5-15 micromol/L papaverine on the Ca(2+)-DRC. Also, AEC relaxed the contracture produced by high-[K(+)](o) (IC50 of 2.6 +/- 0.2 mg/mL) until 81.0 +/- 3.2% of the maximal effect of papaverine and 78.1+/- 5.0% of the quercetin, the most selective inhibitor of PDE. The AEC relaxation was non-competitively inhibited by 10-30 micromol/L methylene blue and competitively antagonized by 40 mmol/L TEA. The relaxation of 1mg/mL AEC was inhibited by hypoxia, but not that of 2mg/mL. Two flavonoids were identified by HPLC in the AEC: vitexin and isovitexin. Vitexin non-competitively inhibited the Ach-DRC (pD(2') of 5.7 +/- 0.4) but significantly run leftward the DRC of Ca(2+). Isovitexin did not significantly inhibit the DRC of Ach nor Ca(2+). The results suggest that the spasmolytic effect of AEC could be mostly associated to the increase in cGMP (target shared with the PDE inhibitors) and the activation of K(+)-channels. At low concentrations, AEC also inhibits the aerobic metabolism. The flavonoid vitexin is partially responsible for the effect, since it non-competitively inhibits Ach but not the Ca(2+) influx. Isovitexin was devoid of activity on duodenums.

Constituents, biological activities and quality control parameters of the crude extract and essential oil from Arracacia tolucensis var. multifida.

Bioassay guided fractionation of an antimycobacterial extract of Arracacia tolucensis var. multifida (Umbelliferae) led to the isolation of isoimperatorin (1), osthol (2), suberosin (3), 8-methoxypsoralen (8-MOP) (4), herniarin (5), scoparone (6), umbelliferone (7), dihydroxypeucedanin (8), 5-methoxypsoralen (5-MOP) (9), isoscopoletin (10) and scopoletin (11). The isolates were tested against Mycobacterium tuberculosis and only 1-4 showed significant activity with MIC values of 64, 32, 16 and 128 microg/mL, respectively. The essential oil showed moderate in vitro antibacterial activity against representative Gram-positive and Gram-negative bacteria. The volatile oil of Arracacia tolucensis var. multifida was analyzed by GC-MS and found to be composed mainly by 2 and 3. The essential oil (IC(50)=116.4+/-23.2 microg/mL) and the extract (IC(50)=1153.1+/-53.2 microg/mL) of the plant provoked concentration dependent inhibition of the tone and amplitude of the guinea-pig ileum spontaneous contractions; the latter activity was related with the high coumarin content of this species. A suitable (novel and rapid) HPLC method to quantify the major active coumarins of the plant was developed. The method provides also a reproducible fingerprint useful for identity tests of this plant.

Mikania laevigata syrup does not induce side effects on reproductive system of male Wistar rats.

Mikania laevigata (Asteraceae) is a native plant from South America and popularly used as antispasmodic and to treat respiratory diseases. Coumarin is the major chemical substance found in this plant, which have been shown to have antifertility activity in female rats. This study evaluates the toxicity of the exposure to the Mikania laevigata syrup using coumarin as chemical marker on reproductive endpoints in male Wistar rats. Endpoints including reproductive organs weight, sperm and spermatids numbers and sperm morphology were evaluated. Animals were treated daily with Mikania laevigata syrup (3.5; 7.0 and 14.0mg/kg of coumarin) during 90 days by oral gavage. No alterations were observed in body and organ weights, sperm and spermatids numbers as well as sperm morphology of the male rats after the exposure to the Mikania laevigata syrup. Results therefore suggest absence of male reproductive toxicity of the Mikania laevigata syrup at tested doses.

Molecular structure and QSAR study on antispasmodic activity of some xanthoxyline derivatives.

Semi-empirical molecular orbital calculations at AM1 level were done with the aim to investigate the structure-activity relationships of antispasmodic activities of ten 2-(X-benzyloxy)-4,6-dimethoxyacetophenones with X = H, 4'-F, 4'-NO2, 4'-CH3, 4'-Cl, 3',4'-(CH3)2, 4'-OCH3, 4'-Br, 4'-OCH2C6H5, and 4'-C(CH3)3, against acetylcholine-induced contraction of the guinea pig ileum. The most significant quantum chemical descriptors for this series of compounds were the net atomic charges, nucleophilic and electrophilic frontier electron density, HOMO and LUMO orbitals, and reactivity indices. While no significant correlations were found employing molecular parameters such as heat of formation, dipole moment, molecular polarizability, and so on, good correlations were obtained using the reactivity indices of HOMO and LUMO orbitals at specific atoms of the molecules. These results indicate that the spatial distribution of HOMO and LUMO orbitals over these specific atoms play an important role for an increase of biological activity.

Conformational evaluation and detailed 1H and 13C NMR assignments of flavoxate, a urinary tract antispasmodic agent.

1H and 13C NMR chemical shift assignments for the urinary tract antispasmodic flavoxate (1) and flavoxate hydrochloride (2) were obtained from one- and two-dimensional measurements. A Monte Carlo random search using molecular mechanics, followed by geometry optimization of each minimum energy structure employing DFT calculations at the B3LYP/6-31G* level, and a Boltzmann analysis of the total energies, provided accurate molecular models which describe the conformational behavior of flavoxate (1). The electron density surfaces for the global minimum and the second minimum conformers 1a and 1b of this L-type Ca2+ channel inhibitor were calculated. The presence of both conformers in solution was demonstrated in full agreement with 2D NOESY data and NOE difference spectroscopy.