番荔枝总内酯平衡溶解度和油水分配系数的测定

目的:测定番荔枝总内酯的平衡溶解度以及表观油水分配系数,为体内吸收和设计其新剂型提供参考。方法:采用饱和法和超声振荡法分别测定番荔枝总内酯在不同溶剂中的平衡溶解度以及在正辛醇-水/缓冲溶液中的表观油水分配系数,采用比色法测定番荔枝总内酯的含量。结果:番荔枝总内酯在水和石油醚中的溶解度分别为0.06g·L-1和1.27g·L-1,其在乙醚中的溶解度最高,为482.28g·L-1;超声振荡80min后P值达到平衡,25℃下番荔枝总内酯的表观正辛醇/水分配系数P为54.91(logP=1.74),在pH 6.8的缓冲溶液中的表观分配系数最大为32.03(logP=1.51)。结论:番荔枝总内酯易溶于常用的有机溶剂,在中等极性溶剂的溶解度较大;平衡方法、平衡时间及pH对油水分配系数都有一定的影响。     

去氢骆驼蓬碱衍生物H-Y-B在不同介质中平衡溶解度、表观油水分配系数及解离常数的测定

目的 测定去氢骆驼蓬碱衍生物H-Y-B在不同pH缓冲液及不同溶剂中的平衡溶解度、正辛醇-水/缓冲溶液体系中的表观油水分配系数(lgP)及其解离常数(pKa),为H-Y-B的剂型设计提供依据。方法 采用HPLC法测定H-Y-B的浓度，以饱和溶液法测定H-Y-B在不同pH缓冲液及不同溶剂中的平衡溶解度；以正辛醇-水/缓冲溶液为模拟系统，采用摇瓶法-HPLC法测定H-Y-B的表观油水分配系数；使用紫外分光光度法测定H-Y-B的解离常数。结果 在37℃下，H-Y-B在pH为10.3中的溶解度最高，为(418.62±1.68)mg·mL^-1,在pH为1.83中的溶解度最低，为(189.21±1.58)mg·mL^-1。H-Y-B在水中的溶解度为(305.82±2.43)mg·mL^-1,在有机溶剂中的溶解度顺序为甲醇>二甲基亚砜>乙醇>异丙醇>正辛醇>乙腈>丙酮>乙酸乙酯；H-Y-B在水中lgP为0.63,在pH 6.8缓冲液中的lgP为0.50;H-Y-B的pKa值为(6.42±0.52)。...     

pH值对盐酸小檗碱表观油水分配系数的影响

目的测定盐酸小檗碱在正辛醇-水和正辛醇-缓冲液体系中的表观油水分配系数,为其体内吸收研究提供参考。方法采用HPLC法测定盐酸小檗碱的浓度,采用经典摇瓶法测定盐酸小檗碱在正辛醇-水/缓冲液中的表观油水分配系数。结果在37.0℃时,盐酸小檗碱在水中的表观油水分配系数为0.084(lgPapp=-1.08);在pH值为1.0、2.0、11.0、12.0的缓冲液中,其油水分配系数分别为1.74、1.22、1.91、15.17;在pH值为3.0～10.0时,其油水分配系数极小,变化不大,lgPapp均<0。结论在水及pH值1.0～8.0的缓冲液中,盐酸小檗碱的lgPapp均<1.0,预测其在机体胃肠道并不易被吸收。pH值对盐酸小檗碱的表观油水分配系数有一定影响,在一定范围内,pH增加可使其分配系数增大,在pH 12.0的磷酸盐缓冲液中达到最大(Papp=15.17,lgPapp=1.18)。     

高效液相色谱法测定去氧氟尿苷在不同介质中的平衡溶解度和表观油水分配系数

目的测定去氧氟尿苷在不同介质中的平衡溶解度以及在正辛醇-水和正辛醇-缓冲液体系中的表观油水分配系数。方法采用HPLC法测定去氧氟尿苷的浓度,采用摇瓶法测定去氧氟尿苷的表观油水分配系数。结果37℃,pH=7时去氧氟尿苷在水中的平衡溶解度为2.570 1 g.L-1,在pH〈5磷酸盐缓冲液中的平衡溶解度较低;去氧氟尿苷在正辛醇和水相中表观油水分配系数Papp为0.97;当pH〈7时,受pH影响不显著,表现为亲水性。结论去氧氟尿苷在水中的平衡溶解度及油水分配系数与介质的pH值有关,可以通过改变pH值,增加该药物新剂型的稳定性。     

非布索坦平衡溶解度、表观油水分配系数及解离常数的测定

目的:测定非布索坦的平衡溶解度、表观油水分配系数及解离常数。方法:采用超高效液相色谱法测定非布索坦在37℃下不同pH值缓冲液中的平衡溶解度及表观油水分配系数,并分别通过平衡溶解度法及紫外吸光度法测定其解离常数。结果:非布索坦的平衡溶解度随缓冲液的pH值升高而增大,而表观油水分配系数则相应减小,当pH为7.0时,平衡溶解度为246.4 mg.L-1,表观油水分配系数为15.49;平衡溶解度法与紫外吸光度法测得的非布索坦的解离常数十分接近,分别为4.08与4.07。结论:非布索坦的溶解度较小,在酸性条件下几乎不溶,中性条件下极微溶解,碱性条件下微溶,不适合制备静注制剂,但由于其油水分配系数较高,具有较强的跨膜能力,可采用口服途径给药。     

补骨脂酚平衡溶解度和表观油水分配系数的测定

目的 测定补骨脂酚的平衡溶解度及其在正辛醇-水/缓冲液体系中的表观油水分配系数,为补骨脂酚的剂型设计提供依据.方法 采用HPLC测定补骨脂酚在不同pH介质中的平衡溶解度及其在正辛醇-水/缓冲液体系中的表观油水分配系数P.结果 37℃时补骨脂酚在水中的平衡溶解度为0.86 ±0.19 mg·L-1,pH7.4缓冲液中平衡溶解度为1.35±0.30 mg·L-1.37℃时补骨脂酚的logP为4.27 ±0.08.结论 补骨脂酚为溶解度小的亲脂性药物,不同pH下P变化不大.     

HPLC法测定洋川芎内酯Ⅰ的平衡溶解度和表观油水分配系数

目的:测定洋川芎内酯Ⅰ的平衡溶解度和油水分配系数,为设计洋川芎内酯Ⅰ新剂型提供基础。方法:采用HPLC法测定洋川芎内酯Ⅰ的浓度,使用Megres-C18色谱柱(5μm,4.6 mm×100 mm),以乙腈-水(1∶3,v/v)为流动相,流速为1.0 mL.min-1,检测波长278 nm,测定洋川芎内酯Ⅰ在水和不同pH缓冲液介质中的平衡溶解度,及其在正辛醇-水/缓冲液中的表观油水分配系数。结果:37℃下洋川芎内酯Ⅰ在水中的平衡溶解度为34.31 mg.mL-1;洋川芎内酯Ⅰ在pH≥9.0的缓冲液溶剂体系中不稳定。在正辛醇-水体系中的表观油水分配系数13.43(lgPapp=1.13);pH值对洋川芎内酯Ⅰ表观油水分配系数影响不大。结论:洋川芎内酯Ⅰ水溶性好,表观油水分配系数适中,相对分子质量较小,可借此解析其快速入血入脑过程,预测洋川芎内酯Ⅰ有较好的应用价值。     

川芎嗪平衡溶解度及油/水分配系数的研究

目的测定川芎嗪在不同pH值下的平衡溶解度和油水分配系数(P)。方法采用摇瓶法测定表观溶解度,通过药物分配平衡后在油相和水相中的浓度比,计算油水分配系数。结果川芎嗪在二氯甲烷、乙腈、乙酸乙酯等有机溶剂中溶解度较大,在聚乙二醇400中不溶。在蒸馏水中几乎不溶,随着pH值增大,川芎嗪的溶解度变小;川芎嗪正辛醇溶液质量浓度对川芎嗪油水分配系数无明显影响,pH值对川芎嗪油水分配系数有影响,随pH值增大川芎嗪油水分配系数增大。结论药物在水中的平衡溶解度及油水分配系数与介质的pH值有关,当pH>7.24时,川芎嗪的溶解度陡然下降;当pH>6.8时,药物在油相中分配较多,川芎嗪在正辛醇-水体系中的油水分配系数P=12.33。     

pH值对瑞格列奈平衡溶解度及油水分配系数的影响

目的 测定瑞格列奈在不同pH溶液中的平衡溶解度及其在正辛醇-水系统中的油水分配系数,为瑞格列奈动力学性质、新剂型设计和生物药剂学分类提供依据.方法 采用摇瓶-高效液相色谱法分别测定瑞格列奈在不同pH溶液中的平衡溶解度和正辛醇-水/缓冲液体系中的油水分配系数.结果 在37℃下,瑞格列奈在pH为1.0、2.0、3.0、4....     

熊果酸平衡溶解度和油水分配系数的测定

目的测定熊果酸的平衡溶解度及其在正辛醇-水中的表观油水分配系数,为设计熊果酸新剂型提供基础。方法采用HPLC测定熊果酸在不同pH介质、不同溶剂中的溶解度及熊果酸在正辛醇-水中的表观油水分配系数。结果 25℃下熊果酸在水中的平衡溶解度为5.64 mg.L 1,在pH 2.0~7.4的缓冲体系中,熊果酸的溶解度不受pH的影响。熊果酸在油中溶解度不佳,在表面活性剂及半极性溶剂中溶解度相对较好,在正辛醇-水体系中的油水分配系数1gP=2.17。结论熊果酸为溶解度小的亲脂性药物。     

CARBON-13 N.M.R. STUDY OF BLEOMYCIN-A2 PROTONATION

The acid-base titration of bleomycin-A₂ in D₂O solution at 35 ± 5° has been monitored by ¹³C n.m.r. spectroscopy at 67.89 MHz. The following pK^D_a values were obtained: 3.68 ± 0.05 (secondary amine), 5.29 ± 0.03 (imidazole), and 8.23 ± 0.19 (primary amine), where K^D_a is the dissociation constant in D₂O solution. The equilibrium isotope effects (pK^D_a -pK_a in H₂O) are: 0.70 ± 0.06 (secondary amine), 0.28 ± 0.04 (imidazole), and 0.85 ± 0.19 (primary amine). Titration of the imidazole group of Bleo-A₂ occurs at N^π, i.e. only N^π is protonated in basic solution. Significant protonation shifts are almost completely limited to carbons of the N-terminal tetrapeptide, suggesting that the C-terminal tripeptide extends into the solvent and interacts to a minimal extent with the rest of the molecule. Long range protonation shifts associated with titration of the imidazole and secondary amine groups indicate that protonation of one or both of these sites is probably accompanied by significant conformational changes. The observed protonation shifts generally fail to correlate with Zn(II) complexation shifts reported by Dabrowiak et al. (1973, Biochemistry 17, 4090) indicating that ligation sites cannot unambiguously be determined from these complexation shifts. The complexation shifts previously attributed to coordination of the imidazole and carbamoyl groups probably result from conformational changes.     

Equilibrium and Kinetics of Rotamer Interconversion in Immunosuppressant Prodigiosin Derivatives in Solution

The equilibrium and relative rate of rotamer interconversion around the bond joining the 2,2′‐bipyrrolyl and pyrromethene moieties in a synthetic analogue of immunosuppressant prodigiosin are investigated as a function of pHapp in a water/acetonitrile mixture (1/1 by volume). Two chromatographically separable isomeric forms are obtained in acid solutions (pHapp < 4), whereas rapid intercon‐version occurs above neutrality. Furthermore, pH modulates the conformational preference of the molecule according to nitrogen protonation on the three pyrrole rings system (pK_a = 7.2). At high pHapp (neutral form), the same conformer that is observed in pure acetonitrile prevails, whereas the other one is preferred by the protonated form. The nuclear magnetic resonance data indicate that the structures of the two conformers mainly differ in the value of the torsion angle around the aforementioned C–C bond. Kinetic and equilibrium data are quantitatively interpreted with a cyclic mechanism including two protonation (pK_a1 = 8.23 ± 0.03, pK_a2 = 5.4 ± 0.2) and two conformational rearrangement steps. A molecular interpretation of the observed behavior includes, for the preferred conformer at low pH, formation of a new hydrogen bond between the exocyclic oxygen and the neighboring pyrrole NH upon protonation of the three pyrrole rings system.     

Activation of recombinant h 5-HT1B and h 5-HT1D receptors stably expressed in C6 glioma cells produces increases in Ca2+-dependent K+ current

The putative coupling between stably expressed recombinant h 5-HT_1B or h 5-HT_1D receptors and K⁺ channels which regulate excitability was investigated in C6 glioma cells. Outward K⁺ currents (I _K) were examined in non-transfected C6 glioma cells and in cells expressing cloned h 5-HT_1B or h 5-HT_1D receptors using the patch-clamp technique in the whole-cell configuration. I _K was elicited by a depolarizing step from a holding potential of –60 mV. In C6 glioma cells expressing either recombinant h 5-HT_1B or h 5-HT_1D receptors, sumatriptan similarly increased I _K in a concentration-dependent manner (maximum increase 19.4±7.2%, n=8, P<0.05 and 25.1±3.9%, n=6, P<0.001, respectively) with EC₅₀ values (geometric mean with 95% confidence intervals in parentheses) of 56.3 nM (7.9–140 nM) and 68.7 nM (16–120 nM), respectively. Sumatriptan failed to elicit increases in I _K in non-transfected cells, confirming a specific involvement of the respective membrane h 5-HT_1B and h 5-HT_1D receptors in transfected C6 cells. In the presence of the mixed 5-HT_1B/D receptor antagonist GR 127935 (0.1 μM), sumatriptan (1 μM) failed to significantly increase I _K in C6 cells expressing h 5-HT_1B receptors (–7.5±3.5%, P=NS, n=6), although a higher concentration of GR 127935 (1 μM) was required to significantly inhibit sumatriptan-evoked increases in I _K in C6 cells expressing h 5-HT_1D receptors (–1.8±3.5%, P=NS, n=6), confirming that sumatriptan-evoked responses were indeed mediated by h 5-HT_1B and h 5-HT_1D receptors, respectively. In C6 cells expressing either cloned h 5-HT_1B or h 5-HT_1D receptors, sumatriptan-induced increases in I _K were prevented by the calcium chelator EGTA (5 mM) when included in the patch pipette (maximum increase 0.57±0.6%, n=3, P=NS and –2.8±1.6%, n=5, P=NS, respectively). In C6 cells expressing cloned h 5-HT_1B receptors, sumatriptan (1 μM) similarly failed to significantly increase I _K in the presence of dibutyryl cAMP (10 μM) or when a nominally Ca²⁺-free medium was included in the patch pipette (–19.4±5.1%, n=5 and –5.2±4.3%, n=5, respectively, P=NS in each case). In addition, the Ca²⁺-dependent K⁺ channel blockers iberiotoxin (0.1 μM) and tetraethylammonium (TEA, 1 mM) abolished sumatriptan-induced increases in I _K (–0.5±1.0%, n=4 and –3.9±3.1%, n=4, respectively, P=NS in each case) in C6 cells expressing h 5-HT_1B receptors, confirming the involvement of Ca²⁺-dependent K⁺ channels. In C6 cells expressing cloned h 5-HT_1B receptors, sumatriptan (1 μM) similarly failed to significantly increase I _k after 30-min incubation with thapsigargin (1 μM) or when heparin (2 mg/ml) was included in the patch pipette (1.1±0.4%, n=5 and 1.2±2.4%, n=5, respectively, P=NS). In conclusion, evidence is provided that both recombinant h 5-HT_1B and h 5-HT_1D receptors stably transfected in C6 glioma cells are positively coupled to Ca²⁺-dependent K⁺ channels, and the outward hyperpolarizing current mediated by these channels is dependent upon IP₃ receptor-mediated intracellular Ca²⁺ release. Received: 15 April 1998 / Accepted: 9 September 1998     

Bilayer Composition,Temperature, Speciation Effects and the Role of Bilayer Chain Ordering on Partitioning of Dexamethasone and its 21-Phosphate

Purpose

Models to predict membrane-water partition coefficients (K_p) as a function of drug structure, membrane composition, and solution properties would be useful. This study explores the partitioning of dexamethasone (Dex) and its ionizable 21-phosphate (Dex-P) in liposomes varying in acyl chain length, physical state, and pH.

Methods

DMPC:mPEG DMPE, DPPC:mPEG DPPE, and DSPC:mPEG DSPE (95:5 mol%) liposomes were prepared by thin film hydration. K_p values for Dex and Dex-P were determined from pH 1.5–8 by equilibrium dialysis and equilibrium solubility (Dex).

Results

Dex K_p values at 25°C were 705?±?24, 106?±?11, and 58?±?9 in DMPC, DPPC, and DSPC, increasing to 478?±?20 in DPPC liposomes at 45°C. Both neutral and anionic species contributed to the K_p of Dex-P versus solution pH (1.5–8). A linear correlation was found between the natural logarithm of K_p and the inverse of bilayer free surface area (1/a_free) where a_free is a parameter reflecting chain ordering that depends on bilayer composition and temperature.

Conclusions

Models of the pH dependence of partitioning of ionizable compounds must include contributions of both neutral and ionized species. Bilayer free surface area may be an important variable to predict K_p of drug molecules versus lipid composition and temperature.

     

Comparative Studies on the N-Oxidation of Aniline and N,N-Dimethylaniline by Rabbit Liver Microsomes

1. Rate studies of N-oxidation of aniline and N,N-dimethylaniline by rabbit liver microsomal preparations were performed at different pH values. The apparent pKs of the free functional groups were 7.2 and 6.9, respectively, at 26°. The apparent heats of ionization of these groups varied from 26.8 to 31.8 kJ mol^?1.

2. Photo-oxidation of the microsomal mixed function oxidase resulted in rapid loss of N-oxygenating activity. The enzyme was markedly protected from inactivation by the presence of aniline or N,N-dimethylaniline. The apparent K_D values for protection were close to the K_m and K_s values for the individual arylamines. The pH profiles of the initial rates of photo-inactivation resembled the titration curves of groups with an apparent pK_a between 6.0 and 6.2.

3. The N-oxidase was strongly inhibited by diethyl pyrocarbonate at pH 6.0. Catalytic capacity was partially restored by treatment with neutral hydroxyl-amine. Pyridine protected the enzyme from acylation.

4. A close relationship exists between the N-hydroxylation of aniline and the N-oxide formation from N,N-dimethylaniline with respect to sensitivity to photo-oxidation, reactivity to protective substrates and susceptibility to carb-ethoxylation.     

CHARACTERIZATION OF BINDING SITES FOR [3H]-IDAZOXAN, [3H]-P-AMINOCLONIDINE AND [3H]-RAUWOLSCINE IN THE KIDNEY OF THE DOG

1. We characterized the binding of [³H]-rauwolscine, [³H]-p-aminoclonidine and [³H]-idazoxan in a dog kidney membrane preparation. Our aim was to determine the pharmacological nature of the α₂-adrenoceptor- and imidazoline-preferring binding sites in this organ. 2. [³H]-Rauwolscine bound to an apparent single site with an affinity (K_D) of 2.2 nmol/ L and a maximum density (B_max) of 58.5 fmol/mg protein, when 10 μmol/L idazoxan defined non-specific binding. However displacement studies demonstrated that a number of compounds, including prazosin, inhibited [³H]-rauwolscine binding in a complex manner consistent with displacement from two distinct binding sites. The majority (69%) of the [³H]-rauwolscine binding sites had a relatively low affinity for prazosin (K_I= 398 nmol/L), while the remainder had a relatively high affinity for prazosin (K_I= 7.9 nmol/ L). 3. [³H]-p-Aminoclonidine bound to an apparent single site (K_D= 5.2 nmol/L; B_max= 72.4 fmol/mg protein), when 10 μmol/L phentolamine defined non-specific binding. When 1 μmol/L of the potent and selective α₂-adrenoceptor antagonist 2-methoxyidazoxan was included in the incubate, no specific binding was detected. We therefore conclude that under the conditions of this experiment [³H]-p-aminoclonidine binds only to α₂-adrenoceptors in the dog kidney. 4. [³H]-Idazoxan bound to two sites, with a higher (K_D= 0.95 nmol/L; B_max= 43.9 fmol/mg protein) and lower (K_D= 9.1 nmol/L; B_max= 93.8 fmol/mg protein) affinity, respectively, when 1 mmol/L phentolamine defined non-specific binding. When 10 μmol/ L GTPγS was included in the incubate, the low affinity site was unaffected but the maximum binding at the higher affinity site was reduced by 79%. 2-Methoxyidazoxan displaced [³H]-idazoxan in a monophasic manner and with low potency (IG₅₀=11.5 μmol/L). Yohimbine, efaroxan, clonidine, rilmenidine, guanabenz and idazoxan itself displaced [³H]-idazoxan in a complex manner; the slope of the displacement curves being less than unity. 5. We conclude that the dog kidney contains a heterogeneous population of α₂-adrenoceptors that can be labelled either with [³H]-rauwolscine or [³H]-p-aminoclonidine. The dog kidney also contains a heterogeneous population of non-adrenoceptor imidazoline-preferring binding sites of the I₂-subtype, that can be labelled with [³H]-idazoxan. The binding site for which [³H]-idazoxan has the highest affinity appears to be coupled to a guanine nucleotide binding regulatory protein.     

Perivascular Tissue Pharmacokinetics of Dipyridamole

Purpose The tissue diffusivity (D_g) and partitioning (K) for dipyridamole were determined and a model was developed to examine the relationship between perivascular dose and local dipyridamole tissue concentrations. Methods Experiments were performed using an in vitro perfusion apparatus that recirculated buffer through different graft samples or normal porcine femoral arteries and veins. The grafts or blood vessels were immersed in a compartment containing Krebs–Henseleit (KH) buffer and dipyridamole (30 μg/mL). The recirculating buffer was sampled at multiple time points and dipyridamole was assayed. Estimates of the effective diffusivity (D_g) and partition coefficient (K) of the drug in the vessel wall were determined and used to simulate dipyridamole tissue concentration after perivascular delivery. Results Dipyridamole diffusivity within native femoral veins (D_g = 3.87 ± 0.93 × 10⁻⁶ cm²/s) was approximately twice that within femoral arteries (D_g = 2.06 ± 0.79 × 10⁻⁶ cm²/s, p < 0.01). Explanted grafts showed the lowest diffusivity. Partition coefficients of femoral arteries (K = 4.11 ± 0.99) were higher than those of femoral veins (K = 2.05 ± 0.85, p < 0.01) and explanted graft (K = 0.89 ± 0.56, p<0.01). Discussion The results demonstrate that local drug kinetics vary greatly for different types of blood vessels and grafts. The pharmacokinetic parameters and resulting computational simulations are helpful in exploring perivascular drug delivery strategies.     

Electrophysiological Effects of the Anti‐Cancer Drug Lapatinib on Cardiac Repolarization

Abstract: Lapatinib is one of several tyrosine kinase inhibitors used against solid tumour cancers such as breast and lung cancer. Although lapatinib is associated with a risk of QT prolongation, the effects of the drug on cellular cardiac electrical properties and on action potential duration (APD) have not been studied. To evaluate the potential effects of lapatinib on cardiac repolarization, we investigated its electrophysiological effects using a whole‐cell patch–clamp technique in transiently transfected HEK293 cells expressing human ether‐à‐go‐go (hERG; to examine the rapidly activating delayed rectifier K⁺ current, I_Kr), KCNQ1/KCNE1 (to examine the slowly activating delayed rectifier K⁺ current, I_Ks), KCNJ2 (to examine the inwardly rectifying K⁺ current, I_K1), or SCN5A (to examine the inward Na⁺ current, I_Na) and in rat cardiac myocytes (to examine the inward Ca²⁺ current, I_Ca). We also examined its effects on the APD at 90% (APD₉₀) in isolated rabbit Purkinje fibres. In ion channel studies, lapatinib inhibited the hERG current in a concentration‐dependent manner, with a half‐maximum inhibition concentration (IC₅₀) of 0.8 ± 0.09 μm . In contrast, at concentrations up to 3 μm , lapatinib did not significantly reduce the I_Na, I_K1 or I_Ca amplitudes; at 3 μm , it did slightly inhibit the I_Ks amplitude (by 19.4 ± 4.7%; p < 0.05). At 5 μm , lapatinib induced prolongation of APD₉₀ by 16.1% (p < 0.05). These results suggest that the APD₉₀‐prolonging effect of lapatinib on rabbit Purkinje fibres is primarily a result of inhibition of the hERG current and I_Ks, but not I_Na, I_K1 or I_Ca.     

Measuring the stratum corneum reservoir: Desorption kinetics from keratin

High keratin binding and slow desorption kinetics are assumed to be responsible for the formation of the stratum corneum (SC) reservoir. We measured equilibrium binding coefficients (K_b) and desorption rate constants (k_off) with bovine hoof/horn keratin and six solutes with similar molecular weight (180–288 Da) and varying lipophilicities [expressed as octanol–water distribution coefficient, i.e., a partition coefficient corrected for pH (log K_pH) ?0.13 to 3.8]. Two ionizable solutes within this set were tested at different pH values as degree of ionization and lipophilicity were expected to influence equilibrium binding and desorption kinetics. The unbound fraction at equilibrium varied between 18% and 93%. All solutes exhibited linear binding isotherms within the investigated concentration range. Equilibrium binding and the rate of desorption are both functions of solute lipophilicity [log K_b = 1.23 + 0.32 log K_pH; log k_off = 1/(25.75 + 8.35 K_pH^0.34)]. Our results prove that slow desorption from keratin may be a major contributor to the SC reservoir. Also, they prove that reservoir formation is relevant for lipophilic solutes independent of drug class, thus allowing new options for topical pharmacotherapy. © 2012 Wiley Periodicals, Inc. and the American Pharmacists Association J Pharm Sci 101:3718–3728, 2012     

Structure Activity Relationship of Homochiral 7-Substituted 1-Aminoindans as 5-HT1A Receptor Ligands

A series of homochiral 7-substituted 1-aminoindans was prepared by means of asymmetric reductive amination from racemic 7-substituted 1-indanones via E-imines and E-imine/ enamine mixtures, respectively, and subjected to 5-hydroxytryptamine (5-HT) receptor subtype binding studies. The ee’s of the title compounds were determined by HPLC of the corresponding Mosher’s amides and range from 96 to 99.9%. The absolute configuration was elucidated by means of correlation CD spectroscopy. On the basis of the pK_I values obtained from various test systems, structure activity relationships have been established with respect to the absolute configuration, degree of N-alkylation, and the type of 7-substituents. The tested 1-aminoindans show the highest affinity to the 5-HT_1A receptor, with decreasing magnitude for the 5-HT_2A, 5-HT_1D, and 5-HT_2C receptors. The highest affinities for the 5-HT_1A receptor were observed for the R-(–)-7-propoxy-1-(di-n-propylamino)indan hydrochloride (R-(–)-30), S,S′-(+)-7-benzylamido-1-(1-phenylethylamino)indan hydrochloride [S,S′-(+)- 19 ] and R-(–)-7-methoxy-1-(di-n-propylamino)indan hydrogenembonate (R-(–)- 29 ) with pK_I = 7.07 ± 0.19, 6.40 ± 0.09, and 6.22 ± 0.10, respectively, in comparison to 8-OH-DPAT with pK_I = 8.70 ± 0.30. Nearly all other compounds showed low affinity at all 5-HT receptors tested. The three above mentioned ligands were tested on HeLa cells (cell line HA6) expressing recombinant human 5-HT_1A receptors for their effects on forskolin-stimulated cAMP accumulation in intact cells. Both the di-n-propylamino substituent bearing R-(–)- 30 and R-(–)- 29 acted as efficacious agonists with a pEC₅₀ value of 5.89 ± 0.20 for R-(–)- 30 compared to 5-HT with a pEC₅₀ value of 8.06 ± 0.14. S,S′-(+)- 19 with the 1-phenylethylamino substituent was devoid of intrinsic activity up to the highest tested concentration (10 μM).