Lobeline and structurally simplified analogs exhibit differential agonist activity and sensitivity to antagonist blockade when compared to nicotine.

In the present study, lobeline and two structurally simplified analogs were evaluated for activity in muscarinic and nicotinic binding assays, a functional assay for nicotinic receptor activation (86Rb+ efflux from striatal synaptosomes) and an acetylcholinesterase (AChE) assay. Lobeline displaced [3H]cytisine binding to rat cortical membranes with a mean inhibition constant (KI) value of 16.0 nM, while the lobeline analogs CRM-I-13-1 and CRM-I-32-1 exhibited values of 15.0 and 5.4 microM, respectively. [3H]methylscopolamine was displaced by lobeline with a mean KI value of 37.0 microM while CRM-I-13-1 and CRM-I-32-1 exhibited values of 55.0 and 16.0 microM, respectively. While nicotine stimulated 86Rb+ efflux from striatal synaptosomes in a mecamylamine reversible manner at each concentration tested, lobeline slightly increased 86Rb+ efflux at lower concentrations and reduced efflux at higher concentrations. Further, none of the lobeline effects were reversed with mecamylamine. Although less potent, the two lobeline analogs exhibited a similar pattern of activity. These data may suggest that lobeline and structurally similar compounds bind with different subtype selectivity than nicotine, or exert their agonists effects through non-nicotinic mechanisms. All of the compounds tested were at least several hundred times less potent than physostigmine as AChE inhibitors. While some differences were apparent between the lobeline analog which contained the 2-keto-ethyl portion of lobeline and the analog which contained the phenyl 2-hydroxy-ethyl moiety, each compound was much less active than lobeline in most parameters assessed.

Streptonigrin and related compounds. 5. Synthesis and evaluation of some isoquinoline analogues.

A series of analogues of streptonigrin, in which the quinoline of ring B is replaced by isoquinoline and the substituted pyridine of ring C is replaced by phenyl, nitrophenyl, aminophenyl, or benzyl functions, have been prepared. Thus, 1-substituted isoquinoline-5,8-diones with 7-amino or 6-(alkylamino) groups were prepared. The various quinones were evaluated for antimicrobial activity against Bacillus subtilis and root-growth inhibitory activity against Lepidium sativum. The effect of specific structural changes on these activities was examined with streptonigrin for comparison. The necessity of an aminoquinone function for activity is confirmed. With regard to the antibacterial activity, the isoquinoline analogues appear to be less active compared to the quinoline derivatives. However, the higher degree of antibacterial activity of the 1-benzylisoquinolines and the 1-nitrophenylisoquinolines compared to the 1-phenyl isoquinolines is noteworthy. In contrast to the results seen with the antibacterial activity, most of the isoquinoline analogues showed activity comparable to, or even higher than, that of streptonigrin in the root-growth inhibition assay. The 1-nitrophenylisoquinolines again appear to be the most active. The equal or greater potency of the benzyl analogue in comparison with the phenyl analogue was unexpected and questions the need for the extended conjugation and the geometry required for metal binding as considered earlier. It also opens up new possibilities for structural variation.

Synthesis and structure-activity relationships of 6-substituted 2',3'-dideoxypurine nucleosides as potential anti-human immunodeficiency virus agents.

In order to study the structure-activity relationships of 2',3'-dideoxypurine nucleosides as potential anti-HIV agents, various 6-substituted purine analogues have been synthesized and examined in virus-infected and uninfected human peripheral blood mononuclear cells. N6-methyl-2',3'-dideoxyadenosine (D2MeA, 7a) was initially synthesized from adenosine via 2',3'-O-bisxanthate 3. As extension of this reaction to other N6-substituted compounds failed, a total synthetic method utilizing 2',3'-dideoxyribose derivative 9 was used for the synthesis of other purine nucleosides. An acid-stable derivative of N6-methyl-2',3'-dideoxyadenosine, 2'-fluoroarabinofuranosyl analogue 32 (D2MeFA), has been synthesized from the appropriate carbohydrate 24 by condensation with N6-methyladenine 23. Among these compounds, N6-methyl derivative (D2MeA) 7a proved to be one of the most potent antiviral agents. The order of potency for the 6-substituted compounds was NHMe greater than NH2 greater than Cl approximately N(Me)2 greater than SMe greater than OH approximately NHEt greater than SH greater than NHBn approximately H. The results suggest that a bulk tolerance effect at the 6-position of the 2',3'-dideoxypurine nucleoside may dictate the antiviral activity of these compounds. Acid-stable analogue 32 (D2MeFA) was found to be 20-fold less potent than the parent compound. Both D2MeA and D2MeFA were resistant to calf intestine adenosine deaminase. The presence of a fluorine atom in the carbohydrate moiety greatly increased stability to acid, making D2MeFA a potential orally active antiviral agent that could be useful for the treatment of retroviral infections in humans.

L-beta-(2S,4S)- and L-alpha-(2S,4R)-dioxolanyl nucleosides as potential anti-HIV agents: asymmetric synthesis and structure-activity relationships.

In order to study the structure-activity relationships of L-(2S,4S)- and L-(2S,4R)-dioxolanyl nucleoside as potential anti-HIV agents, various enantiomerically pure L-(2S,4S)- and (2S,4R)-dioxolanylpyrimidine and -purine nucleosides have been synthesized and evaluated against HIV-1 in human peripheral blood mononuclear (PBM) cells. The enantiomerically pure key intermediate 8 has been synthesized in six steps from 1,6-anhydro-beta-L-gulose (2), and compound 8 was condensed with 5-substituted pyrimidines, 6-chloropurine, and 2,6-disubstituted purine to obtain various dioxolanylpyrimidine and -purine nucleosides, respectively. Among the compound synthesized, 5-fluorocytosine derivative 29 was found to exhibit the most potent anti-HIV activity (EC50 = 0.0012 microM) although it was toxic (IC50 = 10.0 microM). The order of anti-HIV potency of pyrimidine analogues was as follows: 5-fluorocytosine (beta-isomer) > cytosine (beta-isomer) > 5-fluorocytosine (alpha-isomer) > 5-iodocytosine (beta-isomer) > cytosine (alpha-isomer) > 5-bromocytosine (beta-isomer) > thymine (beta-isomer) > 5-methylcytosine (alpha-isomer) > 5-iodocytosine (alpha-isomer) > 5-chlorocytosine (beta-isomer). The anti-HIV potency of purine analogues was found to be in the following decreasing order: 2,6-diaminopurine (beta-isomer) > 2-chloroadenine (alpha-isomer) > 2-fluoroadenine (beta-isomer) > adenine (beta-isomer) > 2-amino-6-chloropurine (alpha-isomer) > 2-amino-6-chloropurine (beta-isomer) > guanine (beta-isomer) > 2-fluoroadenine (alpha-isomer) > adenine (alpha-isomer) > 2,6-diaminopurine (alpha-isomer) > N6-methyladenine (beta-isomer). It is interesting to note that the alpha-5-fluorocytosine analogue exhibited an excellent anti-HIV activity (EC50 = 0.063 microM) without cytotoxicity up to 100 microM in PBM cell.

1,3-dioxolanylpurine nucleosides (2R,4R) and (2R,4S) with selective anti-HIV-1 activity in human lymphocytes.

In order to study the structure-activity relationships of dioxolane nucleosides as potential anti-HIV-1 agents, various enantiomers of pure dioxolanylpurine nucleosides were synthesized and evaluated against HIV-1 in human peripheral blood mononuclear cells. The enantiomerically pure key intermediate 1, which was synthesized in nine steps from 1,6-anhydro-beta-D-mannose, was condensed with 6-chloropurine, 6-chloro-2-fluoropurine, and 2,6-dichloropurine in the presence of TMS triflate. The chloro or fluoro substituents were readily converted into amino, N-methylamino, hydroxy, methoxy, thiol, and methylthio under appropriate reaction conditions. Upon evaluation of these dioxolanes, the guanine derivative 24 exhibited the most potent anti-HIV-1 activity without cytotoxicity up to 100 microM in various cells. The decreasing antiviral activity order of beta-isomers was as follows: guanine > 6-chloro-2-aminopurine > 2-fluoroadenine > or = adenine > or = 2,6-diaminopurine > hypoxanthine > 2-chloroadenine > 6-chloropurine approximately equal to N6-methyladenine approximately equal to 6-mercaptopurine approximately equal to 6-(methylthio)purine.

Asymmetric synthesis of 1,3-dioxolane-pyrimidine nucleosides and their anti-HIV activity.

In order to study the structure-activity relationships of dioxolane nucleosides as potential anti-HIV agents, various enantiomerically pure dioxolane-pyrimidine nucleosides have been synthesized and evaluated against HIV-1 in human peripheral blood mononuclear cells. The enantiomerically pure key intermediate 8 has been synthesized in nine steps from 1,6-anhydro-D-mannose (1), which was condensed with 5-substituted pyrimidines to obtain various dioxolane-pyrimidine nucleosides. Upon evaluation of these compounds, cytosine derivative 19 was found to exhibit the most potent anti-HIV agent although it is the most toxic. The order of anti-HIV potency was as follows: cytosine (beta-isomer) greater than thymine greater than cytosine (alpha-isomer) greater than 5-chlorouracil greater than 5-bromouracil greater than 5-fluorouracil derivatives. Uracil, 5-methylcytosine, and 5-iodouracil derivatives were found to be inactive. Interestingly, alpha-isomer 20 showed good anti-HIV activity without cytotoxicity. As expected, other alpha-isomers did not exhibit any significant antiviral activity. (-)-Dioxolane-T was 5-fold less effective against AZT-resistant virus than AZT-sensitive virus.

Structure-activity relationships of beta-D-(2S,5R)- and alpha-D-(2S,5S)-1,3-oxathiolanyl nucleosides as potential anti-HIV agents.

The beta-D-(2S,5R)- and alpha-D-(2S,5S)-1,3-oxathiolanylpyrimidine and -purine nucleosides with natural nucleoside configuration were synthesized and evaluated against HIV-1 in human peripheral blood mononuclear (PBM) cells. The key intermediate 14, which was utilized for the synthesis of various nucleosides, was synthesized from D-mannose or D-galactose. Condensation of the acetate 14 with thymine, uracil, cytosine, and 5-substituted uracils and cytosines gave various pyrimidine nucleosides. The acetate 14 was also condensed with 6-chloropurine and 6-chloro-2-fluoropurine which were converted to various purine nucleosides. In the case of thymine, uracil, and 5-substituted uracil derivatives, most of the compounds did not exhibit any significant anti-HIV activity except 5-fluorouracil (alpha-isomer) derivative 55. Among 5-substituted cytosine analogues, 5-bromocytosine derivative (beta-isomer) 68 was found to be the most potent anti-HIV agent. In the case of purine derivatives, inosine analogue (beta-isomer) 78 was found to be the most potent anti-HIV agent in the 6-substituted purines and 2-amino-6-chloropurine derivative (beta-isomer) 90 showed the most potent activity in the 2,6-disubstituted purine series. The beta-isomers of 6-chloropurine (74), adenine (76), and N6-methyladenine (77) derivatives showed similar potencies against HIV-1, and the corresponding alpha-isomers also exhibited significant anti-HIV activity, although they were generally less potent than the beta-isomers.

Asymmetric synthesis and biological evaluation of beta-L-(2R,5S)- and alpha-L-(2R,5R)-1,3-oxathiolane-pyrimidine and -purine nucleosides as potential anti-HIV agents.

In order to study the structure-activity relationships of L-oxathiolanyl nucleosides as potential anti-HIV agents, a series of enantiomerically pure L-oxathiolanyl pyrimidine and purine nucleosides were synthesized and evaluated for anti-HIV-1 activity in human peripheral blood mononuclear (PBM) cells. The key intermediate 8 was synthesized starting from L-gulose via 1,6-thioanhydro-L-gulopyranose. The acetate 8 was condensed with thymine, 5-substituted uracils and cytosines, 6-chloropurine, and 6-chloro-2-fluoropurine to give pyrimidine and purine nucleosides. Upon evaluation of these final nucleosides, the 5-fluorocytosine derivative 51 was found to be the most potent compound among those tested. In the case of 5-substituted cytosine analogues, the antiviral potency was found to be in the following decreasing order: cytosine (beta-isomer) > 5-iodocytosine (beta-isomer) > 5-fluorocytosine (alpha-isomer) > 5-methylcytosine (alpha-isomer) > 5-methylcytosine (beta-isomer) > 5-bromocytosine (beta-isomer) > 5-chlorocytosine (beta-isomer). Among the thymine, uracil, and 5-substituted uracil derivatives, thymine (alpha-isomer) and uracil (beta-isomer) derivatives exhibited moderate anti-HIV activity. In the purine series, the antiviral potency is found to be in the following decreasing order: adenine (beta-isomer) > 6-chloropurine (beta-isomer) > 6-chloropurine (alpha-isomer) > 2-NH2-6-Cl-purine (beta-isomer) > guanine (beta-isomer) > N6-methyladenine (alpha-isomer) > N6-methyladenine (beta-isomer). The cytotoxicity was also determined in human PBM cells as well as Vero cells. None of the synthesized nucleosides was toxic up to 100 microM in PBM cells.

Chemotherapeutic agents for human immunodeficiency virus infection: mechanism of action, pharmacokinetics, metabolism, and adverse reactions.

Since the mid-1980s, four new nucleoside reverse transcriptase (RT) inhibitors (zalcitabine, didanosine, stavudine, and lamivudine), two nonnucleoside RT inhibitors (nevirapine and delavirdine), and four new protease inhibitors (saquinavir, ritonavir, indinavir, and nelfinavir) have been approved by the US Food and Drug Administration for the treatment of patients with acquired immunodeficiency syndrome. The driving force behind the development of these new agents has been the increasing need for more potent agents with reduced or modified toxicity profiles. The purpose of this article is to review the absorption, distribution, metabolism, elimination, toxicities, adverse reactions, and mechanism of action of the currently available drugs.

Inhibition of brain choline uptake by isoarecolone and lobeline derivatives: implications for potential vector-mediated brain drug delivery.

Delivery of certain compounds to brain is restricted by the nature of the blood-brain barrier (BBB). Many valuable pharmaceuticals are excluded from the CNS due to hydrophilicity or charge. These limitations have been overcome by numerous methods. One method we use is to take advantage of saturable nutrient transporters located at the barrier. These systems transport hydrophilic and charged nutrients into brain such as choline, a quaternized neurotransmitter precursor. Using knowledge of their substrate specificity, it is possible to deliver agents into brain using these nutrient carriers. In this report, derivatives of lobeline and isoarecolone were evaluated to determine if they may gain access to brain by the blood-brain barrier basic amine transporter using the in situ brain perfusion technique. These compounds do bind the blood-brain barrier basic amine transporter and may enter brain by this transport system.

Solubility of (+/-)-ibuprofen and S (+)-ibuprofen in the presence of cosolvents and cyclodextrins.

Aqueous solubility is an important parameter for the development of liquid formulations and in the determination of bioavailability of oral dosage forms. Ibuprofen (IB), a nonsteroidal anti-inflammatory drug, is a chiral molecule and is currently used clinically as a racemate (racIB). However, the S form of ibuprofen or S(+)-ibuprofen (SIB) is the biologically active isomer and is primarily responsible for the antiinflammatory activity. Phase solubility studies were carried out to compare the saturation solubilities of racIB and SIB in the presence of common pharmaceutical solvents such as glycerol, sorbitol solution, propylene glycol (PG), and polyethylene glycol (PEG 300) over the range of 20% to 80% v/v in aqueous based systems. The solubilities of the two compounds were also compared in the presence of cyclodextrins such as beta cyclodextrin (CD), hydroxypropyl beta cyclodextrin (HPCD), and beta cyclodextrin sulfobutyl ether sodium salt (CDSB) over the range of 5% to 25% w/v. Solubility determinations were carried at 25 degrees C and 37 degrees C. Cosolvents exponentially increased the solubility of both SIB and racIB, especially in the presence of PG and PEG 300. Glycerol was not very effective in increasing the aqueous solubilities of both compounds, whereas sorbitol solution had a minimal effect on their solubility. PG and PEG 300 increased the solubility of SIB by 400-fold and 1500-fold, respectively, whereas the rise in solubility for racIB was 193-fold and 700-fold, respectively, at 25 degrees C for the highest concentration of the cosolvents used (80% v/v). Of the two compounds studied, higher equilibrium solubilities were observed for SIB as compared with racIB. The derivatized cyclodextrins increased the aqueous solubility of racIB and SIB in a concentration-dependent manner giving AL type of phase diagrams. The phase solubility diagrams indicated the formation of soluble inclusion complexes between the drugs and HPCD and CDSB, which was of 1:1 stoichiometry. The addition of underivatized CD reduced the solubility of racIB and SIB via the formation of an insoluble complex. The S form formed more stable complexes with HPCD and CDSB as compared with raclB. The solubilization process is discussed in terms of solvent polarity and differential solid-state structure of raclB and SIB. The thermodynamic parameters for the solubilization process are presented.

Chiral separation of lobeline analogs using high performance capillary electrophoresis and derivatized cyclodextrins as chiral additives.

High performance capillary electrophoresis (HPCE) methods are described that will separate the enantiomers of various lobeline analogs synthesized in these laboratories. "Cyclodextrin array analysis" was used for preliminary screening and electrophoresis conditions were optimized for each investigated analog. The lobeline analogs under consideration were investigated as potential nicotinic agonists for the treatment of neurodegenerative disorders, such as Alzheimer's disease. Native alpha (alpha)-, beta (beta)-, and gamma (gamma)-cyclodextrins, methyl-beta-cyclodextrin (M-beta-CD), heptakis-(2,6-di-O-methyl)-beta-cyclodextrin (DM-beta-CD), and heptakis-(2,3,6-tri-O-methyl)-beta-cyclodextrin (TM-beta-CD), hydroxypropyl-alpha-cyclodextrin (HP-alpha-CD), hydroxypropyl-beta-cyclodextrin (HP-beta-CD) and hydroxypropl-gamma-cyclodextrin (HP-gamma-CD) were used as run buffer additives and their effect on the enantiomeric resolution of the lobeline analogs was investigated. The effect of pH, buffer concentration, voltage, temperature and organic modifier concentration on the enantiomeric resolution of the lobeline analogs was investigated. The most suitable conditions for each compound were chosen and, with detection at a wavelength of 200 nm, optimized.

Activities of the four optical isomers of 2',3'-dideoxy-3'-thiacytidine (BCH-189) against human immunodeficiency virus type 1 in human lymphocytes.

Four different isomers of 2',3'-dideoxy-3'-thiacytidine [beta-DL-(+-)-BCH-189] were evaluated in primary human lymphocytes infected with human immunodeficiency virus type 1. The beta-L-(-) isomer was the most potent enantiomer, with a median effective concentration of 1.8 nM and no discernible cytotoxicity up to 100 microM. The relative order of potencies for the isomers was beta-L-(-) greater than beta-DL-(+-) racemic greater than beta-D-(+) greater than alpha-L-(+) greater than alpha-D-(-). The beta-L-(-) enantiomer was as potent as 3'-azido-3'-deoxythymidine.

Deoxycytidine deaminase-resistant stereoisomer is the active form of (+/-)-2',3'-dideoxy-3'-thiacytidine in the inhibition of hepatitis B virus replication.

2',3'-Dideoxy-3'-thiacytidine (+/-)-SddC) was found to have potent activity against human hepatitis B virus as well as human immunodeficiency viruses in culture. The (-)form ((-)-SddC) which is resistant to deoxycytidine deaminase was found to be the more active antiviral stereoisomer than the (+)-form ((+)-SddC). The (+)-SddC is susceptible to deamination by deoxycytidine deaminase and is 25- and 12-fold more toxic than (-)-SddC in CEM cells in terms of anti-cell growth and anti-mitochondrial DNA synthesis, respectively. Similar results were obtained using a mixture of their 5-fluoro analogs ((+/-)-FSddC). Unlike 2',3'-dideoxycytidine, which is a potent inhibitor of mitochondrial DNA synthesis and results in such delayed toxicity as peripheral neuropathy with long term usage, (-)-SddC does not affect mitochondrial DNA synthesis. The (-)form is phosphorylated to (-)-SddCMP and is subsequently converted to (-)-SddCDP and (-)-SddCTP. One additional major metabolite which has been tentatively assigned the name "(-)-SddCMP sialate" was also identified. No significant difference in terms of the profiles of the metabolites was found between 4 and 24 h. There is an appreciable amount of (-)-SddCTP detectable 24 h after removal of the drug. (-)-SddCTP was also found to be approximately 3-fold more potent than (+)-SddCTP in inhibiting human hepatitis B virus DNA polymerase. This is the first nucleoside analog with the unnatural sugar configuration demonstrated to have antiviral activity.