Synthesis, chromatographic resolution, and anti-human immunodeficiency virus activity of (+/-)-calanolide A and its enantiomers

Synthesis of natural product inspired compound collections

Natural products, their derivatives, and their analogues are among the most important sources for new drug candidates and tools for chemical biology and medicinal chemistry research. Therefore, there is a need for the development of efficient synthesis methods which give access to natural product derived and inspired compound collections. To meet this challenge, the requirements of multistep stereoselective syntheses, and the logic and methodology of natural product total synthesis need to be translated and adapted to the methods and formats for the synthesis of compound collections. Recent developments in the synthesis of natural product inspired compound collections having carbocyclic and heterocyclic scaffolds highlight the fact that this goal can be successfully attained. The progress made has paved the way for the integration of natural product inspired compound collections into medicinal chemistry and chemical biology research.

Chemical library and structure-activity relationships of 11-demethyl-12-oxo calanolide A analogues as anti-HIV-1 agents

(+)-Calanolide A ( 1) as a natural product was previously found as an inhibitor of HIV-1 reverse transcriptase. In our further investigation of its template, racemic 11-demethyl-12-oxo calanolide A ( 15), which had two fewer chiral carbon centers at the C-11 and C-12 positions than (+)-calanolide A, had a comparably inhibitory activity and better therapeutic index (EC 50 = 0.11 microM, TI = 818) against HIV-1 in vitro. A library based on its structural core was then designed and synthesized with introduction of nine diversity points in this article. The evaluations of anti-HIV-1 activity in vitro concluded their structure-activity relationships (SARs). A novel compound (10-bromomethyl-11-demethyl-12-oxo calanolide A, 123) was identified to have much higher inhibitory potency and therapeutic index (EC 50 = 2.85 nM, TI > 10,526) than those of the class compound against HIV-1. This finding provided a very important clue that modifications of the C ring at the C-10 position may be conducted to obtain drug candidates with better activity against HIV-1.

Chemical resolution of +/- -calanolide A, +/- -cordatolide A and their 11-demethyl analogues

The chemical resolution of (+/-)-calanolide A and (+/-)-cordatolide A into their corresponding optically active enantiomers is described. Their inhibitory activities against HIV-1 are tested in vitro.

Biologically active coumarins as inhibitors of HIV-1

Considerable progress has been made in recent years in the field of drug development against HIV. Many different kinds of natural products, including coumarins, have been found to be active in anti-HIV models and are thus undergoing further investigation. This review demonstrates the variety of coumarins with unique mechanisms of action in the different stages of HIV replication. The discovery and development of coumarins as anti-HIV agents has expanded in the past two decades. Most of the studies have been focused on the inhibitory activity of reverse transcriptase, but anti-integrase and antiprotease activities were also described. The objective of this review is to evaluate data on coumarins’ potent activity with respect to the inhibition of HIV-reverse transcriptase, HIV-integrase or HIV-protease. Recent requirements for potential anti-HIV agents increasingly require adequate definition of the mechanism of action as well as definition of toxic effects and this also applies to natural as well as synthetic coumarins. Structural modification is a powerful tool to increase the potential of bioactive principles. By applying scientific expertise and modern scientific technology, new single compounds will assuredly be developed as potent anti-HIV candidates for world-class new drug development.

Synthesis of chromanones: a novel palladium-catalyzed Wacker-type oxidative cyclization involving 1,5-hydride alkyl to palladium migration

A series of 2-methylchromanone derivatives have been prepared by using a novel palladium-catalyzed Wacker-type oxidative cyclization, in which a 1,5-hydride alkyl to palladium migration and a direct chirality transfer were involved.

HIV-1 reverse transcriptase inhibitors

Reverse transcriptase (RT) is one of the three enzymes encoded by the human immunodeficiency virus type 1 (HIV-1), the etiological agent of AIDS. Together with protease inhibitors, drugs inhibiting the RNA- and DNA-dependant DNA polymerase activity of RT are the major components of highly active antiretroviral therapy (HAART), which has dramatically reduced mortality and morbidity of people living with HIV-1/AIDS in developed countries. In this study, we focus on RT inhibitors approved by the US Food and Drugs Administration (FDA) or in phases II and III clinical trials. RT inhibitors belong to two main classes acting by distinct mechanisms. Nucleoside RT inhibitors (NRTIs) lack a 3' hydroxyl group on their ribose or ribose mimic moiety and thus act as chain terminators. Non-NRTIs bind into a hydrophobic pocket close to the polymerase active site and inhibit the chemical step of the polymerization reaction. For each class of inhibitors, we review the mechanism of action, the resistance mechanisms selected by the virus, and the side effects of the drugs. We also discuss the main perspectives for the development of new RT inhibitors.

Antiviral targets of a chromene derivative from Sargassum micracanthum in the replication of human cytomegalovirus

A chromene derivative (1) obtained from a brown alga, Sargassum micracanthum, has been proved to be a potent inhibitor of human cytomegalovirus (HCMV). In the present study, we evaluated its mode of action by various experimental assays. Time-of-addition experiments revealed that 1 was active if applied to cells before viral DNA synthesis, indicating that it inhibited early events of virus replication including virus adsorption and penetration, and a step immediately after viral internalization. Virus attachment and penetration studies suggested that one of the targets for anti-HCMV action of 1 was virus adsorption to cells and to a lesser extent, virus internalization was delayed in the presence of the compound. Pretreatment of virus particles with 1 showed that the compound exerted dose-dependent virucidal action. The chromene derivative and ganciclovir (GCV), an anti-HCMV drug, were synergistic inhibitors when used in combination. The synergistic effect could be explained by inhibition of different steps in HCMV replication cycle produced by 1 and GCV.

Pyranocoumarin, a novel anti-TB pharmacophore: Synthesis and biological evaluation against Mycobacterium tuberculosis

Pyranocoumarin compounds were identified to embody a novel and unique pharmacophore for anti-TB activity. A systematic approach was taken to investigate the structural characteristics. Focused libraries of compounds were synthesized and evaluated for their anti-TB activity in primary screening assays. Compounds shown to be active were further determined for MIC and MBC values. Three of the four bactericidal compounds (16, 17c, and 18f) were amino derivatives, with MIC values of 16 microg/mL and respective MBC values of 32, 32, and 64 microg/mL.

Structure-Activity Relationships of Synthetic Coumarins as HIV-1 Inhibitors

HIV/AIDS pandemics is a serious threat to health and development of mankind, and searching for effective anti-HIV agents remains actual. Considerable progress has been made in recent years in the field of drug development against HIV. A lot of structurally different coumarins were found to display potent anti-HIV activity. The current review demonstrates the variety of synthetic coumarins having unique mechanism of action referring to the different stages of HIV replication. Recent studies based on the account of various synthetic coumarins seem to indicate that some of them serve as potent non-nucleoside RT-inhibitors, another as inhibitors of HIV-integrase or HIV-protease. The merits of selecting potential anti-HIV agents to be used in rational combination drugs design and structure-activity relationships are discussed.The scientific community is looking actively for new drugs and combinations for treatment of HIV infection effective for first-line treatment, as well as against resistant mutants. The investigation on chemical anti-HIV agents gives hope and optimism about it. This review article describes recent progress in the discovery, structure modification, and structure-activity relationship studies of potent anti-HIV coumarin derivatives.

Natural products to drugs: natural product derived compounds in clinical trials

Natural product and natural product-derived compounds that are being evaluated in clinical trials or in registration (current 31 December 2004) have been reviewed. Natural product derived drugs launched in the United States of America, Europe and Japan since 1998 and new natural product templates discovered since 1990 are discussed.

Cytotoxic effects of mammea type coumarins from Calophyllum brasiliense

Calophyllum brasiliense (Clusiaceae) is a big tree from the Tropical Rain Forests of the American continent. The organic extracts from the leaves yielded coumarins of the mammea type: mammea A/BA, A/BB, B/BA, B/BB, C/OA, C/OB, B/BA cyclo F, B/BB cyclo F, and isomammeigin. The triterpenoids friedelin and canophyllol, as well as the biflavonoid amentoflavone, protocatechuic and shikimic acids, were also obtained. Most of the isolated compounds were tested in vitro against K562, U251, and PC3 human tumor cell lines. The coumarins were cytotoxic against the three cell lines, the highest activity was shown by mammea A/BA (IC50 = 0.04 to 0.59 microM). The mixtures of mammea A/BA + A/BB, mammea B/BA + B/BB and mammea C/OA + C/OB were also highly active (IC50 < 4.05 microM). Friedelin was cytotoxic only against PC3, and U251 lines. Inhibition of HIV-1 reverse transcriptase was also assayed in vitro; however, none of the tested compounds (250 microM) prevented the activity of this enzyme. Most of the isolated compounds were also inactive against fourteen bacterial strains; however mammea A/BA + A/BB, and mammea C/OA + C/OB inhibited the growth of Staphylococcus aureus, S. epidermidis and Bacillus subtilis.

Anti-HIV natural product (+)-calanolide A is active against both drug-susceptible and drug-resistant strains of Mycobacterium tuberculosis

Naturally occurring anti-HIV-1 agent (+)-calanolide A was found to be active against all of the strains of Mycobacterium tuberculosis tested, including those resistant to the standard antitubercular drugs. Efficacy evaluations in macrophages revealed that (+)-calanolide A significantly inhibited intracellular replication of M. tuberculosis H37Rv at concentrations below the MIC observed in vitro. Preliminary mechanistic studies indicated that (+)-calanolide A rapidly inhibits RNA and DNA synthesis followed by an inhibition of protein synthesis. Compared with known inhibitors, this scenario is more similar to effects observed with rifampin, an inhibitor of RNA synthesis. Since (+)-calanolide A was active against a rifampin-resistant strain, it is believed that these two agents may involve different targets. (+)-Calanolide A and its related pyranocoumarins are the first class of compounds identified to possess antimycobacterial and antiretroviral activities, representing a new pharmacophore for anti-TB activity.

HIV-1 Inhibitory Compounds from Calophyllum brasiliense Leaves

The hexane, acetone and methanol extracts of Calophyllum brasiliense leaves were fractionated following a three bioassay guide: high HIV-1 RT inhibition, low cytotoxicity on MT2 cells and high inhibition of HIV-1 IIIb/LAV replication. This led to the isolation of three anti HIV-1 dipyranocoumarins: calanolides A and B and soulattrolide. In contrast, other isolated compounds such as apetalic acid, isoapetalic acid, a structural isomer of isoapetalic acid, friedelin, canophyllol and amentoflavone were devoid of HIV-1 RT inhibitory activity. Calanolide C was also obtained as a natural product and showed moderate inhibitory properties.

Recent progress in the development of coumarin derivatives as potent anti-HIV agents

Numerous plant-derived compounds have been evaluated for inhibitory effects against HIV replication, and some coumarins have been found to inhibit different stages in the HIV replication cycle. This review article describes recent progress in the discovery, structure modification, and structure-activity relationship studies of potent anti-HIV coumarin derivatives. A dicamphanoyl-khellactone (DCK) analog, which was discovered and developed in our laboratory, and calanolide A are currently in preclinical studies and clinical trials, respectively.

Safety and pharmacokinetic profile of multiple escalating doses of (+)-calanolide A, a naturally occurring nonnucleoside reverse transcriptase inhibitor, in healthy HIV-negative volunteers

BACKGROUND

(+)-Calanolide A is a naturally occurring nonnucleoside reverse transciptase inhibitor (NNRTI) that exhibits enhanced activity against HIV-1 isolates with the Y181C mutation and retains activity against HIV-1 isolates with dual Y181C and K103N mutations. Previous studies have demonstrated that (+)-calanolide A has a favorable safety profile in both animal and human subjects.

METHOD

In this study, the safety and pharmacokinetics of multiple escalating doses of (+)-calanolide A were evaluated in a total of 47 healthy, HIV-seronegative individuals.

RESULTS

All adverse events seen in the study were mild to moderate in intensity and were transient. The most common adverse events seen were headache, dizziness, nausea, and taste perversion (oily aftertaste). Laboratory abnormalities were determined to be clinically insignificant or unrelated to (+)-calanolide A administration. No dose-related pattern in adverse event or laboratory abnormality incidence was apparent. In all cohorts examined, administration of (+)-calanolide A produced highly variable plasma levels and absorption profiles. No accumulation of parent compound was seen over the 5-day treatment course, with the day 5 area under the curve (AUC) being approximately one half of that seen on the first day of dosing. Steady-state trough plasma levels were determined in the two highest dose cohorts (600 mg and 800 mg bid for 5 days). Mean elimination half-life in the two highest dosing cohorts combined was 15.5 hours in men and 35.2 hours in women.

CONCLUSION

These pharmacokinetic properties, together with the benign safety profile, and unique in vitro resistance pattern warrant the continued development of this potential new antiviral agent.

Preliminary structure-antiangiogenic activity relationships of 4-senecioyloxymethyl-6,7-dimethoxycoumarin

Through a systematic modification of the novel angiogenesis inhibitor 4-senecioyloxymethyl-6,7-dimethoxycoumarin (1) we found that a 6,7-dimethoxy moiety is important for bioactivity of 1. Replacement of the lactone functionality in coumarin 1 by an amide decreased its activity. By substitution of the senecioyl chain with various cinnamoyl groups we discovered 6d, bearing a 4-methoxycinnamoyl instead of senecioyl side chain, with inhibitory activity in HUVEC tube formation assay enhanced by one order of magnitude compared to 1. We have also synthesized compound 12, an analogue of 6d, with equipotency and improved water solubility.

Coumarins and pyranocoumarins, potential novel pharmacophores for inhibition of measles virus replication

A series of coumarin and pyranocoumarin analogues were evaluated in vitro for antiviral efficacy against measles virus (MV), strain Chicago. Of the 22 compounds tested for inhibition, six were found to have selectivity indices greater than 10. These were compounds 5-hydroxy-7-propionyloxy-4-propylcoumarin (2a), 5,7-bis(tosyloxy)-4-propylcoumarin (7); 5-hydroxy-4-propyl-7-tosyloxy-coumarin (8); 6,6-dimethyl-9-propionyloxy-4-propyl-2H,6H-benzo[1,2-b:3,4-b']dipyran-2-one (9); 6,6-dimethyl-9-pivaloyloxy-4-propyl-2H,6H-benzo[1,2-b:3,4-b']dipyran-2-one (10); and 7,8-cis-10,11,12-trans-4-propyl-6,6,10,11-tetramethyl-7,8,9-trihydroxy-2H,6H,12H-benzo[1 ,2-b:3,4-b':5,6-b'']tripyran-2-one (18). Three of the active drugs were propyl coumarin analogues (2a, 7 and 8), two were dipyranone or chromeno-coumarins (9 and 10), and one was a benzotripyranone with a coumarin nucleus (18). Some appeared to be rather specific and potent inhibitors of MV with EC50 values ranging from 0.2 to 50 microg/ml and the majority of the EC50 values being less than 5 pg/ml. The compounds inhibited an additional nine strains of MV, and in virucidal tests the drugs did not physically disrupt the virion to inhibit virus replication. The inhibitory activity for one of the compounds tested (7) was somewhat dependent on virus concentration and it was still active when added to cells up to 24 h after virus exposure. When used in combination with ribavirin, compound 7 appeared not to profoundly affect the antiviral efficacy of ribavirin or its cell-associated toxicity. However, a slightly antagonistic MV-inhibitory effect was observed at the highest concentration of ribavirin used in combination with most concentrations of compound 7 tested. This and related compounds may be valuable leads in the development of a potent and selective class of MV inhibitors that could be used in future in the clinic.

Electrolytic partial fluorination of organic compounds. 55. Highly regio- and stereoselective anodic monofluorination of 2,3-dihydrochroman-4-one and chromone derivatives

Anodic monofluorination at the position alpha to the oxygen atom of the (E)-3-benzylidene-2,3-dihydrochroman-4-one derivatives was successfully carried out to provide the corresponding 2-fluorochromanones selectively. This is the first regioselective electrochemical fluorination of fused-type, oxygen-containing heterocyclic compounds. Anodic fluorination of a chromone derivative also gave a similar fluorinated chromanone stereoselectively.

Safety and pharmacokinetics of single doses of (+)-calanolide a, a novel, naturally occurring nonnucleoside reverse transcriptase inhibitor, in healthy, human immunodeficiency virus-negative human subjects

(+)-Calanolide A is a novel, naturally occurring, nonnucleoside inhibitor of human immunodeficiency virus type 1 (HIV-1) reverse transcriptase first isolated from a tropical tree (Calophyllum lanigerum) in the Malaysian rain forest. Previous studies have demonstrated that (+)-calanolide A has specific activity against the reverse transcriptase of HIV-1 and a favorable safety profile in animals. In addition, (+)-calanolide A exhibits a unique HIV-1 resistance profile in vitro. The safety and pharmacokinetics of (+)-calanolide A was examined in four successive single-dose cohorts (200, 400, 600, and 800 mg) in healthy, HIV-negative volunteers. In this initial phase I study, the toxicity of (+)-calanolide A was minimal in the 47 subjects treated. Dizziness, taste perversion, headache, eructation, and nausea were the most frequently reported adverse events. These events were not all judged to be related to study medication nor were they dose related. While 51% of subjects reported mild and transient dizziness, in many cases this appeared to be temporally related to phlebotomy. Calculation of the terminal-phase half-life (t(1/2)) was precluded by intrasubject variability in the 200-, 400-, and 600-mg dose cohorts but was approximately 20 h for the 800-mg dose group. (+)-Calanolide A was rapidly absorbed following administration, with time to maximum concentration of drug in plasma (T(max)) values occurring between 2.4 and 5.2 h postdosing depending on the dose. Plasma levels of (+)-calanolide A at all dosing levels were quite variable; however, both the mean concentration in plasma (C(max)), and the area under the plasma concentration-time curve increased proportionately in relation to the dose. Although raw plasma drug levels were higher in women than in men, when doses were normalized for body mass, the pharmacokinetic profiles were virtually identical with those observed for males. In general, levels of (+)-calanolide A in human plasma were higher than would have been predicted from animal studies, yet the safety profile remained benign. In conclusion, this study demonstrated the safety and favorable pharmacokinetic profile of single doses of (+)-calanolide A in healthy, HIV-negative individuals.

Natural product drug discovery in the next millennium

Nature has been a source of medicinal agents for thousands of years, and an impressive number of modern drugs have been isolated from natural sources, many based on their use in traditional medicine. In the past century, however, an increasing role has been played by microorganisms in the production of antibiotics and other drugs for the treatment of some serious diseases. Advances in the description of the human genome, as well as the genomes of pathogenic microbes and parasites, is permitting the determination of the structures of many proteins associated with disease processes. With the development of new molecular targets based on these proteins, there is an increasing demand for novel molecular diversity for screening. Natural products will play a crucial role in meeting this demand through the continued investigation of world's biodiversity, much of which remains unexplored. With less than 1% of the microbial world currently known, advances in procedures for microbial cultivation and the extraction of nucleic acids from environmental samples from soil and marine habitats, will provide access to a vast untapped reservoir of genetic and metabolic diversity. The same holds true for nucleic acids isolated from symbiotic and endophytic microbes associated with terrestrial and marine macroorganisms. By use of combinatorial chemical and biosynthetic technology, novel natural product leads will be optimized on the basis of their biological activities to yield effective chemotherapeutic and other bioactive agents. The investigation of these resources requires multi-disciplinary, national, and international collaboration in the discovery and development process.

Anti-HIV-1 activity of calanolides used in combination with other mechanistically diverse inhibitors of HIV-1 replication

The natural product (+)-calanolide A, a unique non-nucleoside reverse transcriptase inhibitor (NNRTI) of HIV-1 replication, is currently being evaluated in clinical trials in the USA. (+)-Calanolide A, the congeners costatolide and dihydrocostatolide, and (+)-12-oxo(+)-calanolide A, were evaluated in combination with a variety of mechanically diverse inhibitors of HIV replication to define the efficacy and cellular toxicity of potential clinical drug combinations. These assays should be useful in prioritizing the use of different combination drug strategies in a clinical setting. The calanolides exhibited synergistic antiviral interactions with other nucleoside and non-nucleoside reverse transcriptase inhibitors and protease inhibitors. Additive interactions were also observed when the calanolides were used with representative compounds from each of these classes of inhibitors. No evidence of either combination toxicity or antagonistic antiviral activity was detected with any of the tested compounds. The combination antiviral efficacy of three-drug combinations involving the calanolides, and the efficacy of two- and three-drug combinations using a (+)-calanolide A-resistant challenge virus (bearing the T139I amino acid change in the reverse transcriptase), was also evaluated in vitro. These assays suggest that the best combination of agents based on in vitro anti-HIV assay results would include the calanolides in combination with lamivudine and nelfinavir, since this was the only three-drug combination exhibiting a significant level of synergy. Combination assays with the (+)-calanolide A-resistant strain yielded identical results as seen with the wild-type virus, although the concentration of the calanolides had to be increased.

Quantification of (+)-calanolide A, a novel and naturally occurring anti-HIV agent, by high-performance liquid chromatography in plasma from rat, dog and human

A HPLC method was validated for quantification of (+)-calanolide A (1), a novel anti-HIV agent, in rat, dog and human plasma. The synthetic intermediate (+/-)-12-oxocalanolide A (2) was found to be a suitable internal standard. Compounds were extracted from plasma using a solid-phase C(18) cartridge and quantified over the assay range of 12.5 to 800 ng/ml. The method was utilized to determine (+)-calanolide A pharmacokinetics in rats, dogs and humans. This is the first report of a validated HPLC assay for determination of (+)-calanolide A concentrations in rat and dog plasma as well as human plasma obtained from clinical trials. There was no evidence of in vivo epimerization of (+)-calanolide A to its inactive epimer (+)-calanolide B (3).

Plant-derived and semi-synthetic calanolide compounds with in vitro activity against both human immunodeficiency virus type 1 and human cytomegalovirus

Plant-derived and semi-synthetic calanolide compounds with anti-human immunodeficiency virus type 1 (HIV-1) activity were tested for anti-human cytomegalovirus (HCMV) activity in both cytopathic effect inhibition and plaque reduction assays. The results indicated that the anti-HCMV activity of calanolide compounds does not correlate with their activity against HIV-1. The semi-synthetic 12-keto derivatives tended to be more active against HCMV than the corresponding 12-OH congeners, which were more active against HIV-1. It appeared that the 7,8-unsaturated double bond in the chromene ring played a certain role in maintaining activities against both HCMV and HIV-1. Saturation of the double bond increased the EC50 values against both viruses, with concomitant increase in toxicity. The calanolide compounds reported here are the first non-nucleoside analogues capable of inhibiting both HIV-1 and HCMV and, therefore, may be useful chemoprophylactic agents for HCMV in HIV-infected people or vice versa.

In vivo anti-HIV activity of (+)-calanolide A in the hollow fiber mouse model

In vivo anti-HIV efficacy of (+)-calanolide A has been evaluated in a hollow fiber mouse model. It was demonstrated that the compound was capable of suppressing virus replication in two distinct and separate physiologic compartments (i.p. and s.c.) following oral or parenteral administration on a once- or twice-daily treatment schedule. A synergistic effect was observed for the combination of (+)-calanolide A and AZT.

Anti-HIV coumarins from Calophyllum seed oil

The seeds of Calophyllum cerasiferum Vesque (Family-Clusiaceae), and Calophyllum inophyllum Linn. (Family-Clusiaceae) contain several known coumarins, among which were the potent HIV reverse transcriptase inhibitors costatolide and inophyllum P. Calophyllum cerasiferum contained (-)-calanolide B as its major coumarin constituent in significant amount and thus constitute a renewable source of this compound.

Pharmaceutical properties of related calanolide compounds with activity against human immunodeficiency virus

The present studies were undertaken to compare the relative pharmacokinetic parameters and bioavailability of two chemically related natural products which are nonnucleoside inhibitors of reverse transcriptase. Both (+)-calanolide A (Cal A; NSC 675451) and (+)-dihydrocalanolide A (DHCal A; NSC 678323) are currently under development for the treatment of HIV infections. HPLC-based analytical assays were developed for both compounds using modifications of a previously published procedure. The assays were used to compare the intravenous pharmacokinetics of the dihydro analogue relative to the parent compound, Cal A, and to determine the relative oral bioavailability of each drug in CD2F1 mice. Although the pharmacokinetic parameters of each drug were similar (Cal A, 25 mg/kg: AUC: 9.4 [microg/mL]. hr, t1/2beta: 0.25 h,, t1/2gamma: 1.8 h, clearance: 2.7 L/h/kg versus DHCal A, 25 mg/kg: AUC: 6.9 [microg/mL].hr, t1/2beta: 0.22 h,, t1/2gamma: 2.3 h, clearance: 3.6 L/h/kg), the oral bioavailability of DHCal A (F = 46. 8%) was markedly better than that obtained for Cal A (F = 13.2%). The relative ability of Cal A and DHCal A to change to their inactive epimer forms, (+)-calanolide B and (+)-dihydrocalanolide B, respectively, was also determined. While conversion of active to inactive forms of the drugs was noted to occur in vitro especially under acidic conditions, no epimer forms of either compound were noted in plasma of mice after administration of either CalA or DHCal A. Considered together with preliminary toxicology findings, the pharmacokinetic data obtained in the present series of experiments suggest that selection of the dihydro derivative of (+)-calanolide A may be a reasonable choice for further preclinical development and possible Phase I clinical evaluation.

In vitro anti-human immunodeficiency virus (HIV) activity of the chromanone derivative, 12-oxocalanolide A, a novel NNRTI

The three chromanone derivatives, (+)-, (-)-, and (+/-)-12-oxocalanolide A (2), were evaluated for in vitro antiviral activities against HIV and simian immunodeficiency virus (SIV). The compounds were determined to be inhibitors of HIV-1 reverse transcriptase (RT) and exhibited activity against a variety of viruses selected for resistance to other HIV-1 nonnucleoside RT inhibitors. They are the first reported calanolide analogues capable of inhibiting SIV.

Structural analogues of the calanolide anti-HIV agents. Modification of the trans-10,11-dimethyldihydropyran-12-ol ring (ring C)

(+)-Calanolide A is a potent inhibitor of reverse transcriptase from human immunodeficiency virus type 1 (HIV-1), which was isolated from an extract of Calophyllum lanigerum, along with seven related compounds. In order to examine the structure-activity relationships of the trans-10,11-dimethyldihydropyran-12-ol ring (designated ring C), a series of structural analogues were prepared and evaluated using a whole cell cytopathicity assay (XTT). Removal of the 10-methyl group resulted in decreased activity, with only one epimer exhibiting anti-HIV activity. Substituting the 10-methyl group with an ethyl chain maintained anti-HIV activity, with only a 4-fold reduction in potency relative to racemic calanolide A. Substitution of the 10-methyl group with an isopropyl moiety completely eliminated the anti-HIV activity. Addition of an extra methyl group at either the 10- or 11-position maintained the basic stereochemical features of the parent calanolide system while removing the chirality at the respective carbon, but resulted in decreased activity relative to calanolide A. In all the above examples, analogues containing a cis relationship between the 10- and 11-alkyl moieties were completely devoid of activity. Synthetic intermediates in which the 12-hydroxyl group was in the ketone oxidation state exhibited suppressing anti-HIV activity, with EC50 values only 5-fold less potent than that of calanolide A for both the 10,11-cis (6) and -trans (5) series. These ketones represent the first derivatives in the calanolide series to exhibit anti-HIV activity while not containing a 12-hydroxyl group. Likewise, ketone derivative 6 was the first example of a compound in the calanolide series having a cis relationship between the 10- and 11-methyl groups found to exhibit anti-HIV activity. Analogues which showed anti-HIV activity in the CEM-SS cytoprotection assay were further confirmed to be inhibitors of HIV-1 reverse transcriptase.

Specific inhibition of human immunodeficiency virus type 1 reverse transcriptase mediated by soulattrolide, a coumarin isolated from the latex of calophyllum teysmannii

Soulattrolide (1), a coumarin isolated from Calophyllum teysmannii latex, was found to be a potent inhibitor of HIV-1 reverse transcriptase (RT) with an IC50 of 0.34 microM. Inhibition was remarkably specific, with no appreciable activity being observed toward HIV-2 RT, AMV RT, RNA polymerase, or DNA polymerases alpha or beta.