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

10. Patented Literature 2616 10.1. Esterification 2616 10.2. Ether Formation 2619 10.2.1. Etherification without Cyclization 2619 10.2.2. Etherification with Cyclization 2624 10.3. N-Alkylation 2625 10.4. Other Reactions 2627 11. Summary and Outlook 2628 12. Note Added in Proof 2628 13. Abbreviations Used in This Review 2629 14. Acknowledgments 2629 15. Supporting Information Available 2630 16. References 2630

Mitsunobu and Related Reactions: Advances and Applications

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.

Natural product drug discovery in the next millennium.

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.

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

The human immunodeficiency virus (HIV) has now been established as the causative agent of the acquired immunodeficiency syndrome (AIDS) for over 20 years. During this time an unprecedented success has been achieved in discovering anti-HIV drugs as reflected by the fact that there are now more drugs approved for the treatment of HIV than for all other viral infections taken together. The currently Food and DrugAdministration (FDA) approved anti-HIVdrugs can be divided into seven groups: nucleoside reverse transcriptase inhibitors (NRTIs), nucleotide reverse transcriptase inhibitors (NtRTIs), non-nucleoside reverse transcriptase inhibitors (NNRTIs), protease inhibitors (PIs), fusion inhibitors (FIs), co-receptor inhibitors (CRIs), and integrase inhibitors (INIs). This arsenal of drugs, which is used in combinations, has moved the prognosis of HIV patients from that of high morbidity and mortality to, for many at least, a chronic, manageable but still complex disease. However, the use of these drugs has been relatively limited by their toxicity, drug resistance development, and more worryingly, the fact that some newly HIV-infected patients carry viruses that are already resistant to the currently approvedAIDS treatments. These issues along with drug-related side effects as well as, in some cases, poor tolerability of these drugs make it apparent that new anti-HIV drugs with acceptable toxicity and resistance profiles and, more importantly, new anti-HIV agents with novel mechanisms of action are clearly needed.

Twenty-Six Years of Anti-HIV Drug Discovery: Where Do We Stand and Where Do We Go?

A method of preparing (±)-calanolide A, 1, a potent HIV reverse transcriptase inhibitor, from chromene 4 is provided. Useful intermediates for preparing (+)-calanolide A and its derivatives are also provided. According to the disclosed method, chromene 4 intermediate was reacted with acetaldehyde diethyl acetal or paraldehyde in the presence of an acid catalyst with heating, or a two-step reaction including an aldol reaction with acetaldehyde and cyclization either under acidic conditions or neutral Mitsunobu conditions, to produce chromanone 7. Reduction of chromanone 7 with sodium borohydride, in the presence of cerium trichloride, produced (±)-calanolide A. A method for resolving (±)-calanolide A into its optically active forms by a chiral HPLC system or by enzymatic acylation and hydrolysis is also disclosed. Finally, a method for treating or preventing viral infections using (±)-calanolide A or (-)-calanolide A is provided.

Method for the preparation of aldol product 7B

A method of preparing (±)-calanolide A, 1 , a potent
HIV reverse transcriptase inhibitor, from chromene 4 is
provided. Useful intermediates for preparing (±)-calanolide
A and its derivatives are also provided.
According to the disclosed method, chromene 4 intermediate
was reacted with acetaldehyde diethyl acetal or
paraldehyde in the presence of an acid catalyst with
heating, or a two-step reaction including an aldol
reaction with acetaldehyde and cyclization either under
acidic conditions or neutral Mitsunobu conditions, to
produce chromanone 7 . Reduction of chromanone 7 with
sodium borohydride, in the presence of cerium trichloride,
produced (±)-calanolide A. A method for resolving (±)-calanolide
A into its optically active forms by a chiral
HPLC system or by enzymatic acylation and hydrolysis is
also disclosed. Finally, a method for treating or
preventing viral infections using (±)-calanolide or (-)-calanolide
is provided.

John D. Rizzo

Papers

Method for the preparation of aldol product 7B

Method for the preparation of (+/-)-calanolide A

Method for the preparation of (+/-)-calanolide A and intermediates there of

Method for the preparation of chromanone derivatives

A Versatile Approach for Synthesis of 2,3-Dimethyl Chroman-4-ones, Intermediates for Calanolide Anti-HIV Agents, via Aldol/Mitsunobu Reactions.