Paul A. Keller

Convergent total synthesis of the michellamines

A convergent total synthesis of the anti-HIV michellamines (1) is described. The tetraaryl skeleton of the michellamines was constructed by formation first of the inner (nonstereogenic) biaryl axis and subsequently of the two other (stereogenic) axes in a highly convergent manner. The key transformation features a double Suzuki-type cross-coupling reaction between binaphthalene ditriflate 26 and isoquinolineboronic acid 35. Ditriflate 26 is synthesized in six steps starting from diene 6 and 2,6-dibromobenzoquinone (9) in 21% overall yield. For large scale production of 26, a substantially shortened version of an existing procedure for the preparation of bisnaphthoquinone 13 was also developed, which allows for the preparation of 13 from benzoquinone and diene 6 in five steps and 67% overall yield. Binaphthoquinone 13 was subsequently converted into ditriflate 26 in three steps and 67% overall yield. By the described synthetic strategy, michellamines A (1a) and B (1b) are produced (1a:1b = 1:2.5) in 24.6% ...

Evaluation of an ethnopharmacologically selected Bhutanese medicinal plants for their major classes of Phytochemicals and biological activities

ETHNOPHARMACOLOGICAL RELEVANCE As many as 229 medicinal plants have been currently used in the Bhutanese Traditional Medicine (BTM) as a chief ingredient of polyherbal formulations and these plants have been individually indicated for treating various types of infections including malaria, tumor, and microbial. We have focused our study only on seven species of these plants. AIM OF THE STUDY We aim to evaluate the antiplasmodial, antimicrobial, anti-Trypanosoma brucei rhodesiense and cytotoxicity activities of the seven medicinal plants of Bhutan selected using an ethno-directed bio-rational approach. This study creates a scientific basis for their use in the BTM and gives foundation for further phytochemical and biological evaluations which can result in the discovery of new drug lead compounds. MATERIALS AND METHODS A three stage process was conducted which consisted of: (1) an assessment of a pharmacopoeia and a formulary book of the BTM for their mode of plant uses; (2) selecting 25 anti-infective medicinal plants based on the five established criteria, collecting them, and screening for their major classes of phytochemicals using appropriate test protocols; and (3) finally analyzing the crude extracts of the seven medicinal plants, using the standard test protocols, for their antiplasmodial, antimicrobial, anti-Trypanosoma brucei rhodesiense and cytotoxicity activities as directed by the ethnopharmacological uses of each plant. RESULTS Out of 25 medicinal plants screened for their major classes of phytochemicals, the majority contained tannins, alkaloids and flavonoids. Out of the seven plant species investigated for their biological activities, all seven of them exhibited mild antimicrobial properties, five plants gave significant in vitro antiplasmodial activities, two plants gave moderate anti-Trypanosoma brucei rhodesiense activity, and one plant showed mild cytotoxicity. Meconopsis simplicifolia showed the highest antiplasmodial activity with IC(50) values of 0.40 μg/ml against TM4/8.2 strain (a wild type chloroquine and antifolate sensitive strain) and 6.39 μg/ml against K1CB1 (multidrug resistant strain) strain. Significantly the extracts from this plant did not show any cytotoxicity. CONCLUSIONS These findings provide the scientific basis for the use of seven medicinal plants in the BTM for the treatment of malaria, microbial infections, infectious fevers, and the Trypanosoma brucei rhodesiense infection. The results also form a good preliminary basis for the prioritization of candidate plant species for further in-depth phytochemical and pharmacological investigations toward our quest to unearth lead antiparasitic, anticancer and antimicrobial compounds.

Aryl Nitro Reduction with Iron Powder or Stannous Chloride under Ultrasonic Irradiation

Abstract The selective reduction of aryl nitro compounds in the presence of sensitive functionalities, including halide, carbonyl, nitrile, and ester substituents, under ultrasonic irradiation at 35 kHz is reported in yields of 39–98%. Iron powder proved superior to stannous chloride with high tolerance of sensitive functional groups and high yields of the desired aryl amines in relatively short reaction times. Simple experimental procedure and purification also make the iron reduction of aryl nitro compounds advantageous over other methods of reduction.

‘Biomimetic’ oxidative dimerization of korupensamine A: Completion of the first total synthesis of michellamines A, B, and C

Abstract A first synthetic access to michellamine A (1), a C2-symmetric antiviral naturally occurring quateraryl, is described, by oxidative ‘dimeriza

Chikungunya virus: emerging targets and new opportunities for medicinal chemistry.

Chikungunya virus is an emerging arbovirus that is widespread in tropical regions and is spreading quickly to temperate climates with recent epidemics in Africa and Asia and documented outbreaks in Europe and the Americas. It is having an increasingly major impact on humankind, with potentially life-threatening and debilitating arthritis. There is no treatment available, and only in the past 24 months have lead compounds for development as potential therapeutics been reported. This Perspective discusses the chikungunya virus as a significant, new emerging topic for medicinal chemistry, highlighting the key viral target proteins and their molecular functions that can be used in drug design, as well as the most important ongoing developments for anti-chikungunya virus research. It represents a complete picture of the current medicinal chemistry of chikungunya, supporting the development of chemotherapeutics through drug discovery and design targeting this virus.

Substitution, oxidation and addition reactions at C-7 of activated indoles

Abstract 4,6-Dimethoxy-2,3-diphenylindole (1) undergoes acylation, bromination, oxidative coupling and acid-catalysed addition to aldehydes at C-7 to produce a range of 7-substituted indoles (3–11), the indolo-isatin (6), the 7,7′-bi-indolyls (14), (16), (18), and the 7,7′-di-indolylmethanes (20–31). Addition to cyclopentanone gave compound (32), while Michael addition to α,β-unsaturated ketones gave compound (33) and the non-benzenoid double adduct (34). Related reactions led to the formation of the ring-fused indoles (39) and (41). Some reactions of the related indole diester (2) are also reported.

A twist of nature – the significance of atropisomers in biological systems

Recently identified natural atropisomeric compounds with potential medicinal applications are presented. The ability of natural receptors to possess differential binding between atropisomers is an important factor when considering active and inactive atropisomeric drugs, and has required the development of new techniques for atropselective synthesis of desired targets. Advances in this field therefore have significant relevance to modern pharmaceutical and medicinal chemistry. The atropisomeric natural products discussed include hibarimicinone, flavomannins, talaromannins, viriditoxin, rugulotrosin A, abyssomicin C, marinopyrroles, dixiamycins, streptorubin B, ustiloxins A-F, haouamine A, bisnicalaterines, and tedarene B, all of which show significant potential as leads in antibiotic, antiviral and anticancer studies. The importance for the development of common practices regarding atropisomer recognition and classification is also emphasized.

Corticotropin Releasing Hormone - A GPCR Drug Target

Corticotrophin Releasing Hormone (CRH) is a primary hormone in the fight or flight response targeting a membrane bound G-protein coupled receptor (GPCR). Many people worldwide stand to benefit by the development of CRH agonists and antagonists for the treatment of anxiety and depression, with additional therapeutic targets including Alzheimers, pain and the prevention of premature birth: so why the delay in development? In this review, we will discuss not only CRH, related proteins, receptors and ligands, but some of the obstacles that have arisen, as well as strategies being pursued to overcome these problems in the pursuit of this GPCR targeted therapeutic. Several key proteins influence the complex and intrinsic regulation of CRH, including its receptors (CRHR), of which 3 types have been categorised, CRHR(1), CRHR(2), CRHR(3), each containing active and inactive splice variants. Additionally, the CRH binding protein (CRHBP) is believed to moderate the effects of CRH at the receptor, whether it is as a molecular mop, or a delivery vessel, or both, is still being investigated. Homology based receptor modelling is a technique that has only recently become available with the crystallisation of bovine rhodopsin (a GPCR), [1] and the application of this technique to the CRH receptors is still in the early stages of development. Therefore, the medicinal chemist has previously had to rely on ligand-based strategies, specifically, the development of pharmacophores. Thus, an extensive number of both CRH peptide analogues and small ligands that show nanomolar antagonism have been developed with SAR libraries being integral to the iterative drug design process.

Dengue virus therapeutic intervention strategies based on viral, vector and host factors involved in disease pathogenesis

Dengue virus (DV) is the most widespread arbovirus, being endemic in over 100 countries, and is estimated to cause 50 million infections annually. Viral factors, such as the genetic composition of the virus strain can play a role in determining the virus virulence and subsequent clinical disease severity. Virus vector competence plays an integral role in virus transmission and is a critical factor in determining the severity and impact of DV outbreaks. Host genetic variations in immune-related genes, including the human leukocyte antigen, have also been shown to correlate with clinical disease and thus may play a role in regulating disease severity. The hosts immune system, however, appears to be the primary factor in DV pathogenesis with the delicate interplay of innate and acquired immunity playing a crucial role. Although current research of DV pathogenesis has been limited by the lack of an appropriate animal model, the development of DV therapeutics has been a primary focus of research groups around the world. In the past decade advances in both the development of vaccines and anti-virals have increased in dramatically. This review summarises the current understanding of viral, vector and host factors which contribute to dengue virus pathogenesis and how this knowledge is critically important in the development of pharmaceutical interventions.

Novel Pharmacophore Based Methods Reveal Gossypol as a Reverse Transcriptase Inhibitor

In a program to identify new structural entities for the inhibition of the HIV-1 reverse transcriptase (RT) enzyme via database searching, a series of RT pharmacophores were developed. By utilising a novel filtering technique, the National Cancer Institute database of compounds was scanned producing 15 compounds to be screened for activity. A notable inclusion was a series of gossypol derivatives. The testing of a series of compounds revealed the parent compound gossypol to be an HIV-1 reverse transcriptase inhibitor. These results suggest that at least a part of its anti-HIV activity is due to gossypol targeting the non-nucleoside inhibitor binding pocket of RT.