Emmanuel N. Pitsinos

Inhibition of topoisomerase I by naphthoquinone derivatives

Alkannin and shikonin are naturally occurring naphthoquinones. We have tested several derivatives of the title compounds and we have found that naphthoquinones bearing at least one phenolic hydroxyl group are potent inhibitors of topoisomerase I. The ability of the tested compounds to complex Zn++ parallels with a few exceptions their topoisomerase I inhibition properties while their intercalation and redox properties do not.

Biomimetic Explorations Towards the Bisorbicillinoids: Total Synthesis of Bisorbicillinol, Bisorbibutenolide, and Trichodimerol**

Strikingly simple cascade dimerization sequences can be used to assemble the complex frameworks of bisorbicillinoids such as bisorbicillinol (1), bisorbibutenolide (2), and trichodimerol (3). The mechanistic facets of the biomimetic total syntheses of these bioactive natural products were also explored. Inspection of the unique molecular architecture of these compounds reveals that they are likely to be assembled in nature by a dimerization of two oxidized forms of sorbicillin.

Synthetic calicheamicin mimics with novel initiation mechanisms: DNA cleavage, cytotoxicity, and apoptosis.

BACKGROUND Calicheamicin gamma 1I is a bacterial product that is a prominent member of the enediyne class of antitumor antibiotics, and has been extensively studied. Calicheamicin gamma 1I binds to DNA, causing double-stranded breaks, and cells exposed to it eventually become apoptotic. It can now be made synthetically, and highly potent biological mimics have been designed. Such molecules have many potential clinical applications, but are complex to make. We therefore investigated whether simplified versions of these molecules are biologically active. RESULTS We designed and synthesized a number of simple calicheamicin mimics and evaluated their biological activity. We also constructed mimics that are particularly suitable for conjugation to proteins, oligonucleotides, and other delivery systems. Several active mimics were found, and two in particular, which lack the trisulfide and oligosaccharide moieties of calicheamicin, had potent DNA-cleaving and cytotoxic activities. They caused chiefly single-stranded cuts in DNA, however, unlike the natural molecule, which causes double-stranded DNA cuts. Although they were able to induce apoptosis, they were less potent than the natural compound in this assay. CONCLUSIONS The simple enediyne mimics were less potent than calicheamicin gamma 1I, presumably because they lack the oligosaccharide DNA-binding domain. Nevertheless, considering their relatively primitive structures, they have remarkable biological properties. They may be useful biological tools and are potential leads for the development of chemotherapeutic agents. We propose that the ability of the enediynes to induce apoptosis is related to their ability to make double-stranded cuts in DNA.

Synthesis and Evaluation of Three Novel Scyphostatin Analogues as Neutral Sphingomyelinase Inhibitors

Low-molecular-weightinhibit ors of sphingomyelinases have attracted considerable attention as molecular tools for the investigation of the enzymatic mechanism of the various isoforms of these enzymes and for clarification of their biological role, as well as the role of the product of their action on sphingomyelin (ceramide), in apoptosis and signal-transduction processes. In addition, such molecules might prove valuable for the development of new therapies for various inflammatory and autoimmune diseases. [1]

Biomimetische Studien zu den Bisorbicillinoiden: Totalsynthese von Bisorbicillinol, Bisorbibutenolid und Trichodimerol

Durch verbluffend einfache Kaskaden-Dimerisierungen konnen die komplexen Geruste von Bisorbicillinoiden wie Bisorbicillinol 1, Bisorbibutenolid 2 und Trichodimerol 3 aufgebaut werden. Bei der biomimetischen Totalsynthese dieser bioaktiven Naturstoffe wurden auch mechanistische Aspekte untersucht. Eine Analyse des einzigartigen Molekulaufbaus dieser Verbindungen ergab, das sie in der Natur wahrscheinlich durch Dimerisierung von zwei Molekulen einer oxidierten Form von Sorbicillin gebildet werden.

Streamlined Total Synthesis of Uncialamycin and Its Application to the Synthesis of Designed Analogues for Biological Investigations

From the enediyne class of antitumor antibiotics, uncialamycin is among the rarest and most potent, yet one of the structurally simpler, making it attractive for chemical synthesis and potential applications in biology and medicine. In this article we describe a streamlined and practical enantioselective total synthesis of uncialamycin that is amenable to the synthesis of novel analogues and renders the natural product readily available for biological and drug development studies. Starting from hydroxy- or methoxyisatin, the synthesis features a Noyori enantioselective reduction, a Yamaguchi acetylide-pyridinium coupling, a stereoselective acetylide-aldehyde cyclization, and a newly developed annulation reaction that allows efficient coupling of a cyanophthalide and a p-methoxy semiquinone aminal to forge the anthraquinone moiety of the molecule. Overall, the developed streamlined synthesis proceeds in 22 linear steps (14 chromatographic separations) and 11% overall yield. The developed synthetic strategies and technologies were applied to the synthesis of a series of designed uncialamycin analogues equipped with suitable functional groups for conjugation to antibodies and other delivery systems. Biological evaluation of a select number of these analogues led to the identification of compounds with low picomolar potencies against certain cancer cell lines. These compounds and others like them may serve as powerful payloads for the development of antibody drug conjugates (ADCs) intended for personalized targeted cancer therapy.

Influence of the scyphostatin side chain on the mode of inhibition of neutral sphingomyelinase

Sphingomyelin is a ubiquitous constituent of cell membranes. Its role is not merely structural ; hydrolysis of sphingomyelin by sphingomyelinases (SMases) to generate phosphorylcholine and ceramide is the initial step in the so-called sphingomyelin signal transduction pathway. In this respect, two of the many different forms of SMase identified to date have been the focus of intensive research: the acidic sphingomyelinase (ASMase), primarily found in the lysosomes, and the Mg-dependent, membrane-bound neutral sphingomyelinase (NSMase). Potent, specific inhibitors of these enzymes might not only prove to be valuable probes in deciphering their biological role but may also lead to the development of novel therapeutics for the treatment of inflammation and immunological and neurological disorders. Scyphostatin (1) was isolated from the culture broth of the cup-shaped (cup= scyphos/skufo& in ancient Greek) fungus

Synthesis and characterization of novel natural product-Gd(III) MRI contrast agent conjugates

Several novel gadolinium chelates conjugated with paclitaxel, colchicine and thyroxine have been prepared as MRI contrast agents targeted to tubulin and thyroxine-binding globulin, respectively.

A Fast Entry to Furanoditerpenoid-Based Hedgehog Signaling Inhibitors: Identifying Essential Structural Features

New, small molecule Hedgehog (Hh) pathway inhibitors, such as the furanoditerpenoid taepeenin D, are of high medicinal importance. To establish key structure-activity relationships (SARs) for this lead, a synthetic sequence has been developed for the expedient preparation of several derivatives and their evaluation as Hh inhibitors exploiting its structural similarity to abietic acid. While C(14) substitution is not essential for biological activity, the presence of a hydrogen bond acceptor at C(6) and an intact benzofuran moiety are.

Synthetic Bastadins Modify the Activity of Ryanodine Receptors in Cultured Cerebellar Granule Cells

Although the interactions of several natural bastadins with the RyR1 isoform of the ryanodine receptor in sarcoplasmic reticulum has been described, their structure-dependent interference with the RyR2 isoform, mainly expressed in cardiac muscle and brain neurons, has not been studied. In this work, we examined calcium transients induced by natural bastadin 10 and several synthetic bastadins in cultured cerebellar granule cells known to contain RyR2. The fluorescent calcium indicator fluo-3 and confocal microscopy were used to evaluate changes in the intracellular Ca2+ concentration (Cai), and the involvement of ryanodine receptors was assessed using pharmacological tools. Our results demonstrate that apart from the inactive BAST218F6 (a bisdebromo analogue of bastadin 10), synthetic bastadin 5, and synthetic analogues BAST217B, BAST240 and BAST268 (at concentrations >20 µM) increased Cai in a concentration-dependent, ryanodine- and FK-506-sensitive way, with a potency significantly exceeding that of 20 mM caffeine. Moreover, the same active bastadins at a concentration of 5 µM in the presence of ryanodine prevented a thapsigargin-induced increase in Cai. These results indicate that bastadins, acting in a structure-dependent manner, modify the activity of RyR2 in primary neuronal culture and provide new information about structure-related pharmacological properties of bastadins.