Alexandros E. Koumbis

d- and l-Erythrose as sources of chiral quaternary carbon centers. Total synthesis of (−)-malyngolide and (+)-tanikolide

Abstract A highly efficient and versatile approach was applied for the total synthesis of the marine natural products (−)-malyngolide and (+)-tanikolide from isopropylidene l - and d -erythrose, using a common strategy.

Diastereocontrol in the intramolecular cycloadditions of 2-substituted-erythro-3,4-isopropylidenedioxyhex-5-enenitrile oxides

Abstract The influence of the 2-substituent on the diastereoselectivity of the intramolecular cycloadditions in a series of 2-substituted-erythro-3,4-isopropylidene-dioxyhex-5-enenitrile oxides, generated in situ from selected sugar derivatives, was examined.

Convenient synthesis and biological profile of 5-amino-substituted 1,2,4-oxadiazole derivatives

We describe herein a convenient straightforward synthesis of 5-amino-substituted 1,2,4-oxadiazoles, upon the reactions of amidoximes with carbodiimides, as well as their further derivatization to acetamides, in good yields. Most of the compounds exhibited in general low interaction with the stable radical 1,1-diphenyl-2-picryl-hydrazyl. Compounds 32 and 39 inhibited significantly soybean lipoxygenase. Selected compounds were screened for their in vivo anti-inflammatory activity using the carrageenin paw edema model and showed significant anti-inflammatory activity (26, 51%). The ability of the compounds to release NO in the presence of a thiol factor has been also investigated.

Bicyclo[3.1.0]hexanes from sugar-derived diazo compounds and iodonium ylides. Diastereocontrol and synthetic applications

Abstract The CuI and Rh 2 (OAc) 4 catalyzed decomposition of ethyl 2-diazo-4,5-isopropylidenedioxy-3-oxo-6-heptenoate results in intramolecular cyclopropanation products with opposite diastereoselectivity. In contrast, decomposition of the respective iodonium ylide can proceed without catalysts to give the cyclopropanation products with diastereoselectivity unchangeable by the presence of CuI and Rh 2 (OAc) 4 , revealing thus, that in this particular case the reaction is an electrophilic addition of the iodonium center to the double bond. The synthetic importance of these reactions has been demonstrated by preparing a number of precursors of cyclopentyl, cyclopropyl and bicyclo[3.1.0]hexyl antiviral carbocyclic nucleosides.

Tetrakisphosphates and Bispyrophosphates of myo-Inositol Derivatives as Allosteric Effectors of Human Hemoglobin: Synthesis, Molecular Recognition, and Oxygen Release

Various 2,5‐ and 1,4‐substituted and unsubstituted myo‐inositol tetrakisphosphates and bispyrophosphates were prepared following a general synthetic pathway. All final compounds were tested for their capability to induce oxygen release from human hemoglobin. Most of these proved to be efficient allosteric effectors, with similar affinities for hemoglobin to that of myo‐inositol hexakisphosphate, which is one of the best known allosteric effectors of hemoglobin. The efficacy was found to be higher for free phosphates than pyrophosphates. As allosteric Hb effectors, these compounds enable enhanced oxygen release. These effects increase with the strength of Hb binding and correspond primarily to electrostatic interactions. Stereochemical and steric factors also play a significant but secondary role in molecular recognition. In view of the central role played by hypoxia in numerous types of diseases, the exploration of myo‐inositol phosphate derivatives represents an important avenue in the search for substances which act on the oxygenation status of tissues and may have significant potential in the discovery and development of novel drug candidates.

Formation of New Alkynyl(phenyl)iodonium Salts and Their Use in the Synthesis of Phenylsulfonyl Indenes and Acetylenes

The preparation of phenylsulfonyl indene derivatives and phenylsulfonyl-acetylenes from readily available alkynyl(phenyl)iodonium tetrafluoroborates and triflates was investigated using phenylsulfinate as nucleophile.

Synthesis of stable aromatic and heteroaromatic sulfonyl-amidoximes and evaluation of their antioxidant and lipid peroxidation activity.

We describe herein the synthesis of stable aromatic and heteroaromatic sulfonyl-amidoximes, from the reaction of amidoximes with the corresponding sulfonyl chlorides, in low to excellent yields. Evaluation of their antioxidant activity has shown that 17 out of 28 compounds highly compete DMSO for hydroxyl radicals, while five of them inhibit lipid peroxidation. Combining the reducing and anti-lipid peroxidation ability it seems that compounds 13 and 31 could be used as lead molecules.

O-Benzoyl pyridine aldoxime and amidoxime derivatives: novel efficient DNA photo-cleavage agents

O-Benzoyl derivatives of meta-, ortho- and para-pyridine aldoximes and amidoximes are novel efficient DNA photo-cleavage agents. In particular O-p-nitro-benzoyl derivatives 4, 8 and 15 were effective at concentrations as low as 1 μM. Both aldoximes and amidoximes were active under aerobic and anaerobic conditions, with a double-stranded to single-stranded DNA cleavage ratio of up to 1. These results give prospects for multiple applications, including phototherapeutic treatment of solid tumors.

Polyphosphates and pyrophosphates of hexopyranoses as allosteric effectors of human hemoglobin: synthesis, molecular recognition, and effect on oxygen release.

Polyphosphorylated and perphosphorylated hexopyranose monosaccharides and disaccharides were synthesized from parent or partially protected carbohydrates as potential allosteric effectors of hemoglobin. A study toward the construction of seven‐ and eight‐membered cyclic pyrophosphates was also performed on the sugars which had the proper orientation, protection, and number of phosphates. All final compounds were tested for their efficiency on oxygen release from human hemoglobin. Several compounds presented higher potency than myo‐inositol hexakisphosphate, which is the most efficient of the known allosteric effectors of hemoglobin. Structure–activity relationships were analyzed. The affinity and efficiency depend on the number of phosphates attached to the carbohydrate skeleton and are related primarily to the number of negative charges present. Other effects operate, but play a lesser role.

Pyridine and p-Nitrophenyl Oxime Esters with Possible Photochemotherapeutic Activity: Synthesis, DNA Photocleavage and DNA Binding Studies

Compared to standard treatments for various diseases, photochemotherapy and photo-dynamic therapy are less invasive approaches, in which DNA photocleavers represent promising tools for novel “on demand” chemotherapeutics. A series of p-nitrobenzoyl and p-pyridoyl ester conjugated aldoximes, amidoximes and ethanone oximes were subjected to UV irradiation at 312 nm with supercoiled circular plasmid DNA. The compounds which possessed appropriate properties were additionally subjected to UVA irradiation at 365 nm. The ability of most of the compounds to photocleave DNA was high at 312 nm, whereas higher concentrations were required at 365 nm as a result of their lower UV absorption. The affinity of selected compounds to calf-thymus (CT) DNA was studied by UV spectroscopy, viscosity experiments and competitive studies with ethidium bromide (EB) revealing that all compounds interacted with CT DNA. The fluorescence emission spectra of the pre-treated EB-DNA exhibited a moderate to significant quenching in the presence of the compounds indicating the binding of the compounds to CT DNA via intercalation as concluded also by DNA-viscosity experiments. For the oxime esters the DNA photocleavage and affinity studies aimed to clarify the role of the oxime nature (aldoxime, ketoxime, amidoxime) and the role of the pyridine and p-nitrophenyl moieties both as oxime substituents and ester conjugates.