Ousmane Diouf

The thioacetate approach to the synthesis of the side chain of vitamin D metabolites and analogues

We describe an efficient synthesis of thia analogues of the vitamin D side chain that is based on the in situ generation of a thiolate anion and its alkylation with electrophiles.

Combined uses of water-table fluctuation (WTF), chloride mass balance (CMB) and environmental isotopes methods to investigate groundwater recharge in the Thiaroye sandy aquifer (Dakar, Senegal)

The quaternary sandy sediments which cover most part of the Cap Vert peninsula bear considerable groundwater resources. The aquifer lying beneath a densely populated suburb zone is encountered with major issues such as induced recharge from anthropogenic surface derived pollution and rising water table to ground surface. The present study was aimed at investigating the recharge in the unconfined aquifer of Thiaroye zone using both water table fluctuation (WTF), chloride mass balance (CMB) methods and environmental isotopes. Seasonal fluctuations of groundwater in response to precipitation are monitored during time period (2010 to 2011) using “Thalimede Orpheus mini” recorders in two piezometers (P3-1 and PSQ1) as well as long term record. Chemical and isotopic characterization of groundwater, rainfall and the unsaturated zone were also carried out using a network of 48 points consisting of 8 rainfall stations, 10 unsaturated zone profiles and 30 dug wells, boreholes and piezometers. The concentrations of chloride in rainwater are between 3.2 and 53.4 mg/L. These unsaturated zone profiles range from 65 and 572 mg/L. The recharge obtained by WTF method ranged between 18 and 144 mm during the rainy season (June to October), whereas the recharge given by CMB method ranged between 8.7 and 73 mm/year. The Thiaroye aquifer recharge obtained from these different methods also showed relatively similar range values. In this study, the WTF method applied computes both infiltration from rainwater and domestic waste water, while the CMB method estimates potential recharge from rainwater. Therefore, in the urban area, the CMB method cannot be applied due to the chloride input from waste water infiltration. Key words : Thiaroye basin, recharge, isotopes, chloride mass balance (CMB), quaternary sandy aquifer (Dakar).

Synthesis and Use of Imidazolium Bound Rose Bengal Derivatives for Singlet Oxygen Generation

We describe the preparation and use of two new imidazolium-bound Rose Bengal derivatives for singlet oxy- gen generation. Photolysis of oxygen-saturated solution of furan rings in the presence of the imidazolium-bound sensitiz- ers provides the corresponding butenolides. The sensitizers could be recovered after the oxidation reaction.

1,5-Bis(2-hy-droxy-3-meth-oxy-benzyl-idene)carbonohydrazide methanol 0.47-solvate.

In the title compound, C17H18N4O5·0.47CH3OH, the virtually planar (r.m.s. deviation = 0.128 Å) carbonohydrazide molecule is located on a twofold axis and conformation of its C=N bonds is E. There are short intramolecular O—H⋯N hydrogen bonds between the hydroxy groups and hydrazide N atoms. In the crystal, bifurcated N—H⋯(O,O) hydrogen bonds assemble the carbonohydrazide molecules into a three-dimensional network. There are C 2 symmetric voids in this network, 47% of which are occupied by disordered methanol molecules.

3,3'-Dibenzoyl-1,1'-(3,6-dioxaoctane-1,8-di-yl)dithio-urea.

In the molecule of the title compound, C22H26N4O4S2, the central O—CH2—CH2—O chain adopts a synclinal conformation [torsion angle = 65.0 (2)°]. The crystal structure is stabilized by intramolecular N—H⋯O=C and intermolecular N—H⋯O—C hydrogen bonds.

Bis(2-{[2-(2-hy­droxy­benzyl­amino)­eth­yl]amino­meth­yl}phenolato-κ3N,N′,O1)cobalt(III) nitrate monohydrate

In the title compound, [Co(C16H19N2O2)2]NO3·H2O, the CoIII ion is located on an inversion center and is six-coordinated by two phenolate O atoms and four amino N atoms from two diamine ligands, forming an octahedral geometry. The water molecule and the nitrate anion are located close to an inversion center, and are thus equally disordered by symmetry. The crystal packing is stabilized by intermolecular O—H⋯O hydrogen bonds involving the uncoordinated water molecule and the free phenol hydroxyl group with the nitrate anion. N—H⋯O hydrogen bonds involving the amino groups and the nitrate anions connect the complex molecules along the c axis.

The furan approach to the synthesis of natural products having highly substituted cyclic ether moieties

Highly substituted cyclic ethers occur in many natural products exhibiting important biological activities.1–6 These units can be found in monocyclic as well as in polycyclic structures some of them are depicted in Figure 1. Due to the biological importance of these compounds, they have been the targets of numerous synthetic studies.7–13 In our research group we have developed a new methodology for the synthesis of oxacyclic compounds using furan as starting material.14–27 The scope and limitations of this very powerful methodology are being determined.

OCT Analogues Part 2. Acetylene in the Synthesis of Useful Building Blocks for Analogues of OCT Modified at C-20, C-21, and the D-Ring

Diols 11 and 12, potential building blocks for the synthesis of 20-epi-OCT, and analogues modified at C-21 and the D-ring, were efficiently synthesized using Pd(II)-catalyzed oxidative rearrangement of propargylic acetate7.