An Overview on Steroids and Microwave Energy in Multi-Component Reactions towards the Synthesis of Novel Hybrid Molecules.

In recent years, hybrid systems are gaining considerable attention owing to their various biological applications in drug development. Generally, hybrid molecules are constructed from different molecular entities to generate a new functional molecule with improved biological activities. There already exist a large number of naturally occurring hybrid molecules based on both non-steroid and steroid frameworks synthesized by nature through mixed biosynthetic pathways such as, a) integration of the different biosynthetic pathways or b) Carbon- Carbon bond formation between different components derived through different biosynthetic pathways. Multicomponent reactions are a great way to generate efficient libraries of hybrid compounds with high diversity. Throughout the scientific history, the most common factors developing technologies are less energy consumption and avoiding the use of hazardous reagents. In this case, microwave energy plays a vital role in chemical transformations since it involves two very essential criteria of synthesis, minimizing energy consumption required for heating and time required for the reaction. This review summarizes the use of microwave energy in the synthesis of steroidal and non-steroidal hybrid molecules and the use of multicomponent reactions.

Large reverse saturable absorption under weak continuous incoherent light.

In materials showing reverse saturable absorption (RSA), the optical absorbance increases as the power of the light incident on them increases. To date, RSA has only been observed when very intense light sources, such as short-pulse lasers, are used. Here, we show that hydroxyl steroidal matrices embedding properly designed aromatic molecules as acceptors and transition-metal complexes as donors exhibit high RSA on exposure to weak incoherent light at room temperature and in air. Accumulation by photosensitization of long-lived room-temperature triplet excitons in acceptors with a large triplet-triplet absorption coefficient allows a nonlinear increase in absorbance also under low-power irradiation conditions. As a consequence, continuous exposure to weak light significantly decreases the transmittance of thin films fabricated with these compounds. These optical limiting properties may be used to protect eyes and light sensors from exposure to intense radiation generated by incoherent sources and for other light-absorption applications that have not been realized with conventional RSA materials.

Testicular steroidogenesis is not altered by 137 cesium Chernobyl fallout, following in utero or post-natal chronic exposure.

The testis is especially sensitive to pollutants, including radionuclides. Following the Chernobyl nuclear power plant accident, several of these radionuclides were emitted and spread in the environment. Subsequently, children presented some disruptions of the endocrine system. To determine whether these disruptions were due to 137 cesium ((137)Cs) exposure, the effects of chronic contamination with low doses of (137)Cs in utero or from birth on testicular steroidogenesis in rats were studied. Contamination was continued for 9 months. No modification was observed in circulating level of hormones (17beta-estradiol, testosterone, follicle-stimulating hormone, luteinizing hormone) following in utero or post-natal contamination. Expression of several genes involved in testicular steroidogenesis was affected (cyp19a1, fxr, sf-1), without modification of protein expression or activity. Our results suggest that growing organisms may be affected at the molecular level by (137)Cs contamination at this post-accidental dose.

Density functional theory as a tool for the structure determination of radiation-induced bioradicals.

The use of density functional methods for the elucidation of the structure of radiation-induced bio-radicals by comparison of computed and experimental EPR properties is discussed. Three case studies, radiation induced radicals of the amino acid alanine, steroid hormones and beta-D-fructose, with increasing degree of uncertainty about the proposed radical structures, are investigated. Next to the analysis of the isotropic and anisotropic components of the hyperfine tensor, also the direction cosines of the principal axes of this tensor were investigated in greater detail in the case of the beta-D-fructose radicals. Since all radicals considered in this contribution are formed in a solid matrix, also the question as to how to incorporate the effect of the molecular environment is addressed. It is concluded that the methodology outlined represents a powerful tool to aid experimentalists in the assignment of the contributions of various radicals contributing to the observed EPR spectra.

Microwave-assisted Stille-coupling of steroidal substrates.

Steroidal dienes were synthesised by Stille-coupling of the corresponding alkenyl iodides with vinyltributyltin under microwave irradiation in a domestic microwave oven in drastically reduced reaction times. Rate acceleration was observed also in the one-pot Stille-coupling-Diels-Alder reaction of 17-iodo-5alpha-androst-16-ene. Stereoselectivity of cycloaddition was slightly improved with diethyl maleate as the dienophile, compared to that achieved with thermal heating.

Noncommunicating photoreaction paths in some pregna-1,4-diene-3,20-diones.

The photochemistry of three pregna-1,4-diene-3,20-diones bearing a hydroxy or alkoxy group at C(17) (4-6) has been examined. Irradiation at 254 or 366 nm, where absorption by the cross-conjugated ketone moiety in ring A is predominant or exclusive, causes the 'lumiketone' rearrangement of this chromophore in low to medium quantum yield (Phi(r) 0.05 to 0.31). On the contrary, irradiation at 310 nm, where the isolated ketone at C(20) absorbs a large portion of light causes Norrish-I fragmentation of that chromophore with a higher Phi(r) (0.11-0.83). This leads to end-products arising from the conversion of the C(17) alkyl radical, in a way depending on the structure and the medium (reduction by hydrogen donating solvent, addition of oxygen when present). No intramolecular T-T energy transfer between the separated chromophores occurs. The 'lumiketone' rearrangement occurs independently from the irradiation wavelength (Phi(r) 0.06-0.18) with the strictly related androsta-1,4-dien-3-one 8 lacking the C(20) ketone function.

EPR/ENDOR investigations of gamma-irradiated steroid hormone single crystals.

The molecular structure of free radicals formed in certain gamma-irradiated steroid hormones and cholesterol determined by electron spin resonance (ESR) and electron nuclear double resonance studies has been reviewed. The influence of intermolecular interactions and hydrogen bonds on the structure of the radicals formed, as well as the effect of substitution of hydroxyl group on the alpha-hyperfine splitting tensor have also been analyzed.