Kloning Manusia

In the last few years, very rapid progress in the cloning technology and its development towards human cloning has become a hotly-debated issue. Cloning, which is the process of formation of a number of individuals with the same genetic structure, can be done by means of embryo-splitting method and nuclear transfer. Human cloning through the nuclear transfer method is directed towards two purposes, i.e. reproduction and therapy. The relatively new transgenic technology can be combined with the cloning technique to produce clones with new genes. However, pros and cons arise concerning the development of research on human cloning, particularly cloning for reproductive purposes. Therefore, there is need for a moratorium period before human cloning can be performed in order that solutions for all kinds of problems related to safety and ethics can be found

Stereocontrolled Synthesis of 1,2- and 1,3-Diamine Building Blocks from Aziridine Aldehyde Dimers

Vicinal aziridine-containing diamines have been obtained with high <i>syn</i>-stereoselectivity from readily available aziridine aldehyde dimers in the Petasis borono-Mannich reaction. Subsequent solvent- and/or nucleophile-dependent ring-opening of the aziridine ring yields functionalized 1,2- and 1,3-diamines with high regioselectivity. The ring opening is also influenced by the substitution at the C3 position of the aziridine. A mechanistic rationale for the highly <i>syn</i>-selective three-component reaction is proposed

Stereocontrolled Synthesis of 1,2- and 1,3-Diamine Building Blocks from Aziridine Aldehyde Dimers

Vicinal aziridine-containing diamines have been obtained with high <i>syn</i>-stereoselectivity from readily available aziridine aldehyde dimers in the Petasis borono-Mannich reaction. Subsequent solvent- and/or nucleophile-dependent ring-opening of the aziridine ring yields functionalized 1,2- and 1,3-diamines with high regioselectivity. The ring opening is also influenced by the substitution at the C3 position of the aziridine. A mechanistic rationale for the highly <i>syn</i>-selective three-component reaction is proposed

A Study of Boratriazaroles: An Underdeveloped Class of Heterocycles

Boratriazaroles were discovered in the late 1960s, and since then, a variety of substituted boratriazarole derivatives have been prepared. However, no study has compared the properties of these BN heterocycles with their carbon-based analogues. In this work, we have prepared a series of boratriazarole derivatives and have investigated how structural variations in the five-member heterocycle affect photophysical and electronic properties. Boratriazaroles exhibit absorption and emission spectra comparable to those of their azacycle analogues but have a markedly lower quantum yield. The quantum yield can be increased with the incorporation of a 2-pyridyl substitution on the boratriazaroles, and the structural and optoelectronic properties are further influenced by the nature of the B-aryl substituent. Introducing an electron-deficient <i>p</i>-cyano group on the B-phenyl substituent creates a twisted intramolecular charge transfer state that causes a large Stokes shift and positive solvatochromism. Our work should serve to guide future synthetic efforts toward the application of boratriazaroles in materials science

Condensation-Driven Assembly of Boron-Containing Bis(Heteroaryl) Motifs Using a Linchpin Approach

Herein, we describe the bromomethyl acyl boronate linchpin–an enabling reagent for the condensation-driven assembly of novel bis­(heteroaryl) motifs. This building block is readily accessible from commercially available starting materials. A variety of 2-amino- and 2-methylpyridines were reacted with MIDA-protected bromomethyl acylboronate to afford 2-boryl imidazo­[1,2-<i>a</i>]­pyridine and 2-boryl indolizine derivatives, respectively, in excellent yields. Subsequent condensation with hydroxyamidines and hydrazonamides converted the intermediate heterocycles into novel boron-containing bis­(heteroaryl) units characterized by high thermal stability

Condensation-Driven Assembly of Boron-Containing Bis(Heteroaryl) Motifs Using a Linchpin Approach

Herein, we describe the bromomethyl acyl boronate linchpin–an enabling reagent for the condensation-driven assembly of novel bis­(heteroaryl) motifs. This building block is readily accessible from commercially available starting materials. A variety of 2-amino- and 2-methylpyridines were reacted with MIDA-protected bromomethyl acylboronate to afford 2-boryl imidazo­[1,2-<i>a</i>]­pyridine and 2-boryl indolizine derivatives, respectively, in excellent yields. Subsequent condensation with hydroxyamidines and hydrazonamides converted the intermediate heterocycles into novel boron-containing bis­(heteroaryl) units characterized by high thermal stability

Condensation-Driven Assembly of Boron-Containing Bis(Heteroaryl) Motifs Using a Linchpin Approach

Herein, we describe the bromomethyl acyl boronate linchpin–an enabling reagent for the condensation-driven assembly of novel bis­(heteroaryl) motifs. This building block is readily accessible from commercially available starting materials. A variety of 2-amino- and 2-methylpyridines were reacted with MIDA-protected bromomethyl acylboronate to afford 2-boryl imidazo­[1,2-<i>a</i>]­pyridine and 2-boryl indolizine derivatives, respectively, in excellent yields. Subsequent condensation with hydroxyamidines and hydrazonamides converted the intermediate heterocycles into novel boron-containing bis­(heteroaryl) units characterized by high thermal stability

Expanding the Steric Coverage Offered by Bis(amidosilyl) Chelates: Isolation of Low-Coordinate <i>N</i>-Heterocyclic Germylene Complexes

The synthesis and coordination chemistry of a series of dianionic bis­(amido)­silyl and bis­(amido)­disilyl, [NSiN] and [NSiSiN], chelates with N-bound aryl or sterically modified triarylsilyl (SiAr₃) groups is reported. In order to provide a consistent comparison of the steric coverage afforded by each ligand construct, various two-coordinate <i>N</i>-heterocyclic germylene complexes featuring each ligand set were prepared and oxidative S-atom transfer chemistry was explored. In the cases where clean oxidation transpired, sulfido-bridged centrosymmetric germanium­(IV) dimers of the general form [LGe­(μ-S)]₂ (L = bis­(amidosilyl) ligands) were obtained in lieu of the target monomeric germanethiones with discrete GeS double bonds. These results indicate that the reported chelates possess sufficient conformational flexibility to allow for the dimerization of LGeS units to occur. Notably, the new triarylsilyl groups (4-RC₆H₄)₃Si (R = ^<i>t</i>Bu and ^<i>i</i>Pr) still offer considerably expanded degrees of steric coverage relative to the parent congener, SiPh_3, and thus the use of substituted triarylsilyl groups within ligand design strategies should be a generally useful concept in advancing low-coordination main group and transition-metal chemistry