Assignment of the absolute configuration of hydroxy- and aminophosphonates by NMR spectroscopy

Phosphonate analogues of amino- and hydroxy acids have received considerable attention in bioorganic and medicinal chemistry due to their unique activities as peptidomimetics, being known as inhibitors of such enzymes as human renin, HIV protease and polymerase, leucine aminopeptidase and serine proteases. They have also been exploited as haptens for catalytic antibody research, herbicides, antibiotics, antiviral and anticancer agents and neuromodulators. Therefore, the demand for the asymmetric synthesis of hydroxy- and aminophosphonates should be accompanied by reliable methods for their absolute configuration assignment. NMR spectroscopy is one of the most commonly used techniques for the assignment of absolute configuration of different classes of compounds. This report describes the principles and practical aspects of applying chiral discriminating agents for the assignment of absolute configuration of 1- and 2-hydroxyphosphonates and 1- and 2-aminophosphonates by NMR spectroscopy. The report is organized in sections discussing the types of the chiral discriminating agents (including the models used for configuration assignment, if this was proposed) and the scope of their applications (with the list of all the examples of hydroxy- and aminophosphonates examined by this method). The application of the chiral derivatizing agents (CDA) and chiral solvating agents (CSA) used for these purposes, such as α-methoxy-α-(trifluoromethyl)phenylacetic acid (MTPA), α-methoxyphenylacetic acid (MPA), amino acids, diazaphospholidine, camphanic acid, naproxen, quinine and t-butylphenylphosphinothioic acid is discussed. Easy access to the selected values of the NMR chemical shifts observed for the diastereomeric species of the tested hydroxy- and aminophosphonates examined, will enable the reader to compare trends observed in spectra and subsequent absolute configuration assignment. In addition, any available complementary data confirming the configuration established by NMR (X-ray, chemical correlations, optical rotation) is also provided.     

Letter: Note on the Luminosity Distance

We re-derive a formula relating the areal and luminosity distances, entirely in the framework of the classical Maxwell theory, assuming a geometric-optics type condition.     

Singularity spectra of strongly inhomogeneous multifractals

Generalized multifractal formalism is used to study singularity spectra of strongly inhomogeneous multifractals characterized by coarse-grained probability measures with zero minimal and/or infinite maximal H?lder exponents. Due to involving two additional types of scaling indices, the generalized formalism is shown to be able to describe complex multifractal objects by families of bivariate spectra rather than familiar single spectra of singularity strengths of one type, providing a more complete and adequate characteristics of such objects. It is proved that the families of extended singularity spectra can reveal unusual forms with many maxima, reflecting complex scaling structures of strongly inhomogeneous multifractals. Received 25 April 2001 and Received in final form 26 February 2002     

Balance functions from a thermal model

A calculation of the pion balance functions in a thermal model is presented. The total result consists of resonance and non-resonance parts. A satisfactory agreement with the data on Au+Au collisions at v[s_NN] = 130 GeV is found.     

Direct product of affine partial linear spaces, general approach

We analyze foundations of the construction of the direct product of affine partial linear spaces, as defined by Johnson and Ostrom. Fundamental preservation theorems are proved, and the role of some of frequently used affine axioms in the context of this theory is discussed.     

Material Symmetry in a Theory of Continuously Defective Crystals

We propose that a particular group, which depends on the dislocation density tensor, be adopted as material symmetry group for some classes of defective crystals, and give motivation for this proposal.     

An enantiopure diselenide based on a chiral bicyclic backbone—synthesis and configuration assignment

An enantiomerically pure diselenide containing two chiral bicyclic subunits was prepared from the respective halides. The stereochemical outcome of the reaction was established via NMR spectroscopy and X-ray diffraction measurements.