Correlation Between Chemical Shifts (31P) and Steric Parameters of Phosphametallacycloalkanes

Abstract

The X-ray structures of the phosphametallacycloalkanes 1¹

were investigated to understand the anomalous chemical shift behavior of the phosphorus incorporated in the ringsystem. The ³¹P chemical shifts could not be related to bond angles and to Tolman angles. An electronic contribution to the δP value could be excluded, while the torsional angle effect proved to be the dominant factor.     

Preparation,Properties and Complexation Behaviour of P,P-Di-tert. Butylphosphinothioic Amides

Abstract

Starting from tBu₂PCl, the title compounds tBu₂P(S)NHR′ (R′= Me Et, iPr, tBu) may be easily prepared according to With R′=tBu the amine has to be substituted by its Li-salt [tBuNH]^?Li^+.     

Reactions of Unsaturated Phosphonic Acids with 2-Aminopyridine

Abstract

Different unsaturated phosphonic acids of the general formula (R=C1, OCH₃, OH, NMe₂, C₆H₅; R′=C1, OCH₃, H, NMe₂) have been prepared starting from propargyl alcohol. Reaction of chlorophosphonic acids with 2-amino-pyridine yields phosphoramidates, which in the next step undergo a base-catalyzed cyclization by addition of the ring nitrogen across the unsaturated bond, leading to the unstable derivative 1. In the case of the allenic phosphonic acid in which R=R′=NMe₂, the NH₂ group of 2-aminopyridine adds first to the allenic system yielding an enamine, which on heating cyclizes to give a new phosphorus-nitrogen heterocyclic system 2.     

Phosphorus Containing Ions with Unconventional Structure: El-Fragmentation of Et3P(S)

Abstract

Gas phase ion structures often do not correlate with those of their corresponding neutrals and many ions with unconventional structures have been found to be stable in the gas phase in contrast to their neutral counterparts. Thus, radical ions (a) and (b)

are formed under EI-conditions by consecutive elimination of C₂H₄ from ionized triethylphosphanesulfide Et₃P(S). (a) contains tricoordinated phosphorus while the structure of (b) corresponds to an ionized adduct of H₂S and the “phosphinidene” Et - P. The structures have been determined on the basis of collisional activation and metastable ion spectra as well as H/D-exchange reactions. Results of semiempirical MO-calculations (MNDO) are reported.     

Regioselective Intramolecular Carbon-Hydrogen Insertion in Copper-Catalyzed Carbenoid Decompositions of cis-1-Methyl-3-Arylcyclohexane-1-Diazomethyl Ketones : Some Synthetic Applications

Recently, we have developed¹ a new route for the stereo-specific introduction of an angular carboxyl or functionalized methyl groups² in a rigid hydrophenanthrene moiety. The key step in this approach is a regioselective intramolecular α-keto carbenoid insertion across the benzylic C-H bond (at C-4a) in CuSO₄-catalyzed thermal decomposition of the diazoketones and to the corresponding tetracyclic ketones and in moderate to good yields. A modified procedure³ of carbenoid decomposition of these diazoketones, in the presence of Cu₂O under irradiation with tungsten filament lamp, improves the yields of the desired C-H insertion products. Thus, the ketones and have been prepared now in consistently higher yields (53-55%) from the pure diazoketones , m.p. 125-127°, and , m.p.     

Conformational Properties of the Phosphate Rings of Neutral Phosphoramidate Derivatives of Ribo- and 2′-Deoxyribonucleoside Cyclic 3′,5′-Monophosphates

Abstract

An investigation of the effects of changing the nature of X, nitrogen base (B), and amino substituent (R₂N) on the equilibrium 1?2 was carried out.

The influence of the above structural changes on the time-averaged coupling constants J_AP and J_BP, determined at 300 MHz, were used to follow changes in K_eq. With constant R₂N, small effects from variation of X and B were found. A large range in K_eq arose from changes in the steric size of R₂N. These results will be related to the question of the ease of chair to twist interconversion of the phosphate ring essential to the biological activities of the naturally occurring diesters, cAMP and cGMP.     

O-[7-(1-Methylquinolinium)]-1,3,2-Dioxaphosphorinane 2-Oxide Iodide: A Reversible Anti-acetylcholinesterase and Irreversible Anti-butyrylcholinesterase Organophosphorus Ester

Abstract

Although cyclic organophosphates(OP) esters (I) and their open-chain analogs (II) demonstrate similar reactivity of a P atom towards nucleophilic displacement in aqueous solutions, the open-chain analogs (II) are thousand times more active as inhibitors of acetylcholinesterase(AChE). In order to explain the poor anti-ChE activity of I, a covalent molecular combination,IV, of the cyclic phosphate and an extremely effective leaving group (III) was prepared and evaluated. The new compound, IV, was found to inhibit progressively horse-serum butyrylcholinesterase(BuChE)at t^1/2=15 min.(2.9μM, pH 7.0, 25°) whereas no progressive inhibition could be demonstrated for eel AChE incubated for several hrs under the same experimental conditions.Eel AChE was inhibited reversibly by IV with affinity constant,KI=1.3×10^?6 M. These findings may suggest the following: a. In order to compensate for overcrowding of the AChE active-site by large substituents it is essential to maintain flexibility of the four ligands attached to the P atom. It is further infered that cyclization does not permit such flexibility. b. BuChE differ considerably from AChE in the ability of the enzyme to provide simultaneous four-site interaction with tetrahedral OP inhibitors.