Balram Dhawan

Calixarenes 9 : Conformational isomers of the ethers and esters of calix[4]arenes

Abstract Calix[4]arene (1A), p-t-butylcalix[4]arene (1B), and p-allylcalix[4]arene (1C) have been converted to various derivatives, including the methyl, ethyl, allyl, benzyl and trimethylsilyl ethers and the acetates. Although the parent calixarenes exist preferentially in the cone conformation, they are conformationally flexible and at room temperature interconvert at a rate of ca 100 sec−1. All but the methyl ethers, on the other hand, are conformationally rigid at room temperature. The preferred conformations in most cases are the cone and partial cone, depending on the derivative formed (i.e. methyl and ethyl ethers favor the partial cone; benzyl and trimethylsilyl ethers favor the cone). In the cases of the allyl ethers and the acetates the p-substituents appear to influence the conformational outcome (i.e. 1A and 1B form the allyl ethers in the partial cone and cone conformation, respectively; 1A and 1B form the acetates in the 1,3-alternate and partial cone conformation, respectively). The conformationally rigid calixarene derivatives in the cone and partial cone conformations belong to the small group of synthetic compounds that contain a permanent cavity (a “changeless calix”) whose dimensions are large enough to encapsulate other molecules.

OPTICALLY ACTIVE 1-AMINOALKYLPHOSPHONIC ACIDS

Abstract 1-Aminoalkylphosphonic acids 1 as analogs of 1-amino-carboxylic acids are important because of their potential biological activity. These act as substrates or inhibitors of enzymes involved in the metabolism of amino acids. Several phosphono dipeptides and oligopeptides are known to repress bacterial growth. Many of these studies have been carried out using racemic l-amino- alkylphosphonic acids 1 although in several cases their activity has been shown to depend upon their absolute c~nfiguration. One such example is the high antibacterial activity of alafosfalin 2, N-(L-alany1)-L-1-aminoethylphosphonic acid, as compared to that of the other diastereoisomers. Alafosfalin 2 has been shown to act by facilitated transport into the bacterial cell wall where it is cleaved enzymatically to L-1-aminoethylphosphonic acid la which inhibits alanine racemase and related processes by simulating L-alanine. The analgesic activity of enkephalin analogs containing aminophosphonic acid residues at C-terminal posit...

Rearrangement of a Di-t-butyl Aryl Phosphate to a Di-t-butyl (2-Hydroxyaryl) phosphonate. A Convenient Preparation of (2-Hydroxyphenyl)-and (2-Hydroxy 5-Methoxy Phenyl) Phosphonic Acids

Abstract (2-Hydroxyphenyl) phosphonic acid 4a phosphorus analogue of salicylic acid is to date a difficultly accessible compound. The two reported preparations of 4a start with difficultly available starting materials and give poor overall yields. Whereas Freedman1 obtained 4a in 16% overall yield starting with (2-nitro phenyl) benzyl ether and reported a melting point of 124–127°C, Lukin and Kalanina2 claimed to have obtained 4a in 41% yield by the treatment of (2-brornophenyl) phosphonic acid with aq. ammonia in presence of cuprous oxide3 and reported a melting point of 178–179°C. In addition to the difference in melting point, the products obtained by the above two methods seemed to differ in their solubility in water.

Metallation Induced Rearrangement of Triarylphosphates to Tris (2-Hydroxyaryl) Phosphine Oxides

Abstract A novel one step conversion of triaryl phosphates to tris (2-hydroxyaryl) phosphine oxides involving a metallation induced triple migration of phosphorus from O°C is reported.

REACTION OF PENTAERYTHRITOL WITH DIETHYL PHOSPHOROCHLORIDATE PENTAERYTHRITOL BIS-, TRIS- AND TETRAKIS(DIHYDROGEN PHOSPHATES)

Abstract Reaction of pentaerythritol 1 with 1, 2 or 3 equivalents of diethyl phosphorochloridate 2 yielded pentaerythritol tris(diethyl phosphate) 5. Treatment of pentaerythritol with 4 or more equivalents of 2 gave pentaerythritol tetrakis(diethyl phosphate) 6. Transesterification of 5 and 6 with trimethylsilyl chloride and sodium iodide in acetonitrile followed by treatment with water gave pentaerythritol tris (dihydrogen phosphate) 7 and pentaerythritol tetrakis(dihydrogen phosphate) 8 respectively. Pentaerythritol bis(dihydrogen phosphate) 9 was prepared by the hydrolysis of 3,9-dichloro-2,4,8,10-tetraoxa-3,9-diphosphaspiro [5,5] undecane 3,9-dioxide 10. The compounds 7,8 and 9 were isolated as anilinium salts and characterized by 1H, 13C and 31P NMR spectra.