The two new sterically demanding secondary phosphines (C 6 H 4 -2-OMe)RPH ( 1a) and (C 6 H 3 -2-OMe-3-Me)RPH (1b) [R ) CH(SiMe 3 ) 2 ] are synthesized by the reaction of RPCl 2 with 1 equiv of LiC 6 H 4 -2-OMe or LiC 6 H 3 -2-OMe-3-Me, respectively, followed by in situ reduction with LiAlH 4 . Metalation of 1 with Bu n Li, followed by metathesis with KOBu t , yields the potassium salts K{PR(C 6 H 4 -2-OMe)} (2a) and K{PR(C 6 H 3 -2-OMe-3-Me)} (2b). The reaction of K{PR(C 6 H 3 -2-OMe-3-Me)} with YbI 2 yields the diphosphide complex [Yb II {PR(C 6 H 3 -2-OMe-3-Me)} 2 (THF) 2 ] (3), in which the phosphides act as P,O-chelating ligands. In contrast, reaction of K{PR(C 6 H 4 -2-OMe)} with YbI 2 under similar conditions yields the unexpected alkoxophosphide complex [Yb II {PR(C 6 H 4 -2-O)}(THF)] 4 ‚4Et 2 O (4), via an unusual ligand cleavage reaction involving the transfer of a methyl group from oxygen to phosphorus. Compounds 1-4 have been characterized by elemental analyses and multinuclear NMR spectroscopy and compounds 3 and 4 by X-ray crystallography. Compound 3 is monomeric in the solid state, with a distorted all-trans-octahedral geometry about the Yb center; compound 4 crystallizes as an unprecedented tetrameric cluster containing a Yb 4 O 4 cuboidal core. Multi-element NMR spectroscopy suggests that 4 maintains an oligomeric structure in THF solution. The P-containing side product formed in the synthesis of 4 has been isolated and identified as (Me)PR(C 6 H 4 -2-OMe) by comparison of its NMR and mass spectra with those of an authentic sample.

QUTR (qutR-encoded transcription-repressing protein) is a multi-domain repressor protein active in the signal-transduction pathway that regulates transcription of the quinic acid utilization (qut) gene cluster in Aspergillus nidulans. In the presence of quinate, production of mRNA from the eight genes of the qut pathway is stimulated by the activator protein QUTA (qutA-encoded transcription-activating protein). Mutations in the qutR gene alter QUTR function such that the transcription of the qut gene cluster is permanently on (constitutive phenotype) or is insensitive to the presence of quinate (super-repressed phenotype). These mutant phenotypes imply that the QUTR protein plays a key role in signal recognition and transduction, and we have used deletion analysis to determine which regions of the QUTR protein are involved in these functions. We show that the QUTR protein recognizes and binds to the QUTA protein in vitro and that the N-terminal 88 amino acids of QUTR are sufficient to inactivate QUTA function in vivo. Deletion analysis and domain-swap experiments imply that the two C-terminal domains of QUTR are mainly involved in signal recognition.

No abstract

No abstract