Reactions of Doubly Tucked-In Permethyltitanocene with tert-Butanol and Propargyl Alcohol. The Crystal Structures of Unusual Hydrolytic Byproducts

Reactions of double tucked-in permethyltitanocene [Ti{η3:η4-C5Me3(CH2)2}(η5-C5Me5)] (1) with tert-butanol or propargyl alcohol in toluene proceeded sluggishly even with excess of the alcohol and at elevated temperature. The alcoholysis of 1 with tert-butanol afforded [Ti(η5-C5Me5)(Ot-Bu)3] (3) as the major product and Ti(Ot-Bu)4 as the minor one. The other product of the alcoholysis was pentamethylcyclopentadiene. The only isolated crystalline product was the very minor hydrolytic byproduct [{TiIII(η5-C5Me5)2}(μ-O){TiIV(Ot-Bu)3}] (2). The alcoholysis of 1 containing traces of LiI with HOCH2C≡CH, containing apparently more water than t-BuOH, gave an inseparable mixture of oily products from which several crystals of an unintended hydrolytic byproduct [{Ti(η5-C5Me5)(OCH2C≡CH)(μ-O)}3LiI] (4) were isolated. X-ray crystal structures of 2 and 4 were determined.

Synthesis and Crystal Structures of Dinuclear Trichloro(tetramethylcyclopentadienyl)titanium Complexes

Dinuclear half-sandwich complexes [{TiCl3(η5-C5Me4)}2SiMe2] (2) and [{TiCl3(η5-C5Me4SiMe2CH2)}2] (4) were prepared by synproportionation of ansa-titanocene dichlorides [TiCl2{(η5-C5Me4)2SiMe2}] (1) and [TiCl2(η5-C5Me4SiMe2CH2)2] (3), respectively, with TiCl4. Compound 3 was synthesized from 1,2-bis(chlorodimethylsilyl)ethane, 1,2,3,4-tetramethylcyclopentadienyllithium, and [TiCl3(thf)3] by a common procedure. Crystal structures of 2, 3, and 4 were determined by X-ray diffraction analysis.

Preparation and Crystal Structure of Bis(tert-butyltetramethylcyclopentadienyl)dichlorotitanium

[TiCl2(η5-C5Me4t-Bu)2] (1) was prepared by the reaction of [TiCl3(thf)3] with 2 equivalents of Li(η5-C5Me4t-Bu) (made by adding BuLi to a 1.33 molar excess of a mixture of tert-butyltetramethylcyclopentadiene isomers in THF) and subsequent oxidation of the Ti(III) intermediate to 1 by adding aqueous HCl. Neglecting the presence of cyclopentadiene isomers not forming the cyclopentadienide anion in the isomer mixture used for the synthesis of 1 resulted in the formation of hydrolytic product [{TiCl2(η5-C5Me4t-Bu)}2(μ-O)] (2) and a considerable decrease of yield of 1. The half sandwich complex [TiCl3(η5-C5Me4t-Bu)] (3) was obtained by synproportionation of 1 and TiCl4. Crystal structures of 1, 2, and 3 were determined. The electronic absorption spectra of 1 and 3 indicate a stronger electron-donor effect of tert-butyl group compared with methyl group.

Synthesis and Structural Characterization of Functionalized Dimeric Aluminophosphonates and a Monomeric Gallophosphonate Anion

Reaction of t-BuP(O)(OSiMe(3))(OH) with Me(3)Al leads to the formation of [Me(2)Al(mu-O)(2)P(OSiMe(3))(t-Bu)](2) (1) whereas Me(2)AlCl reacts with Ph(2)P(O)(OH) to yield [(Cl)(Me)Al(mu-O)(2)PPh(2)](2) (2). These compounds represent the first examples of functionalized dimeric four-ring type aluminophosphonate systems. The double four-ring type gallophosphonate, namely, [t-BuPO(3)GaMe](4), reacts with n-Bu(4)NHF(2) under ambient conditions, resulting in the formation of a monomeric gallophosphonate [n-Bu(4)N][MeGa[t-BuPO(2)(OH)](3)] (3). These derivatives have been adequately characterized using various spectroscopic techniques and X-ray diffraction studies.

Cytoplasmic sequestration and functional repression of p53 in the mammary epithelium is reversed by hormonal treatment

Proper function of the p53 tumor suppressor gene is critical for inhibiting tumor development in a broad spectrum of tissues. Although the mammary gland is highly susceptible to tumor formation, the functional status of p53 in the normal tissue had not been investigated. Therefore, expression, localization, and activity of p53 were examined in normal mammary tissues. High levels of p53 protein were found expressed in the cytoplasm of the ductal epithelium of the quiescent mammary gland. Ionizing radiation failed to recruit p53 to the nucleus, and p53-dependent responses were minimal. However, transient hormonal stimulation resulted in nuclear accumulation of p53, an induction of p21/WAF1, and a 5-fold increase in apoptosis after ionizing radiation. Therefore, the functional state of wild-type p53 in the mammary epithelium can be regulated by hormonal stimuli.

Expression of MDM2 during mammary tumorigenesis

The MDM2 oncoprotein encodes a 90 kDa nuclear phosphoprotein capable of abrogating the growth suppressive functions of p53 and pRb tumor suppressor proteins by direct interaction. Alternative splicing of MDM2 protein coding sequences has been documented during tumor progression in human ovarian and bladder carcinomas. The aim of this study was to determine whether alternative splicing of MDM2 occurs during breast tumorigenesis in mice and humans and whether protein coding sequences were affected. Specimens representing normal and malignant breast tissues from the murine D2 mammary tumor model system and human breast carcinomas were examined. Three distinct mdm2 mRNA transcripts of 3.3, 1.6 and 1.5 kb were detected in normal and malignant murine mammary tissues by Northern blot analysis using a full-length mdm2 cDNA probe. Additional Northern blot analysis using a probe derived from exon 12 of murine mdm2 demonstrated that the 1.5 and 1.6 kb transcripts lack sequences encoding the C-terminus of the protein. No evidence of internal deletions of protein coding sequences of mdm2 was detected in any of the normal mammary tissues or D2 murine mammary tumors examined by reverse transcription PCR (RT-PCR). Three distinct MDM2 transcripts of 6.7, 4.7 and 1.9 kb were detected in malignant human breast tissue by Northern blot analysis using a cDNA probe specific for the complete open reading frame of human MDM2. However, a cDNA probe specific for the last exon of human MDM2 hybridized only to the 6.7 and 4.7 kb transcripts, demonstrating that the 1.9 kb transcript lacked protein coding sequences contained in exon 12. Similarly, no internal deletions were detected in a panel of malignant human breast tissues using RT-PCR and analogous primers within human MDM2. Therefore, breast tumors differ from other solid tumors reported previously in that no internal deletions of MDM2 protein coding sequences were observed. However, the data document the presence of multiple MDM2 mRNA transcripts in both normal and malignant breast tissues. A subset of MDM2 transcripts were shown to lack the last exon which contains sequences coding for the RING and zinc fingers and domains which are targets for caspase-3 mediated proteolytic degradation and are required to target p53 for proteosomal degradation.

Regulation of p53 and its targets during involution of the mammary gland

Post-lactational involution of the mammary gland provides a system in which to study the expression and function of genes that regulate apoptosis in the context of a normal tissue. The functions of the p53 tumor suppressor gene have been extensively studied as a mediator of apoptosis in response to DNA damage, but its regulation in normal physiologic processes has been poorly characterized. Expression of p53 mRNA was shown to be among the first genes to be induced in mammary tissue following weaning of neonates. Although involution proceeds in the absence of a functional p53 gene, it is delayed compared to normal individuals. Therefore, involution can be viewed as biphasic with initial responses being sensitive to p53, whereas secondary responses being p53-independent. These observations can be exploited to determine the subset of genes that are p53-responsive and that mediate the effects of p53 in normal mammary tissue.

Delayed involution of the mammary epithelium in BALB/c-p53null mice

In mammals, weaning of neonates and subsequent milk stasis initiates removal of the secretory epithelium of the mammary gland by apoptosis. The p53 tumor suppressor gene is induced rapidly following weaning of neonates, but its role in the process of involution has not been defined. Therefore, experiments were performed to identify the cell types in which the p53 gene is expressed during involution and determine the consequences of its absence in BALB/c-p53null mice. Both p53 mRNA and protein were detected in the mammary epithelium within 48 h following weaning and resulted in an eightfold increase in levels of p21WAF1 mRNA. Induction of p21WAF1 mRNA was absent in BALB/c-p53null mice, and therefore, was shown to be p53-dependent. The BALB/c-p53null mice exhibited delayed involution of the mammary epithelium, as measured by 60% greater epithelial area compared to BALB/c-p53(wt) mice through 5 days post-weaning. The delay was transient with no differences being apparent at 7 days post-weaning. Expression of the stromal protease stromelysin-1 was unaffected by the absence of p53 suggesting that stromal responses were intact. These data demonstrate that p53 participates in the first stage of involution initiated by the epithelium itself, but does not affect the second phase during which stromal proteases are induced.