Stereospecific Cu(I)-Catalyzed C-O Cross-Coupling Synthesis of Acyclic 1,2-Di- and Trisubstituted Vinylic Ethers from Alcohols and Vinylic Halides

CuI and trans-N,N'-dimethylcyclohexyldiamine catalyze the single-step C-O bond cross-coupling between 1,2-di- and trisubstituted vinylic halides with functionalized alcohols, producing acyclic vinylic ethers. This stereospecific transformation selectively gives each of the (E)- and (Z)-vinylic ether products from the corresponding vinyl halide precursors. This method is compatible with carbohydrate-derived primary and secondary alcohols and several other functional groups. The conditions are mild enough to reliably generate vinylic allylic ethers without promoting Claisen rearrangements.

A Tropomycin-Related Kinase B Receptor Activator for the Management of Ocular Blast-Induced Vision Loss

Pressure waves from explosions or other traumatic events can damage the neurons of the eye and visual centers of the brain, leading to functional loss of vision. There are currently few treatments for such injuries that can be deployed rapidly to mitigate damage. Brain-derived neurotrophic factor (BDNF) and activation of its receptor tropomycin-related kinase B (TrkB) have neuroprotective effects in a number of degeneration models. Small molecule activators of TrkB, such as N-[2-(5-hydroxy-1H-indol-3-yl)ethyl]-2-oxopiperidine-3-carboxamide (HIOC), cross the blood-brain and blood-retina barriers after systemic administration. We characterize the effects of blast-induced ocular trauma on retinal and visual function. We show that systemic administration of HIOC, a potent small molecule activator of the BDNF/TrkB receptor, preserves visual function in mice exposed to ocular blast injury. The HIOC treatment for one week preserves visual function for at least four months. The HIOC treatment effectively protected vision when the initial dose was administered up to 3 h after blast, but not if the initial treatment was delayed for 24 h. We provide evidence that the therapeutic effect of HIOC is mediated by activation of BDNF/TrkB receptors. The results indicate that HIOC may be useful for managing ocular blast injury and other forms of traumatic optic neuropathy.

Alkynylation of Pentose Derivatives with Stereochemical Fidelity: Implications for the Regioselectivity of Alkynyl Diol Cycloisomerizations to Cyclic Enol Ethers

This work characterizes a previously undetected epimerization in the preparation of alkynyl diols from pentose precursors utilizing the Ohira-Bestmann reagent. Lithium trimethylsilyldiazomethane (Colvin reagent) additions to the d-ribose and d-lyxose-derived benzylidene acetals provide the respective alkynyl diol stereoisomers, without epimerization. Regioselective tungsten-catalyzed cycloisomerizations of the d-ribose- and d-lyxose-derived alkynyl diols yield rigid bicyclic pyranose glycals, confirming the stereochemical fidelity of the Colvin alkynylation process.

Sequential exo-mode oxacyclizations for the synthesis of the CD substructure of brevenal

We describe a novel strategy for synthesizing the CD bicyclic ether substructure of the fused polycyclic ether natural product brevenal. This product arises from a three-step sequence beginning with (1) regio- and diastereoselective iodoetherification of an acyclic diene-diol, followed by (2) alkene metathesis with an epoxyalkene synthon, concluding with (3) palladium-catalyzed cycloisomerization. Despite the modest yield and long reaction period for the cycloisomerization step, these studies provide valuable insights into the nature of byproducts generated and the mechanisms by which they form. This work demonstrates a portion of a larger synthetic strategy for constructing the pentacyclic core of brevenal from an acyclic precursor.

Stereoselective Synthesis of Pyrans from Epoxyalkenes: Dual Catalysis with Palladium and Brønsted Acid

We describe regio- and stereoselective cycloisomerizations of alcohols tethered to epoxyalkenes, to construct alkene-substituted pyrans. These transformations are best catalyzed by Pd(PPh₃)₄ in the presence of phosphite ligands, and with diphenylphosphinic acid as an essential Brønsted acid cocatalyst for activation of the epoxyalkene.

Gram-scale, chemoselective synthesis of N-[2-(5-hydroxy-1H-indol-3-yl)ethyl]-2-oxopiperidine-3-carboxamide (HIOC)

N-[2-(5-hydroxy-1H-indol-3-yl)ethyl]-2-oxopiperidine-3-carboxamide (HIOC) is a potent activator of the TrkB receptor in mammalian neurons and of interest because of its potential therapeutic uses. In the absence of a commercial supply of HIOC, we sought to produce several grams of material. However, a synthesis of HIOC has never been published. Herein we report the preparation of HIOC by the chemoselective N-acylation of serotonin, without using blocking groups in the key acylation step.

Blockade of glioma proliferation through allosteric inhibition of JAK2

The gene that encodes the epidermal growth factor receptor (EGFR) is frequently overexpressed or mutated in human cancers, including glioblastoma. However, the efficacy of EGFR-targeted small-molecule inhibitors or monoclonal antibodies in glioblastomas that also have mutation or deletion of the gene encoding phosphatase and tensin homolog (PTEN) has been modest. We found that EGFR signaling was blocked by a small molecule (G5-7) that selectively inhibited Janus kinase 2 (JAK2)-mediated phosphorylation and activation of EGFR and STAT3 (signal transducer and activator of transcription 3) by binding to JAK2, thereby decreasing the activity of downstream signaling by mTOR (mammalian target of rapamycin) and inducing cell cycle arrest. G5-7 inhibited the proliferation of PTEN-deficient glioblastoma cell lines harboring a constitutively active variant of EGFR (U87MG/EGFRvIII) and human glioblastoma explant neurosphere cultures, but the drug only weakly inhibited the proliferation of either glioblastoma cell lines that were wild type for EGFR and stably transfected with PTEN (U87MG/PTEN) or normal neural progenitor cells and astrocytes. Additionally, G5-7 reduced vascular endothelial growth factor (VEGF) secretion and endothelial cell migration and induced apoptosis in glioblastoma xenografts, thereby suppressing glioblastoma growth in vivo. Furthermore, G5-7 was more potent than EGFR or JAK2 inhibitors that interfere with either ligand or adenosine 5'-triphosphate (ATP) binding at impeding glioblastoma cell proliferation, demonstrating that this allosteric JAK2 inhibitor may be an effective clinical strategy.

Abstract 5683: Blockade of glioma proliferation via allosteric inhibition of JAK2

Gliomas are the most common primary brain tumors. Glioblastoma multiforme (GBM), WHO grade IV, is the most frequent and aggressive form, with a median survival of approximately 12 months following aggressive treatment with surgical resection, radiation and chemotherapy. Epidermal growth factor receptor (EGFR) is frequently amplified and mutated in human cancers including GBM. While the rationale for treating GBM patients with EGR inhibitors is strong, the efficacy of anti-EGFR small molecular inhibitors or monoclonal antibodies in treating gliomas with PTEN mutation or deletion has been modest. Here we show a novel approach to inhibiting EGFR that involves a small molecule (G5-7) that selectively blocks JAK2 phosphorylation of EGFR, inhibits cell proliferation and reduces VEGF secretion, and leads to glioma shrinkage via apoptosis and anti-angiogenesis. G5-7 inhibited EGFR and STAT3 tyrosine phosphorylation by JAK2 through binding to its N-terminal FERM domain. Interestingly, G5-7 selectively inhibited the proliferation of U87MG/EGFRvIII cells and human GBM explant neurosphere cultures but only weakly affected U87MG/PTEN cells or normal neural progenitor cultures. Moreover, oral administration of this compound markedly diminishes the brain tumor volumes in both subcutaneous and intracranial models, supporting that this compound itself and/or the metabolites might be able to penetrate the brain-blood barrier and exert the anti-proliferative actions through blocking the oncogenic pathways in vivo. Chronic treatment of mice with 50 mg/kg G5-7 exhibits no obvious toxicity in the animals. Our finding demonstrates that G5-7 is a novel allosteric JAK2 inhibitor with potent anti-tumor activity for GBM. Our report not onlyidentify a novel drug for treating the GBM, but also provide insight into the molecular mechanisms of how these small molecules impinge on the EGFR/PTEN signaling. Optimization of these novel compounds will lead to new treatments for the patients with these devastating tumors.

[K.H. and Q.Q. contributed equally to this work.]

Citation Format: Kunyan He, Qi Qi, Chi-Bun Chan, Ge Xiao, Xia Liu, Carol Tucker-Burden, Liya Wang, Hui Mao, Xiang Lu, Frank E. McDonald, Hongbo Luo, Qi-wen Fan, William A. Weiss, Shi-yong Sun, Daniel J. Brat, Keqiang Ye. Blockade of glioma proliferation via allosteric inhibition of JAK2. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 5683. doi:10.1158/1538-7445.AM2013-5683

Brønsted acid-promoted glycosylations of disaccharide glycal substructures of the saccharomicins

An acid-promoted glycosylation and alkynol cycloisomerization sequence provided direct access to the 2-deoxytrisaccharide corresponding to the fucose-saccharosamine-digitoxose substructure of saccharomicin B. In the course of this work, the absolute stereochemistry of the repeating fucose-saccharosamine disaccharide of saccharomicins was also confirmed.

Stereo- and regioselective glycosylations to the bis-C-arylglycoside of kidamycin

In explorations toward the total synthesis of the antitumor anthrapyran natural product kidamycin, the regioselective introduction of aminosugars angolosamine and vancosamine as C-arylglycosides has been accomplished onto hydroxylated anthrapyran aglycones. Specifically, the 9,11-dihydroxylated anthrapyran A undergoes sequential glycosylations with angolosamine synthon B and vancosamine synthon C to regio- and stereoselectively afford bis-C-glycoside D corresponding to the C-glycoside pattern of kidamycin.

Fischer carbene catalysis of alkynol cycloisomerization: application to the synthesis of the altromycin B disaccharide

[reaction: see text] The tungsten-catalyzed cycloisomerization of alkynyl alcohols can be conducted without using photochemistry, using a stable tungsten Fischer carbene as the precatalyst for this transformation. A variety of alkynyl alcohols undergo cycloisomerization under these conditions to provide endocyclic enol ethers of five-, six-, and seven-membered ring sizes. The utility of this method is further demonstrated in the stereoselective synthesis of the disaccharide substructure of altromycin B.

Synthesis of 1-deoxysphingosine derivatives with conformationally restricted pyrrolidinediol head groups

[structure: see text] A family of cyclic 1-deoxysphingolipid derivatives of structure 4 has been designed and synthesized, which may serve as tumorigenesis suppressors for various cancers. Compound 4 is a second-generation analogue developed from sphingosine (1), in which a hydroxyl substituent is moved from C1 to C5 and a methylene is added for conformational rigidity between the C2-nitrogen substituent and C4. The synthetic chemistry for pyrrolidine ring closure at C3-C4 features ring-closing metathesis followed by hydroboration-oxidation.

Synthesis of the saccharomicin fucose-aglycon conjugate and determination of absolute configuration

[reaction: see text] Schmidt glycosylation of the appropriately protected 3,4-dihydroxycinnamate methyl ester with 2,3,4-triacetoxyfucopyranosyltrichloroacetimidate gives aryl glycoside in high yield and diastereoselectivity. 2-Sulfation of fucose, installation of taurine, and global deprotection of the remaining protecting groups affords the fucose-aglycon conjugate of saccharomicin. This synthesis which arises from L-fucose also establishes the absolute configuration of the reducing terminus of the saccharomicin oligosaccharide.

Synthesis of the aglycones of altromycins and kidamycin from a common intermediate

The aglycone structures 1 and 2, respectively corresponding to the antitumor antibiotic natural products altromycin and kidamycin, have been efficiently synthesized from a common advanced intermediate 3. A series of Claisen condensations and aromatizations affords the anthracene section of 3, followed by annulation of the pyrone ring. The functional groups of 3 can be manipulated for enantioselective introduction of the epoxide side-chain of altromycin aglycone 1, as well as synthesis of the kidamycin aglycone 2. [reaction: see text]

New chiral synthons for efficient introduction of bispropionates via stereospecific oxonia-cope rearrangements

Compounds 1 and 2 are novel synthons for bispropionate synthesis, undergoing stereospecific Lewis acid-catalyzed transfer of the bispropionate unit with a variety of aldehydes, including alpha-chiral aldehydes. Thus 1 leads to the E-alkene bispropionate 3 with anti-stereochemistry, whereas diastereomer 2 gives the Z-alkene product 4, under mild conditions and with complete stereospecificity. The efficacy of this methodology is demonstrated in a short synthesis of invictolide beginning with 2 and (R)-2-methylpentanal.

Alkene substituents for selective activation of endo-regioselective polyepoxide oxacyclizations

The presence of an alkenyl substituent on the terminal epoxide of a polyepoxide substrate enhances the yield of all-endo-regioselective tandem oxacyclization to trans-syn-trans-fused polycyclic ethers. For a substrate in which the epoxide and alkene functional groups are separated by two methylene substituents, a novel bromonium ion-induced endo-regioselective cyclization to bromooxepane is also described. [reaction: see text]

Synthesis of the branched C-glycoside substructure of altromycin B

Tungsten-catalyzed cycloisomerization of alkynyl alcohols including 8 provides only the endocyclic enol ether (11) as a key intermediate for the branched C-glycoside substructure (2) of altromycin B. A sequence of Stille cross-coupling reaction and regio- and stereoselective functional group transformations affords each C13-diastereomer of the branched C-arylglycoside (2a and 2b). [reaction: see text]

1-Deoxy-5-hydroxysphingolipids as New Anticancer Principles: An Efficient Procedure for Stereoselective Syntheses of 2-Amino-3,5-diols

[reaction: see text]. Enantioselective preparation of the linear homoallylic alcohol I allows efficient formation of the 2-amino-3,5-diol moiety present in several biologically active compounds, including 1-deoxy-5-hydroxysphingosine analogue IV, which has exhibited excellent biological activity against colon cancer. The conversion of I into IV involves a sequence of enantioselective epoxidation of the O-tert-butoxycarbonyl derivative of I, followed by regioselective and stereospecific oxacyclization of II to introduce differentiated oxygens in III.

Density Functional Study of Mo-Carbonyl-Catalyzed Alkynol Cycloisomerization: Comparison with W-Catalyzed Reaction

Mo-catalyzed endo-cycloisomerizations of alkynes tethered to alcohols have been studied using density functional theory, and comparisons were made with the W-catalyzed reaction. The cycloisomerization is initiated with the formation of metal alkyne pi complex and is followed by the rate-determining step, which transforms the pi complex to a vinylidene carbene complex, considered to be critical for endo-mode cyclization. Several different alkynols have been selected to investigate five- and six-membered ring endo-cycloisomerizations in the presence of Mo(CO)(5) catalyst. The energy barriers calculated for five- and six-membered ring cycloisomerizations are within a range of 25-30 kcal/mol for most cases studied, showing no significant energy difference between the two metals. The stabilization effect of THF and Et(3)N solvents and the substitution reaction of THF by alkynol substrates in the reaction process with Mo and W complexes are studied as well. The principal difference between Mo- and W-catalyzed cycloisomerization processes appears to be the initial formation of a pi complex, which is more stabilizing for formation of the W-alkyne vs Mo-alkyne complexes.

Biomimetic Synthesis of trans,syn,trans-Fused Polyoxepanes: Remarkable Substituent Effects on the endo-Regioselective Oxacyclization of Polyepoxides

The biogenesis of trans,syn,trans-fused polycyclic ether substructures of neurotoxic natural products of the brevetoxin-ciguatoxin family may involve regio- and stereoselective oxacyclizations of polyepoxides. We report that a biomimetic Lewis acid-promoted cyclization of 1 to 2 proceeds with endo-regioselectivity and anti-stereospecificity at each position of nucleophilic addition (C3, C7, C11, and C15 in 1) when the tandem cyclization cascade is terminated by a carbonyl oxygen nucleophile. In contrast to expectations from earlier reports with simpler epoxide substrates, alkyl substituents are not required at internal epoxide positions corresponding to C7 and C11 in polyepoxide 1. Furthermore, we report that trimethylsilyl serves as a removable regioselectivity-directing substituent at positions corresponding to C3 of 1. These results greatly expand the potential applications of this biomimetic oxacyclization cascade to the synthesis of fused polycyclic ether natural products.

Synthesis of Seven-Membered Ring Glycals via endo-Selective Alkynol Cycloisomerization

[reaction: see text] Alkynyldiols 1 undergo cycloisomerization to the corresponding seven-membered cyclic enol ethers 2 under tungsten carbonyl catalysis. This novel transformation proceeds with good yields and virtually complete regioselectivity for all diastereomers of 1, favoring the product 2 resulting from endo-mode cyclization. The unexpected regioselectivity may be dependent on the presence of the dioxolane structure tethering the terminal alkyne and diol functional groups.

Stereoselective Synthesis of d-Desosamine and Related Glycals via Tungsten-Catalyzed Alkynol Cycloisomerization

Stereoselective synthesis of d-desosamine diacetate ester (iii, R = Ac) was achieved from the glycal (ii). generated by tungsten carbonyl-catalyzed cycloisomerization of the corresponding amino-alkynol (i). A wide variety of N-substituents (R, R') are compatible with the cycloisomerization, provided that at least one R or R' is an acyl derivative.

Total synthesis of the polyene-polyol macrolide RK-397, featuring cross-couplings of alkynylepoxide modules

The total synthesis of the natural product RK-397 is based on a new synthetic strategy for assembling polyacetate structures, by efficient cross-coupling of nucleophilic terminal alkyne modules with electrophilic epoxides bearing another alkyne at the opposite terminus. The natural product is constructed from four principal modules: a polyene precursor for carbons 3-9, and three alkyne-terminated modules for carbons 10-16, 17-22, and 23-33. Each module is prepared with control of all stereochemical elements, and the alkynyl alcohols obtained from alkyne-epoxide couplings are converted into 1,3-diols by a sequence of hydroxyl-directed hydrosilylation, C-Si bond oxidation, and stereoselective ketone reduction with induction from the beta-hydroxyl group. The highly convergent nature of our synthetic pathway and the flexibility of the modular synthesis strategy for virtually any stereoisomer can provide access to other members of the polyene-polyol macrolides, including stereoisomers of RK-397.

Total Synthesis of the Polyene-Polyol Macrolide RK-397, Featuring Cross-Couplings of Alkynylepoxide Modules

The total synthesis of the natural product RK-397 is based on a new synthetic strategy for assembling polyacetate structures, by efficient cross-coupling of nucleophilic terminal alkyne modules with electrophilic epoxides bearing another alkyne at the opposite terminus. The natural product is constructed from four principal modules: a polyene precursor for carbons 3-9, and three alkyne-terminated modules for carbons 10-16, 17-22, and 23-33. Each module is prepared with control of all stereochemical elements, and the alkynyl alcohols obtained from alkyne-epoxide couplings are converted into 1,3-diols by a sequence of hydroxyl-directed hydrosilylation, C-Si bond oxidation, and stereoselective ketone reduction with induction from the beta-hydroxyl group. The highly convergent nature of our synthetic pathway and the flexibility of the modular synthesis strategy for virtually any stereoisomer can provide access to other members of the polyene-polyol macrolides, including stereoisomers of RK-397.

Organolanthanide-Catalyzed Intramolecular Hydroamination/Cyclization/Bicyclization of Sterically Encumbered Substrates. Scope, Selectivity, and Catalyst Thermal Stability for Amine-Tethered Unactivated 1,2-Disubstituted Alkenes

This paper reports the organolanthanide-catalyzed intramolecular hydroamination/cyclization of amine-tethered unactivated 1,2-disubstituted alkenes to afford the corresponding mono- and disubstituted pyrrolidines and piperidines using coordinatively unsaturated complexes of the type (eta(5)-Me(5)C(5))(2)LnCH(TMS)(2) (Ln = La, Sm), [Me(2)Si(eta(5)-Me(4)C(5))(2)]SmCH(TMS)(2), and [Me(2)Si(eta(5)-Me(4)C(5))((t)BuN)]LnE(TMS)(2) (Ln = Sm, Y, Yb, Lu; E = N, CH) as precatalysts. [Me(2)Si(eta(5)-Me(4)C(5))((t)BuN)]LnE(TMS)(2) mediates intramolecular hydroamination/cyclization of sterically demanding amino-olefins to afford disubstituted pyrrolidines in high diastereoselectivity (trans/cis = 16/1) and good to excellent yield. In addition, chiral C(1)-symmetric organolanthanide catalysts of the type [Me(2)Si(OHF)(CpR*)]LnN(TMS)(2) (OHF = eta(5)-octahydrofluorenyl; Cp = eta(5)-C(5)H(3); R* = (-)-menthyl; Ln = Sm, Y), and [Me(2)Si(eta(5)-Me(4)C(5))(CpR*)]SmN(TMS)(2) (Cp = eta(5)-H(3)C(5); R* = (-)-menthyl) mediate asymmetric intramolecular hydroamination/cyclization of amines bearing internal olefins and afford chiral 2-substituted piperidine and pyrrolidine in enantioselectivities as high as 84:16 er at 60 degrees C. The substrate of the structure NH(2)CH(2)CMe(2)CH(2)CH=CH(CH(2))(2)CH=CH(2) is regiospecifically bicyclized by [Me(2)Si(eta(5)-Me(4)C(5))((t)BuN)]LnE(TMS)(2) to the corresponding indolizidine skeleton in good yield and high diastereoselectivity. Thermolysis of (eta(5)-Me(5)C(5))(2)LaCH(TMS)(2) in cyclohexane-d(12) at 120 degrees C rapidly releases CH(2)(SiMe(3))(2) and leads to possible formation of fulvene (eta(6)-Me(4)C(5)CH(2)-) species. The thermolysis product readily reverts to active catalysts upon protonolysis by substrate and exhibits the same catalytic activity as the (eta(5),eta(1)-Me(5)C(5))(2)LaCH(TMS)(2) precatalyst at 120 degrees C in the cyclization of cis-2,2-dimethylhept-5-enylamine. Catalytically-active lanthanide-amido complexes (eta(5)-Me(5)C(5))(2)La(NHR)(NH(2)R)(n) and [Me(2)Si(eta(5)-Me(4)C(5))((t)BuN)]Sm(NHR)(NH(2)R)(n) are shown to be thermally robust species.

Biomimetic synthesis of fused polypyrans: oxacyclization stereo- and regioselectivity is a function of the nucleophile

[reaction: see text] The stereoselectivity of Lewis acid-induced endo-regioselective oxacyclizations of 1,4-diepoxides is dependent upon the nature of the terminating nucleophile. For instance, the tert-butyl carbonate-substituted diepoxide of 3,6-dimethylhepta-2,5-dien-1-ol provides a cis-fused bicyclic product, whereas the N,N-dimethylcarbamate derivative affords the trans-fused diastereomer. Stereospecific and regioselective conversion of the tertiary carbamate-terminated 1,4,7-triepoxide (I) to tricyclic all-trans-fused polypyran (II) is also demonstrated.

Stereoselective synthesis of L-oliose trisaccharide via iterative alkynol cycloisomerization and acid-catalyzed glycosylation

[formula: see text] The synthesis of an all-alpha L-oliose diastereomer of digitoxin provides valuable insights into the generality and protective-group dependence of acid-catalyzed glycosylations of glycals to 2-deoxycarbohydrates.

Stereoselective synthesis of a family of alternating polyols from six-carbon epoxyalkynol modules

Our new synthetic strategy for assembling polyacetate structures features efficient cross-couplings of six-carbon modules derived from any stereoisomer of the epoxyalkynol derivative (1). Hydration of the internal alkyne in the coupled products and stereoselective reduction of the resulting ketone intermediate provides a general approach to a library of stereoisomeric 1, 3, 5, ... alternating polyols (2). The strategy is demonstrated in a stereoselective synthesis of the C11-C28 polyol substructure of the natural product RK-397.

The prognostic influence of bcl-2 in malignant glioma

The bcl-2 gene is one of a complex group of genes which control programmed cell death. Bcl-2 acts to extend cell survival by blocking apoptosis, and thereby may influence tumour prognosis. This study of 187 high grade gliomas reviews clinicopathological prognostic features and the relationship to bcl-2 expression. Bcl-2 immunostaining was assessed in 159 specimens from these patients, by scoring systems of 0 to 3 for intensity of scoring and proportion of cells staining. Age, histology, pre- and post-operative performance status were found to be strongly predictive of survival (log rank test P<0.0001). The type of surgery performed did not influence survival in this group of patients. The expression of bcl-2 had a significant relationship with survival (univariate Cox model P=0.0302, hazard ratio 0.8, 95% confidence interval 0.65-0.98), with increased staining associated with improved survival. Multivariate analysis showed performance status, histology and proportion of cells staining for bcl-2 to be independently predictive of survival. Bcl-2 staining was not related to histological grade of tumours.