Safety and efficacy of immunotherapy with the recombinant B-cell epitope-based grass pollen vaccine BM32.

BACKGROUND: BM32 is a grass pollen allergy vaccine based on recombinant fusion proteins consisting of nonallergenic peptides from the IgE-binding sites of the 4 major grass pollen allergens and the hepatitis B preS protein. OBJECTIVE: We sought to study the safety and clinical efficacy of immunotherapy (allergen immunotherapy) with BM32 in patients with grass pollen-induced rhinitis and controlled asthma. METHODS: A double-blind, placebo-controlled, multicenter allergen immunotherapy field study was conducted for 2 grass pollen seasons. After a baseline season, subjects (n = 181) were randomized and received 3 preseasonal injections of either placebo (n = 58) or a low dose (80 µg, n = 60) or high dose (160 µg, n = 63) of BM32 in year 1, respectively, followed by a booster injection in autumn. In the second year, all actively treated subjects received 3 preseasonal injections of the BM32 low dose, and placebo-treated subjects continued with placebo. Clinical efficacy was assessed by using combined symptom medication scores, visual analog scales, Rhinoconjunctivitis Quality of Life Questionnaires, and asthma symptom scores. Adverse events were graded according to the European Academy of Allergy and Clinical Immunology. Allergen-specific antibodies were determined by using ELISA, ImmunoCAP, and ImmunoCAP ISAC. RESULTS: Although statistical significance regarding the primary end point was not reached, BM32-treated subjects, when compared with placebo-treated subjects, showed an improvement regarding symptom medication, visual analog scale, Rhinoconjunctivitis Quality of Life Questionnaire, and asthma symptom scores in both treatment years. This was accompanied by an induction of allergen-specific IgG without induction of allergen-specific IgE and a reduction in the seasonally induced increase in allergen-specific IgE levels in year 2. In the first year, more grade 2 reactions were observed in the active (n = 6) versus placebo (n = 1) groups, whereas there was almost no difference in the second year. CONCLUSIONS: Injections of BM32 induced allergen-specific IgG, improved clinical symptoms of seasonal grass pollen allergy, and were well tolerated.

Advances in Phosphasilene Chemistry.

Heavier alkene analogues possess unique electronic properties and reactivity, encouraging multidisciplinary research groups to utilize them in the rational design of novel classes of compounds and materials. Phosphasilenes are heavier imine analogues, containing highly reactive Si=P double bonds. Recent achievements in this field are closely related to the progress in the chemistry of stable low-coordinate silicon compounds. In this Review, we have attempted to summarize in a comprehensive way the available data on the structures, syntheses, electronic and chemical properties of these compounds, with an emphasis on recent achievements.

Systematic Study of N-Heterocyclic Carbene Coordinate Hydrosilylene Transition-Metal Complexes.

An in-depth study of the synthesis and structures of N-heterocyclic carbene (NHC)-stabilized silylene transition-metal complexes is reported. An iron hydrosilylene complex, [tBu3Si(NHC)(H)Si:→Fe(CO)4] (2), was synthesized starting from the corresponding hydrosilylene [tBu3Si(NHC)(H)Si:] (1). Complex 2 was fully characterized, including X-ray diffraction analysis, which showed an unusual long Si-Fe bond length. A very long bond length was also observed in the novel hydrosilylene tungsten complex [tBu3Si(NHC)(H)Si:→W(CO)5] (3). A series of NHC-stabilized silylene iron complexes ([R2(NHC)Si:→Fe(CO)4], where R = Cl (4), H (5), and Me (6)) were synthesized and fully characterized to investigate the influence of different substituents. The dihydrosilylene iron complex [H2(NHC)Si:→Fe(CO)4] (5) represents a new example of a donor-acceptor-stabilized parent silylene (H2Si:). Density functional theory calculations were utilized to understand the influence of the electronic and steric effects of the silylene unit and its substituents on the Si-Fe bond in these iron complexes, in particular to rationalize the long Si-Fe bond in 2.

Reaction of an N-heterocyclic carbene-stabilized silicon(II) monohydride with alkynes: [2+2+1] cycloaddition versus hydrogen abstraction.

An in depth study of the reactivity of an N-heterocyclic carbene (NHC)-stabilized silylene monohydride with alkynes is reported. The reaction of silylene monohydride 1, tBu3 Si(H)Si←NHC, with diphenylacetylene afforded silole 2, tBu3 Si(H)Si(C4 Ph4 ). The density functional theory (DFT) calculations for the reaction mechanism of the [2+2+1] cycloaddition revealed that the NHC played a major part stabilizing zwitterionic transition states and intermediates to assist the cyclization pathway. A significantly different outcome was observed, when silylene monohydride 1 was treated with phenylacetylene, which gave rise to supersilyl substituted 1-alkenyl-1-alkynylsilane 3, tBu3 Si(H)Si(CHCHPh)(CCPh). Mechanistic investigations using an isotope labelling technique and DFT calculations suggest that this reaction occurs through a similar zwitterionic intermediate and subsequent hydrogen abstraction from a second molecule of phenylacetylene.

New route to access an acyl-functionalized phosphasilene and a four-membered Si-P-C-O heterocycle.

An acyl-functionalized phosphasilene, LSi(COtBu)=P(SiMe3) (L = PhC(NtBu)2) was synthesized on a new route by the addition of tBuCOCl to the phosphinosilylene LSiP(SiMe3)2 and subsequent Me3SiCl elimination. DFT studies elucidated its molecular structure, the influence of the acyl group on UV/Vis transitions, and revealed the mechanism. The intermediate LSi(COtBu)ClP(SiMe3)2, with a five-coordinate silicon center, was characterized by NMR spectroscopy and X-ray analysis. On the other hand, phosphasilene LSi(SiMe3)=P(SiMe3) reacted with tBuCOCl by a [2+2] cycloaddition of the silicon-phosphorus double bond and the carbon-oxygen double bond in addition to Me3SiCl elimination, thereby affording the novel, fully characterized compound LSi(SiMe3)[P=C(tBu)O] bearing a Si-P-C-O heterocycle with a phosphorus-carbon double bond. DFT studies suggest that two mechanisms occur simultaneously.

From a zwitterionic phosphasilene to base stabilized silyliumylidene-phosphide and bis(silylene) complexes.

The reactivity of ylide-like phosphasilene 1 [LSi(TMS)═P(TMS), L = PhC(NtBu)2] with group 10 d(10) transition metals is reported. For the first time, a reaction of a phosphasilene with a transition metal that actually involves the silicon-phosphorus double bond was found. In the reaction of 1 with ethylene bis(triphenylphosphine) platinum(0), a complete silicon-phosphorus bond breakage occurs, yielding the unprecedented dinuclear platinum complex 3 [LSi{Pt(PPh3)}2P(TMS)2]. Spectroscopic, structural, and theoretical analysis of complex 3 revealed the cationic silylene (silyliumylidene) character of the silicon unit in complex 3. Similarly, formation of the analogous dinuclear palladium complex 4 [LSi{Pd(PPh3)}2P(TMS)2] from tetrakis(triphenylphosphine) palladium(0) was observed. On the other hand, in the case of bis(cyclooctadiene) nickel(0) as starting material, a distinctively different product, the bis(silylene) nickel complex 5 [{(LSi)2P(TMS)}Ni(COD)], was obtained. Complex 5 was fully characterized including X-ray diffraction analysis. Density functional theory calculations of the reaction mechanisms showed that the migration of the TMS group in the case of platinum and palladium was induced by the oxidative addition of the transition metal into the silicon-silicon bond. The respective platinum intermediate 2 [LSi{Pt(TMS)(PPh3)}P(TMS)] was also experimentally observed. This is contrasted by the reaction of nickel, in which the equilibrium of phosphasilene 1 and the phosphinosilylene 6 [LSiP(TMS)2] was utilized for a better coordination of the silicon(II) moiety in comparison with phosphorus to the transition metal center.

Cyclic and linear polyferrocenes with silicon and tin as alternating bridges.

The synthesis and characterization of ferrocene-based oligomers that contained two different elements (Si and Sn) as alternating bridges is described for the first time. The salt-metathesis reaction of R(2) Si[(C(5) H(4) )Fe(C(5) H(4) Li)](2) (R=Me, Et) with R'(2) SnCl(2) (R'=Me, nBu, tBu) afforded a mixture of oligomers (6(Me) SnMe(2), 6(Et) SnMe(2), 6(Me) SnnBu(2), 6(Et) SnnBu(2), 6(Me) SntBu(2), and 6(Et) SntBu(2)). These oligomers were characterized by (1) H, (13) C, (29) Si, and (119) Sn NMR spectroscopy and by mass spectrometry. MS (MALDI-TOF) studies of 6(Et) SnMe(2) revealed the presence of linear (l) and cyclic (c) species that contained up to 20 ferrocene moieties. The molecular weights of the polymers were determined by gel-permeation chromatography (GPC) and by dynamic-light scattering (DLS). GPC analysis revealed average molecular weights of 2100-6300 Da with respect to polystyrene as a standard. DLS analysis yielded very similar results. Some compounds, c-(6(Me) SnMe(2) )(1), c-(6(Me) SntBu(2))(2), c-(6(Et) SnMe(2))(1), c-(6(Et) SntBu(2))(2), l-(6(Me) SnnBu(2) )(2), and l-(6(Me) SnnBu(2))(3), which contained up to six ferrocene moieties, were isolated in their pure form either by column chromatography or by crystallization. The Si- and Sn-bridged macrocycles that contained four ferrocene units (c-(6(Me) SntBu(2))(2) and c-(6(Et) SntBu(2))(2)) were structurally characterized by single-crystal X-ray analysis.

[1.1]Ferrocenophanes and bis(ferrocenyl) species with aluminum and gallium as bridging elements: synthesis, characterization, and electrochemical studies.

Salt-metathesis reactions between dilithioferrocene (Li(2)fc·2/3tmeda) and intramolecularly coordinated aluminum and gallium species RECl(2) [R = 5-Me(3)Si-2-(Me(2)NCH(2))C(6)H(3); E = Al (2a), Ga (2b); and R = (2-C(5)H(4)N)Me(2)SiCH(2); E = Al (3a), Ga (3b)] gave respective [1.1]ferrocenophanes ([1.1]FCPs). Those obtained from 2a and 2b, respectively, were isolated as analytically pure compounds and fully characterized including single-crystal X-ray structure determinations [4a (Al): 43%; 4b (Ga): 47%]. Bis(ferrocenyl) compounds of the type REFc(2) [R = 5-Me(3)Si-2-(Me(2)NCH(2))C(6)H(3); E = Al (5a), Ga (5b); and R = (2-C(5)H(4)N)Me(2)SiCH(2); E = Al (6a), Ga (6b)] and R(2)SiFc(2) [R = Me (7(Me)); Et (7(Et))] were prepared, starting from respective element dichlorides and lithioferrocene (LiFc). Molecular structures of 6a, 7(Me), and 7(Et) were solved by single-crystal X-ray analyses. One of the two Fc moieties of 6a was bent toward the open coordination site of the aluminum atom. The measured dip angles α* of the two independent molecules in the asymmetric unit were 11.9(5) and 13.3(5)°, respectively. The redox behavior of [1.1]FCPs 4 and bis(ferrocenyl) species 5, 6, 7, and (Mamx)EFc(2) [Mamx = 2,4-tBu(2)-6-(Me(2)NCH(2))C(6)H(2); E = Al (8a), Ga (8b)] were investigated with cyclic voltammetry. While all gallium and silicon compounds gave meaningful and interpretable data, all aluminum compounds were problematic with the exception of 8a. Aluminum species, compared to respective gallium species, are more sensitive and, presumably, fluoride ions or residual water from the electrolyte and solvent are causing degradation. The splitting between the formal potentials for bis(ferrocenyl) species was significantly smaller (5b, 6b, and 8b: ΔE°' = 0.138-0.159 V) than that of the [1.1]FCP 4b (ΔE°' = 0.309 V). These results were explained by assuming an electrostatic interaction between the two iron centers; differences between bis(ferrocenyl) species and [1.1]FCPs are likely due to a more effective solvation of Fe-containing moieties in the more flexible bis(ferrocenyl) species.

Phosphinosilylenes as a novel ligand system for heterobimetallic complexes.

A dihydrophosphinosilylene iron complex [LSi{Fe(CO)4}PH2] has been prepared and utilized in the synthesis of novel heterobimetallic complexes. The phosphine moiety in this phosphinosilylene complex allows coordination towards tungsten leading to the iron-tungsten heterobimetallic complex [LSi{Fe(CO)4}PH2{W(CO)5}]. In contrast, the reaction of [LSi{Fe(CO)4}PH2] with ethylenebis(triphenylphosphine)platinum(0) results in the formation of the iron-platinum heterobimetallic complex [LSi{Fe(CO)4}PH{PtH(PPh3)2}] via oxidative addition.

Facile rotation around a silicon-phosphorus double bond enabled through coordination to tungsten.

Unprecedented E/Z isomerisation of a Si[double bond, length as m-dash]P bond was observed by temperature dependent NMR spectroscopy. DFT calculations showed that the coordination of phosphasilene to tungsten lowered the rotational barrier from 19.1 to 14.2 kcal mol(-1). The thermodynamically more stable phosphinosilylene tungsten complex is formed at elevated temperatures through substituent migration.

Correction: Facile rotation around a silicon-phosphorus double bond enabled through coordination to tungsten.

Correction for 'Facile rotation around a silicon-phosphorus double bond enabled through coordination to tungsten' by Nora C. Breit et al., Chem. Commun., 2015, DOI: 10.1039/c5cc04247j.

Ferrocenophanes with gallium and silicon as alternating bridges.

[1.1]Ferrocenophanes with gallium and silicon in bridging positions have been prepared in yields of 29 and 41%, respectively. From the same reactions, polymer-containing fractions were isolated (31% in each case) and shown to be comprised of linear and cyclic species with up to 16 ferrocene units (MALDI-TOF analysis).