A Two-Dimensional NMR Study of Poly(vinyl (dialkylamino)alkylcarbamate-<i>co</i>-vinyl acetate-<i>co</i>-vinyl alcohol)

The microstructure of amine-modified poly(vinyl acetate-co-vinyl alcohol) (P(VAM−VOH−VAC)) copolymers was studied by a combination of 2D NMR techniques COSY (correlated spectroscopy), 1H−13C HMQC (heteronuclear multiple-quantum correlation), and HMBC (heteronuclear multiple-bond correlation). A complete signal assignment was achieved on a representative sample poly(vinyl 3-(dimethylamino)propylcarbamate-co-vinyl acetate-co-vinyl alcohol). The microstructures of the poly(vinyl alcohol) (PVA) backbone and the amine substitution are thus determined. The correct assignment of methylene peaks in the 1H spectrum of previously reported PVA was verified on the basis of COSY spectra. Tacticities obtained from the methine 13C signals reveal that mainly isotactic triads react with the activated diamine. By using the 1H−13C HMBC technique, the covalent bond between PVA backbone and amine was clearly confirmed. Furthermore, the tacticity assignment of pure PVA could be substantiated by the HMBC spectra

Coupling of <i>cyclo</i>-l‑Trp‑l‑Trp with Hypoxanthine Increases the Structure Diversity of Guanitrypmycins

The cyclo-l-Trp-l-Trp (cWW, 1) tailoring P450 GutD2774 from Streptomyces lavendulae was characterized by expression in Streptomyces coelicolor, precursor feeding and enzyme assays. GutD2774 catalyzes mainly the transfer of hypoxanthine to C2 and C3 of the indole ring of 1. cWW adducts with guanine were detected as minor products. An orthologous cluster was identified in Streptomyces xanthophaeus. These results expand the spectrum of cyclodipeptide derivatives by involvement of an additional nucleobase and identification of new coupling patterns

Breaking Cyclic Dipeptide Prenyltransferase Regioselectivity by Unnatural Alkyl Donors

The behavior of five cyclic dipeptide prenyltransferases, responsible for C2-regular, C2-reverse, or C3-reverse prenylation, was investigated in the presence of the unnatural alkyl donors monomethylallyl and 2-pentenyl diphosphate. Both substrates were well accepted by the tested enzymes. Interestingly, C2-reverse and C3-reverse monoalkylated derivatives were identified as enzyme products in all of the enzyme assays. These findings indicate their similar reaction characteristics in the presence of unnatural alkyl donors

K–H₃C and K–Sn Interactions in Potassium Trimethylstannyl Complexes: A Structural, Mechanochemical, and NMR Study

A series of trimethylstannyl potassium complexes [K­(L)­SnMe₃] with different auxiliary ligands L (L = 18-C-6, (TMEDA)₂ (TMEDA = tetramethylethylenediamine), and (12-C-4)₂) were synthesized by alkoxide-induced B–Sn bond cleavage. X-ray structure determinations were performed for all these complexes, and the structural chemistry was studied in detail. For L = 18-C-6 and (TMEDA)₂ the solid state structures comprise polymeric [K­(L)­SnMe₃]_<i>n</i> chains containing bidentate trimethylstannyl anions bridging two [K­(L)]⁺ ions, featuring unsymmetrical coordination of the [K­(L)]⁺ ion by K–Sn and K–H₃C interactions as a central structural motif. In contrast, for L = (12-C-4)₂, separated [K­(12-C-4)₂]⁺ and [SnMe₃]⁻ ions are observed. Unexpectedly, in the presence of tetrahydrofuran (THF), [K­(18-C-6)­SnMe₃]_<i>n</i> forms upon crystallization a new species consisting of separated [K­(18-C-6)­(THF)₂]⁺ and [(Me₂SnCH₃)­K­(18-C-6)­SnMe₃]⁻ ions. In this unsymmetrical anion two trimethylstannyl anions coordinate a single [K­(18-C-6)]⁺ ion; one trimethylstannyl anion coordinates via a K–Sn interaction, and the second coordinates via a K–H₃C interaction. Simulations of the mechanochemical properties (compliance constants) applying approximated density functional theory revealed that both interactions are very soft and are of comparable strength. Moreover, according to our gas phase simulations the unsymmetrically coordinated [(Me₂SnCH₃)­K­(18-C-6)­SnMe₃]⁻ is indeed thermodynamically favored over both possible symmetrical isomers with either K–Sn or K–H₃C coordination. Furthermore, the existence of multiple species due to the two coordination modes and aggregates of [K­(18-C-6)­SnMe₃] in solution is suggested by NMR spectroscopic studies using ¹H, NOESY/ROESY, and ¹H pulsed field gradient diffusion experiments

Expansion of Enzymatic Friedel–Crafts Alkylation on Indoles: Acceptance of Unnatural β‑Unsaturated Allyl Diphospates by Dimethylallyl-tryptophan Synthases

Prenyltransferases of the dimethylallyl-tryptophan synthase (DMATS) superfamily catalyze Friedel–Crafts alkylation with high flexibility for aromatic substrates, but the high specificity for dimethylallyl diphosphate (DMAPP) prohibits their application as biocatalysts. We demonstrate here that at least one methyl group in DMAPP can be deleted or shifted to the δ-position. For acceptance by some DMATS enzymes, however, a double bond must be situated at the β-position. Furthermore, the alkylation position of an analogue can differ from that of DMAPP

Strategy for the Stereochemical Assignment of Tris-Heteroleptic Ru(II) Complexes by NMR Spectroscopy

The relative stereochemistry of tris-heteroleptic ruthenium complexes [Ru(pp)(pp′)(pp′′)](PF6)2, where pp = 1,10-phenanthroline-4-carboxamide, pp′ = 5,6-dimethyl-1,10-phenanthroline, and pp′′ = 7,8-dimethyl dipyrido[3,2-a:2′,3′-c]phenazine, was studied using NMR spectroscopy. The 1H and 13C spectra were assigned by using double-quantum-filtered correlation spectroscopy (DQF-COSY), heteronuclear single-quantum correlation (HSQC), and heteronuclear multiple-bond correlation (HMBC) experiments for the two diastereomers, each a pair of enantiomers. Nuclear Overhauser effect contacts between the neighboring ligands differentiated the two halves of each symmetrical ligand, thus enabling a full assignment of the NMR signals and an accurate determination of the relative stereochemistry of the complexes. The introduction of an additional chiral center to ligand pp by coupling it with l-lysine caused removal of the enantiomerism. Thus, four diastereomers were observed and their relative stereochemistry determined

K–H₃C and K–Sn Interactions in Potassium Trimethylstannyl Complexes: A Structural, Mechanochemical, and NMR Study

A series of trimethylstannyl potassium complexes [K­(L)­SnMe₃] with different auxiliary ligands L (L = 18-C-6, (TMEDA)₂ (TMEDA = tetramethylethylenediamine), and (12-C-4)₂) were synthesized by alkoxide-induced B–Sn bond cleavage. X-ray structure determinations were performed for all these complexes, and the structural chemistry was studied in detail. For L = 18-C-6 and (TMEDA)₂ the solid state structures comprise polymeric [K­(L)­SnMe₃]_<i>n</i> chains containing bidentate trimethylstannyl anions bridging two [K­(L)]⁺ ions, featuring unsymmetrical coordination of the [K­(L)]⁺ ion by K–Sn and K–H₃C interactions as a central structural motif. In contrast, for L = (12-C-4)₂, separated [K­(12-C-4)₂]⁺ and [SnMe₃]⁻ ions are observed. Unexpectedly, in the presence of tetrahydrofuran (THF), [K­(18-C-6)­SnMe₃]_<i>n</i> forms upon crystallization a new species consisting of separated [K­(18-C-6)­(THF)₂]⁺ and [(Me₂SnCH₃)­K­(18-C-6)­SnMe₃]⁻ ions. In this unsymmetrical anion two trimethylstannyl anions coordinate a single [K­(18-C-6)]⁺ ion; one trimethylstannyl anion coordinates via a K–Sn interaction, and the second coordinates via a K–H₃C interaction. Simulations of the mechanochemical properties (compliance constants) applying approximated density functional theory revealed that both interactions are very soft and are of comparable strength. Moreover, according to our gas phase simulations the unsymmetrically coordinated [(Me₂SnCH₃)­K­(18-C-6)­SnMe₃]⁻ is indeed thermodynamically favored over both possible symmetrical isomers with either K–Sn or K–H₃C coordination. Furthermore, the existence of multiple species due to the two coordination modes and aggregates of [K­(18-C-6)­SnMe₃] in solution is suggested by NMR spectroscopic studies using ¹H, NOESY/ROESY, and ¹H pulsed field gradient diffusion experiments

Coupling of Guanine with <i>cyclo</i>-l‑Trp‑l‑Trp Mediated by a Cytochrome P450 Homologue from <i>Streptomyces purpureus</i>

A cyclo-l-Trp-l-Trp tailoring P450 with novel function from <i>Streptomyces purpureus</i> was identified by heterologous expression in <i>S. coelicolor</i> and in vitro assays the recombinant protein. Structural elucidation revealed that this enzyme catalyzes the transfer of a guanine moiety to the indole ring of the cyclodipeptide via a C–N bond. Adduct products of CDP and guanine are unprecedented in nature, and CDP modification by coupling with guanine has not been reported prior to this study

Synthesis and Characterization of a <i>N,C,N</i>-Carbodiphosphorane Pincer Ligand and Its Complexes

The reaction of 2-pyridiyldiphenylphosphine (2) with tetrachloromethane and subsequent dehalogenation of the intermediate chloro phosphonium salt [(CDPPy2)­Cl]Cl (3) with tris­(1-pyrrolidyl)­phosphine results in the formation of a new type of carbodiphosphorane N,C,N pincer ligand, sym-bis­(2-pyridyl)­tetraphenylcarbodiphosphorane, CDPPy2 (1). It crystallizes in a triclinic crystal system with a crystallographic point group of P1̅. This neutral double-ylidic N,C,N ligand is capable of stabilizing a wide range of metal coordination polyhedra, varying from square planar [(CDPPy2)­PdCl]Cl (4), octahedral mer-[(CDPPy2)­TiCl3] (5) and fac-[(CDPPy2)­Cr­(CO)3] (6) to trigonal-bipyramidal [(CDPPy2)­MnCl2] (9) and [(CDPPy2)­CoCl2] (10) complexes. Unprecedented dinuclear complexes are formed with molybdenum and nickel carbonyls. 1 reacts with [Mo­(CO)3(NCMe)3] to form the symmetric κ3-N,C,N-[(CDPPy2)­Mo­(CO)3(μ-CO)­Mo­(CO)3] (7) with one bridging carbonyl next to a bridging central carbon atom with its two lone pairs. In contrast, an unsymmetrical coordination mode with only one coordinated pyridine is observed in κ2-N,C-[(CDPPy2)­Ni­(CO)­(μ-CO)­Ni­(CO)2] (8). Carbodiphosphorane-based ligands are unique due to their σ,π four-electron-donor character of the central carbon atom toward one metal and alternatively their 2σ four-electron-donor character toward two vicinal metal atoms

Synthesis and Characterization of a <i>N,C,N</i>-Carbodiphosphorane Pincer Ligand and Its Complexes

The reaction of 2-pyridiyldiphenylphosphine (2) with tetrachloromethane and subsequent dehalogenation of the intermediate chloro phosphonium salt [(CDPPy2)­Cl]Cl (3) with tris­(1-pyrrolidyl)­phosphine results in the formation of a new type of carbodiphosphorane N,C,N pincer ligand, sym-bis­(2-pyridyl)­tetraphenylcarbodiphosphorane, CDPPy2 (1). It crystallizes in a triclinic crystal system with a crystallographic point group of P1̅. This neutral double-ylidic N,C,N ligand is capable of stabilizing a wide range of metal coordination polyhedra, varying from square planar [(CDPPy2)­PdCl]Cl (4), octahedral mer-[(CDPPy2)­TiCl3] (5) and fac-[(CDPPy2)­Cr­(CO)3] (6) to trigonal-bipyramidal [(CDPPy2)­MnCl2] (9) and [(CDPPy2)­CoCl2] (10) complexes. Unprecedented dinuclear complexes are formed with molybdenum and nickel carbonyls. 1 reacts with [Mo­(CO)3(NCMe)3] to form the symmetric κ3-N,C,N-[(CDPPy2)­Mo­(CO)3(μ-CO)­Mo­(CO)3] (7) with one bridging carbonyl next to a bridging central carbon atom with its two lone pairs. In contrast, an unsymmetrical coordination mode with only one coordinated pyridine is observed in κ2-N,C-[(CDPPy2)­Ni­(CO)­(μ-CO)­Ni­(CO)2] (8). Carbodiphosphorane-based ligands are unique due to their σ,π four-electron-donor character of the central carbon atom toward one metal and alternatively their 2σ four-electron-donor character toward two vicinal metal atoms