Über enantiomerenreines (R)-2-Methyl-3-oxo-perhydro-1,4-oxazin

The synthesis of enantiomerically pure (R)-2-methyl-3-oxo-perhydro-1,4-oxazine is described for the first time. Stereochemical proofs are given and the formation of byproducts is discussed.

     

C-Glucuronides,a Novel Type of Drug Metabolites

The structure elucidation of C-β-glucuronides of sulfinpyrazone (Anturan^®) and phenylbutazone (Butazolidin^®) by spectroscopic means is reported. These conjugates represent a novel type of drug metabolites.     

A bicyclic cispentacin derivative as a novel reverse turn inducer in a GnRH mimetic

A cispentacin-derived bicyclic beta-amino acid (Bic) has been synthesized and incorporated into the 6-position of GnRH. The new GnRH analogue has been characterized with respect to its structure in solution and its activity and affinity toward the human GnRH receptor.     

A Sensitive and Selective High‐Throughput Screening Fluorescence Assay for Lipases and Esterases

Long‐chain fatty acid esters of 7‐(3,4‐dihydroxybutyloxy)‐2H‐1‐benzopyran‐2‐one ( 6 ) such as octanoate 2a are shown to be exceptionally sensitive and selective fluorogenic substrates for lipases and esterases. Umbelliferone ( 8 ) is released upon hydrolysis of the ester function in 2a in the presence of bovine serum albumin and sodium periodate. These substrates are at least by one order of magnitude more sensitive to lipases than the commercial fluorogenic substrate 4‐methylumbelliferyl heptanoate. Furthermore, they are stable to a broad range of pH‐induced‐ and thermal‐hydrolysis conditions and do not react with non‐catalytic proteins such as bovine serum albumin (BSA).     

Total synthesis of (-)-colchicine via a Rh-triggered cycloaddition cascade

[reaction: see text] A synthesis of the antimitotic alkaloids (-)-colchicine and (-)-isocolchicine is reported. Important steps are (a) enantioselective transfer-hydrogenation of an alkynone, (b) iodine/magnesium exchange with subsequent aromatic acylation, (c) Rh-catalyzed transformation of an alpha-diazoketone into an oxatetracyclic key intermediate through intramolecular [3 + 2]-cycloaddition of an in situ generated carbonyl ylide, and (d) regioselective conversion of the cycloadduct into a tropolone derivative. The new synthetic strategy opens an efficient enantioselective access to colchicine and structural analogues.     

Synthesis of ruthenium acetylides: new building blocks for molecular electronics

Several ruthenium(II) mono(acetylides) trans-[Cl(dppe)₂Ru---(CC)_n---R] (n=1–4; R=SiMe₃, H) and bis(acetylide) trans-[(dppe)₂Ru(---(CC)₂---R)₂] (R=SiMe₃, H) were selectively obtained and could be used as a new set of building blocks for rigid rod-like structures and further assemblies. Especially, the oxidative coupling of trans-[Cl(dppe)₂Ru---(CC)₃---H] with Cu(OAc)₂ led to the formation of the first Ruthenium(II) binuclear species with 12 carbon atoms between the remote metals. This compound shows two reversible redox processes.     

Diastereoselectivity and molecular recognition in the self-assembly of double-stranded dinuclear metal complexes of the type [M2[(R,S)-tetraphos]2](PF6)2 (M = Ag and Au)

The ligand (R,S)-Ph(2)PCH(2)CH(2)P(Ph)CH(2)CH(2)P(Ph)CH(2)CH(2)PPh(2), (R,S)-tetraphos, combines with silver(I) and gold(I) ions in the presence of hexafluorophosphate to diastereoselectively self-assemble the head-to-head (H,H) diastereomers of the double-stranded, dinuclear metal complexes [M(2)[(R,S)-tetraphos](2)](PF(6))(2) in which the two chiral metal centers in the complexes have M (R end of phosphine) and P (S end of phosphine) configurations. The crystal and molecular structures of the compounds have been determined: (H,H)-(M,P) -[Ag(2)[(R,S)-tetraphos](2)](PF(6))(2), monoclinic, P2(1)/c, a = 10.3784(2), b = 47.320(1), c = 17.3385(4) A, beta = 103.8963(5) degrees, Z = 4; (H,H)-(M,P)-[Au(2)[(R,S)-tetraphos](2)](PF(6))(2), monoclinic, P.2(1) (No. 4, c unique axis), a = 24.385(4), b = 46.175(3), c = 14.820(4) A, Z = 8. The complexes crystallize as racemic compounds in which the unit cell in each case contains equal numbers of enantiomorphic molecules of the cation and associated anions. The cations in both structures have similar side-by-side structures of idealized C(2) symmetry, the bulk helicity of each molecule in the solid state being due solely to the twist of the central ten-membered ring containing the two metal ions of opposite configuration, which has the chiral twist-boat-chair-boat conformation. When 1 equiv each of (R,S)-tetraphos, (R,R)-(+/-)-tetraphos, (S,S)-(+)-tetraphos, 2 equiv of Ph(2)PCH(2)CH(2)PPh(2) (dppe), and 7 equiv of [AuCl(SMe(2))] in dichloromethane are allowed to react for several minutes in the presence of an excess of ammonium hexafluorophosphate in water (two phases), the products are the double-stranded digold(I) complexes in which each ligand strand has recognized itself by stereoselective self-assembly, together with [Au(dppe)(2)]PF(6).