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Allenyl carbinols undergo regioselective hydrostannation in the presence of MoBl3, a catalyst originally developed for the hydrostannation of alkynes, giving rise to allyl stannanes. These allyl stannanes can easily be converted into useful synthetic building blocks such as allyl iodides or vinyl epoxides.

Endothiopeptides can easily be obtained via Ugi reaction using thio acids as acid components. If isonitriles with an acetal group are applied, the endothiopeptides can directly be converted into thiazoles using TMSCl-NaI under microwave irradiation.

Allenylcarbinols undergo regioselective hydrostannation in the presence of MoBl3, a catalyst which was developed for the hydrostannation of propargyl alcohols and derivatives; allylstannanes are formed preferentially, which can easily be converted into allyl iodides.

N- and C-terminal diallylated peptides are obtained by several approaches, such as peptide Claisen rearrangement, N- and O- allylation, and the Ugi reaction of allyl-protected components. These diallylated peptides are suitable substrates for ring-closing metathesis and the success of this cyclisation was investigated with respect to the ring size, the position of the allyl moieties and the reaction parameters. In general, excellent yields are obtained for cyclisation of allyl glycine subunits and N-allylated amides, while allyl esters and allyl carbamates often presented serious problems. However, yields of up to 73% were obtained under optimised conditions, and the new generated double bond is formed with excellent trans-selectivity.

Allylic carbonates 8 bearing an electron-withdrawing ester functionality can act as substrates for palladium-catalyzed allylic alkylations or as Michael acceptors with the option to undergo subsequent ring closure. Chelated amino acid ester enolates 1' are versatile nucleophiles for both reactions giving high yields and selectivites., (Copyright 2004 American Chemical Society)

THF/carbonyl complexes of molybdenum and tungsten are suitable precursors for the synthesis of the corresponding monoisonitrile carbonyl complexes. Whereas complexes with electron-rich isonitriles are suitable for regioselective hydrostannations, complexes with electron-poor isonitriles are efficient catalysts for distannations, without reduction of aromatic halides. This allows for the synthesis of halogenated distannylated allyl ethers, which can be subjected to intramoleculare Stille couplings giving rise to heterocycles, which can be further modified at the remaining stannyl group.

A simple approach to several cyclopeptidmimetics containing an N-alkylated amino acid was found via a multicomponent reaction followed by a ring-closing metathesis starting from readily available precursors. The combinatorial technique has the advantage that different polar, hydrophilic or hydrophobic moieties can be placed at any position in the cycles and unnatural amino acids can also be incorporated.

Several types of furanomycin analogues were synthesized and investigated with respect to their antibacterial activity. Two different synthetic pathways were developed, based on aldol reactions/ring closing metathesis and an ester enolate Claisen rearrangement. Only the natural product and its desmethyl derivative showed antibacterial activity, pointing towards a narrow structure-activity relationship.

Diastereomer ratios of up to 95:5 and enantiomeric excesses of up to 95% were achieved in Pd-catalyzed asymmetric alyllic substitutions with zinc enolates of glycine esters as nucleophiles; a remarkable effect of the ligand on the diastereoselectivity of the substitution was found.

Claisen rearrangements of glycine crotyl ester enolates in the presence of chelating metal salts and chiral ligands provide ,-unsaturated amino acids in a highly stereoselective fashion. Best results are obtained with electron withdrawing protecting groups, isopropylates of aluminum and magnesium, and the cinchona alkaloids as chiral ligands. While the use of quinine gives rise to the (2R)-configured amino acids, quinidine provides the opposite enantiomer. The different enantiomers can also be obtained by using only one of the chiral ligands by simply changing the reaction conditions. A mechanistic rational for the stereochemical outcome of the reaction is given, which is supported by several experiments.

Hydrostannations of propargylic glycine esters with the new hydrostannation catalyst [Mo(CO)3(CNtBu)3] (MoBI3) gave rise to alpha-stannylated allylic esters in good yield and with high regioselectivity. The chelate Claisen rearrangements of these esters allow the syntheses of gamma,delta-unsaturated amino acids with a vinylstannane moiety in the side chain. The amino acids obtained can be further modified by cross-coupling with various types of electrophiles.

Complementary to the Claisen rearrangement, the title reaction-which when carried out with chelated enolates of amino acid esters as nucleophiles gives rise to unsaturated amino acids-preferentially provides anti instead of syn products. This palladium-catalyzed reaction proceeds under very mild conditions and is suitable for the synthesis of enantiomerically pure amino acids (see reaction scheme). Tfa=trifluoroacetyl., (© 1999 WILEY-VCH Verlag GmbH, Weinheim, Fed. Rep. of Germany.)

A new cyclic octapeptide, cyclo(Ile-Ser-(Gly)Thz-Ile-Thr-(Gly)Thz) (PatN), related to patellamide A, has been synthesized and reacted with copper(II) and base to form mono- and dinuclear complexes. The coordination environments around copper(II) have been characterized by EPR spectroscopy. The solution structure of the thermodynamically most stable product, a purple dicopper(II) compound, has been examined by simulating weakly dipole-dipole coupled EPR spectra based upon structural parameters obtained from force field (MM and MD) calculations. The MM-EPR method produces a saddle-shaped structure for [Cu(2)(PatN)(OH(2))(6)] that is similar to the known solution structure of patellamide A and the known solid-state structure of [Cu(2)(AscidH(2))CO(3)(OH(2))(2)]. Compared with the latter, [Cu(2)(PatN)] has no carbonate bridge and a significantly flatter topology. The MM-EPR approach to solution-structure determination for paramagnetic metallopeptides may find wide applications to other metallopeptides and metalloproteins.

Ester enolate Claisen rearrangement of highly substituted amino acid allylic esters 4 allows for the synthesis of sterically demanding amino acids 5 with beta-quaternary carbon centers. Because of enolate fixation by chelation, the rearrangement occurs in a highly diastereoselective fashion. The methodology is suitable not only for glycine derivatives but also for allylic esters of various amino acids. In this case amino acids with two vicinal quaternary carbon centers are created. With unsymmetrically substituted allylic esters like 4k-n the rearrangement proceeds with a high degree of diastereoselectivity.