Ulrich Burger

nolO and noeI (HsnIII) of Rhizobium sp. NGR234 are involved in 3-O-carbamoylation and 2-O-methylation of Nod factors.

Loci unique to specific rhizobia direct the adjunction of special groups to the core lipo-oligosaccharide Nod factors. Host-specificity ofnodulation (Hsn) genes are thus essential for interaction with certain legumes. Rhizobium sp. NGR234, which can nodulate >110 genera of legumes, possesses three hsn loci and secretes a large family of Nod factors carrying specific substituents. Among them are 3-O (or 4-O)- and 6-O-carbamoyl groups, an N-methyl group, and a 2-O-methylfucose residue which may bear either 3-O-sulfate or 4-O (and 3-O)-acetyl substituents. The hsnIII locus comprises a nodbox promoter followed by the genes nodABCIJnolOnoeI. Complementation and mutation analyses show that the disruption of any one of nodIJ, nolO, or noeI has no effect on nodulation. Conjugation of nolO intoRhizobium fredii extends the host range of the recipient to the non-hosts Calopogonium caeruleum and Lablab purpureus, however. Chemical analyses of the Nod factors produced by the NodI, NolO, and NoeI mutants show that the nolO andnoeI gene products are required for 3 (or 4)-O-carbamoylation of the nonreducing terminus and for 2-O-methylation of the fucosyl group, respectively. Confirmation that NolO is a carbamoyltransferase was obtained from analysis of the Nod factors produced by R. frediicontaining nolO; all are carbamoylated at O-3 (or O-4) on the nonreducing terminus. Since mutation of both nolO andnodU fails to completely abolish production of monocarbamoylated NodNGR factors, it is clear that a third carbamoyltransferase must exist. Nevertheless, the specificities of the two known enzymes are clearly different. NodU is only able to transfer carbamate to O-6 while NolO is specific for O-3 (or O-4) of NodNGR factors.

Formation of peptide impurities in polyester matrices during implant manufacturing

Most peptides are susceptible, in vivo, to proteolytic degradation, and it is difficult to formulate and to deliver them without loss of biological activity. In addition, it is often desirable to release them continuously and at a controlled rate over a period of weeks or months. For these reasons, a controlled release system is suitable. Poly(lactic acid) (PLA) is a biocompatible and biodegradable material that can be used for many applications, including the design of injectable controlled release systems for pharmaceutical agents. Development of these delivery systems presents challenges in the assessment of stability, specially for peptide drugs. By means of an extrusion method, long-acting poly(lactic acid) implants containing vapreotide, a somatostatin analogue, were prepared. The nature of the main degradation product obtained after implant manufacturing was elucidated. It was found that the main peptide impurity was a lactoyl lactyl-vapreotide conjugate. Because lactide are found in small quantities in most commercially available PLA, the influence of residual lactide in the polymeric matrix, on the formation of peptide impurities during manufacturing, was specially investigated. This work demonstrates that the degree of purity of the carrier is of great importance with regard to the formation of peptide impurities.

The cyanide catalyzed isomerization of enol esters derived from cyclic 1,3-diketones

Cross-over experiments unveil that the mechanism of the title reaction consists in cleavage of enol esters by cyanide with transient formation of acyl cyanides. These react as ‘soft’ C-acylating agents with the enolates freed in the initial step. Use is made of the acyl cyanide derived from pyrrole-2-carboxylic acid to set up the triketide type skeleton 12 of the antibiotic pyoluteorin 16. The aromatization of 12 with mercuric acetate gave the pyrrolo[a]indolone 18.

Epiartemisinin, a remarkably poor antimalarial: implications for the mode of action.

Epiartemisinin (7) was prepared by the base epimerization of artemisinin (1) and its structure determined by X‐ray analysis. The antimalarial activity of 7 against the chloroquine‐sensitive and resistant strains of Plasmodium berghei and P. yoelii in the mouse was compared with that of the highly effective schizonticide 1 and found to be drastically diminished. It is argued that the mode of action on the intraerythrocytic parasite by 7 is compromised by steric hindrance arising from the α‐disposed Me group. In the initial step, intimate complexation with heme is hindered or biased to favor the formation of a less potent C‐centered radical, the final lethal agent.

An iridoid diester from Valeriana officinalis var. sambucifolia hairy roots

A new iridoid diester (1R,2S,6S,9S)-5-acetyloxymethyl-9-methyl-3-oxabicyclo[4.3.0.]non-4-en-2-yl isovalerate), which we have named valdiate, was isolated from the hairy roots of Valeriana officinalis var. sambucifolia Mikan transformed with Agrobacterium rhizogenes R1601. It was characterized by its chemical and physical data. Together with valdiate, five valepotriates were isolated and identified by means of mass spectrometry and 1H and 13C NMR spectrometry. The analysis of the non-transformed plant roots belonging to the same species, indicated the absence of valdiate and the presence of four valepotriates only.

Dérivés C-glycosyliques : Partie XI. Étude de la chloration d'oximes d'aldéhydo-sucres☆

Abstract The chlorination of oximes of aldehydo sugars takes place via an S E 2′ mechanism and gives the corresponding gem -chloronitroso derivatives which are in equilibrium with their dimers. The study of the monomer formation from the dimer by n.m.r. spectroscopy at various temperatures indicates a positive difference of standard entropy. The gem -chloronitroso derivatives obtained isomerize into hydroximoyl chlorides.

The Photohydration of N-Glycosylpyridinium Salts and of Related Pyridinium N,O-Acetals

The photolysis of N-MEM-pyridinium chloride (1e) in alkaline H2O gave N-MEM-6-azabicyclo[3.1.0]hexenol (2e). With benzoic acid in CHCl3, this bridged aziridine gave a complex aminal 7 reminiscent by its C2 symmetry of Trogers base. Photolysis of α-d-glucopyranosyl pyridinium chloride (α-12) gave a 1:1 mixture of the corresponding α-d-glucopyranosyl aziridines (α-13/α-14), which were separated, after peracetylation, by crystallisation. The absolute configuration of one of the bridged aziridines (α-16) was established by X-ray analysis.

Sym-benzvaleno-benzo-benzvalene, a double valence isomer of anthracene

Abstract Dilithio-s-indacene ( 1 ) on reaction with excess chlorocarbene produces s-benzvaleno-benzo-benzvalene ( 3 ). Unlike benzvalene, it does not aromatize on heating but decomposes stepwise to 1,5- and 1,7-bis-methylene-dihydro-indacene ( 6 and 7 ).

[6π+4π] Cycloadditions of 5-azoniafulvene ions with nitrones and azomethine imines

Abstract Nitrones as well as azomethine imines generated by the prototropic route from hydrazones are shown to add readily to the title iminium ions to give pyrrolo-annellated oxadiazine and triazine derivatives.

Photochemical and thermal rearrangements of a benzoylnaphthobarrelene-like system

Abstract 8-Benzoyl-9-deuterionaphtho[de-2.3.4]bicyclo[3.2.2]nona-2,6,8-triene (12a)rearranges in a photochemical di-π-methane-type process to the l-benzoylatho[de-[2.3.4]tricyclo[4.3.0.02,9]nona-3,7-dienes 14a-c.The dihydro derivate 13a and the hydroxypheoylmethyl analogs 21a and 22a undergo similarly regioselective rearrangements to 15a+c, 23a-c, and 24a, respectively. At 298 K the primary photoreaction directly occus from the S1(n,π*) and T2(n,π*) states, and it proceeds from T1(π,π*) and from S2(π,π*) either directly or via T2. At lower temperature on direct irradiation. S1→T intersystem crossing and triplet reaction compete with reaction from the singlet. The rearrangement 12a→14a-c proceeds along three reaction paths evolving from the two primary photochemical processes of naphthyl-vinyl and vinyl-vinyl bonding in β-position to the CO (12→25+29). Two ground-state triplet diradical intermediates such as 25 and 27 have been shown to intervene consecutively—for the first time in di-π-methane photochemistry. Each has been characterized by ESR and IR, and the second one additionally by fluorescence and fluorescence excitation, and by laser flash photolysis. The failure of products 14a-c to interconvert photochemically is ascribed to efficient energy dissipation through thermally reversible pbotocleavage of the 3-membered ring. Compounds 12 and 14 thermally interconvert in the dark which constitutes the first example of a ground-state counterpart of a di-π-methane photorearrangement. The thermal reaction includes a path with highly regioselective (and possibly concerted) product formation competing with a stepwise process causing positional scrambling. The sequence 12→14 (photochemically; Φ = 1.0 at 366 nm and 298 K) and an electrophile-catalyzed reversal 14→12 in the dark is a model of a chemical light energy storage cycle which can be conducted without loss of reactants.