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Biomedical subjects

Robert M Adlington

Publications and source records attributed to Robert M Adlington.

At least 19 recordsLinked to original sources
PubMed2006

Unexpected oxidation of a depsipeptide substrate analogue in crystalline isopenicillin N synthase.

Isopenicillin N synthase (IPNS) is a non-heme iron(ii)-dependent oxidase that is central to penicillin biosynthesis. Herein, we report mechanistic studies of the IPNS reaction in the crystalline state, using the substrate analogue delta-(L-alpha-aminoadipoyl)-(3R)-methyl-L-cysteine D-alpha-hydroxyisovaleryl ester (AmCOV) to probe the early stages of the catalytic cycle. The X-ray crystal structure of the anaerobic IPNS:Fe(II):AmCOV complex was solved to 1.40 A resolution, and it reveals several subtle differences in the active site relative to the complex of the enzyme with its natural substrate. The crystalline IPNS:Fe(II):AmCOV complex was then exposed to oxygen gas at high pressure; this brought about reaction to give what appears to be a hydroxymethyl/ene-thiol product. A mechanism for this reaction is proposed. These results offer further insight into the delicate interplay of steric and electronic effects in the IPNS active site and the mechanistic intricacies of this remarkable enzyme.

Binding Sites↗
PubMed2005

Unique binding of a non-natural L,L,L-substrate by isopenicillin N synthase.

Isopenicillin N synthase (IPNS) is a non-haem iron oxidase that catalyses the formation of isopenicillin N from the tripeptide delta-(L-alpha-aminoadipoyl)-L-cysteinyl-D-valine. In this report, we describe the crystal structure of the enzyme with a non-natural L,L,L-tripeptide substrate, delta-(L-alpha-aminoadipoyl)-L-cysteinyl-L-3,3,3,3',3',3'-hexafluorovaline. This structure reveals a strong binding interaction of the tripeptide within the active site and a unique conformation for the non-natural L,L,L-diastereomer. Taken together, these findings provide a possible rationale for the previously observed inhibitory effects of L,L,L-tripeptide substrates on IPNS activity.

Binding Sites↗
PubMed2005

A new and efficient method for o-quinone methide intermediate generation: application to the biomimetic synthesis of the benzopyran derived natural products (+/-)-lucidene and (+/-)-alboatrin.

Lucidene and alboatrin are complex benzopyran derived natural products. A key step in their biogenesis may involve a hetero Diels-Alder cycloaddition between an o-quinone methide intermediate with a simple, or activated tri-substituted olefin. Experimental evidence is provided to support this hypothesis, with the biomimetic synthesis of both (+/-)-lucidene and (+/-)-alboatrin successfully achieved using a new and efficient method for o-quinone methide generation.

Alkenes↗
PubMed2005

A novel oxidative rearrangement of 6-methoxypyran-2-ones.

As part of our continuing studies of pyrone-containing natural products, a series 6-methoxypyran-2-ones were synthesized. These were found to react with molecular oxygen at 20 degrees C, and this novel reaction yielded a series of highly functionalized alpha,beta-butenolides. [reaction: see text]

Journal Article↗
PubMed2005

A short total synthesis of aureothin and N-acetylaureothamine.

The total synthesis of the nitrophenyl pyrones, (+/-)-aureothin and (+/-)-N-acetylaureothamine, starting from known 2-ethyl-6-methoxy-3,5-dimethyl-4H-pyran-4-one are described. The key steps involved in the synthesis are the construction of the tetrahydrofuran motif using a palladium-catalyzed cycloaddition and the ruthenium-catalyzed cross-metathesis reaction of an alkenyl boronic ester. [reaction: see text]

Acetylation↗
PubMed2005

Biomimetic total synthesis of (+)-himbacine.

On treatment with trifluoroacetic acid butenolide 14 undergoes N-Boc deprotection and condensation followed by an iminium ion activated intramolecular Diels-Alder cycloaddition to give the (+)-himbacine precursor 11 on reductive work up. Compound 11 was converted into (+)-himbacine in four synthetic steps. [reaction: see text]

4-Butyrolactone↗
PubMed2004

Dimerization of butenolide structures. A biomimetic approach to the dimeric sesquiterpene lactones (+/-)-biatractylolide and (+/-)-biepiasterolide.

The biomimetic synthesis of the bisesquiterpene lactones (+/-)-biatractylolide 1 and (+/-)-biepiasterolide 2 via dimerization of the captodative stabilized radical 8 is reported. Atractylon 7 has also been shown to be a possible intermediate during the biosynthesis of biatractylolide 1, biepiasterolide 2, atractylolide 3, and hydroxyatractylolide 4.

4-Butyrolactone↗
PubMed2003

Biomimetic studies on polyenes.

The crispatenes and SNF4435 C&D are complex polypropionate derived natural products. The core structures of these compounds along with a complex unnatural structure can be easily prepared from a common polyene precursor simply by variation of the reaction conditions. The reaction pathways provide insight into the biosynthesis of these complex natural products.

Magnetic Resonance Spectroscopy↗
PubMed2003

Total synthesis of panepophenanthrin.

[reaction: see text] The biomimetic synthesis of the racemic dimer panepophenanthrin was achieved in good yield employing a tandem reaction sequence.

Dimerization↗
PubMed2003

Crystallographic studies on the reaction of isopenicillin N synthase with an unsaturated substrate analogue.

Isopenicillin N synthase (IPNS) catalyses conversion of the linear tripeptide delta-(L-alpha-aminoadipoyl)-L-cysteinyl-D-valine (ACV) to isopenicillin N (IPN), the central step in biosynthesis of the beta-lactam antibiotics. The unsaturated substrate analogue delta-(L-alpha-aminoadipoyl)-L-cysteinyl-D-vinylglycine (ACvG) has previously been incubated with IPNS and single product was isolated, a 2-alpha-hydroxymethyl isopenicillin N (HMPen), formed via a monooxygenase mode of reactivity. ACvG has now been crystallised with IPNS and the structure of the anaerobic IPNS:Fe(II):ACvG complex determined to 1.15 A resolution. Furthermore, by exposing the anaerobically grown crystals to high-pressure oxygen gas, a structure corresponding to the bicyclic product HMPen has been obtained at 1.60 A resolution. In light of these and other IPNS structures, and recent developments with related dioxygenases, the [2 + 2] cycloaddition mechanism for HMPen formation from ACvG has been revised, and a stepwise radical mechanism is proposed. This revised mechanism remains consistent with the observed stereospecificity of the transformation, but fits better with apparent constraints on the coordination geometry around the active site iron atom.

Catalysis↗