The dialkyl 2,6-dialkylsubstituted 4-piperidone-3,5-dicarboxylates were synthesized by a Mannich procedure. Depending on the substitution at the nitrogen keto-enol-tautomerism and a configurational isomerism at C 2 is observed. The structure o f the N-substituted piperidone 24 E (C 18H29N 0 5) has been determined by X-ray analysis: it is characterized by an enol structure o f the /?-ketoester a...

A new synthesis of (+)-gabosine C has been accomplished as part of a general diversity-oriented approach that also delivered the previously unknown (-)-4-epi-gabosine C. The identification of the unexpected intermediate (+)-8, together with the isolation of ketones 9 and 10 in previous investigations, prompted us to formulate a new hypothesis for the biosynthesis of gabosines, based on a keto-e...

One new drimane-type sesquiterpenoid, named ugandenial A (1), was isolated from the ethyl acetate extract of the bark of Warburgia ugandensis (Canellaceae) together with eight known drimane-type sesquiterpenoids: 11alpha-hydroxycinnamosmolide (2), warburganal (3), polygodial (4), mukaadial (5), dendocarbin A (6), 9alpha-hydroxycinnamolide (7), dendocarbin L (8) and dendocarbin M (9). Their stru...

We reinvestigated the assignment of the three major guanine conformers detected via resonance enhanced two-photon ionization (R2PI) in supersonic expansions and present IR/UV double resonance spectra in the spectral region between 1500 and 1800 cm(-1). Comparison with B3LYP/TZVPP and RI-MP2/cc-pVQZ calculations shows that both conformers B and C are 7H-keto tautomers with an imine group in the ...

The biosynthesis pathway to diadinoxanthin and fucoxanthin was elucidated in Phaeodactylum tricornutum by a combined approach involving metabolite analysis identification of gene function. For the initial steps leading to β-carotene, putative genes were selected from the genomic database and the function of several of them identified by genetic pathway complementation in Escherichia coli. They ...

Experimentally, it was observed that the oxidized guanine lesion spiroiminodihydantoin (Sp) contained in highly purified oligodeoxynucleotides slowly converts to guanidinohydantoin (Gh). The reaction is accelerated in the presence of acid. The possible mechanisms of this transformation have been analyzed computationally. Specifically, the potential energy surface for formation of Gh from Sp has...

We applied Horse Liver Alcohol Dehydrogenase (HLADH) to the enantioselective synthesis of six (2S)-2-arylpropanols, useful intermediates in the synthesis of Profens. The influence of substrate structure and reaction conditions on yields and enantioselectivity were investigated. The high yields and high enantioselectivity towards the (S)-enantiomer obtained in the bioreduction of 2-arylpropionic...

The anion of the title salt, C(6)H(9)N(2) (+)·C(6)H(4)NO(3) (-), undergoes an enol-to-keto tautomerism during the crystallization. In the crystal structure, the cation and anion are held together by a relatively short N-H⋯O hydrogen bond, and the two anions are further connected to each other by a pair of N-H⋯O hydrogen bonds with an R(2) (2)(8) ring motif, thus forming a centrosymmetric 2 + 2 ...