Synthesis of highly condensed heterocycles using radical reactions

Using radical chemistry novel highly condensed heterocycles have been synthesized. The mechanism for their formation is discussed.     

Crystallization of Arthrobacter sp. strain 1C N-(1-D-carboxyethyl)-L-norvaline dehydrogenase and its complex with NAD+

The novel NAD+-linked opine dehydrogenase from a soil isolate Arthrobacter sp. strain 1C belongs to an enzyme superfamily whose members exhibit quite diverse substrate specificites. Crystals of this opine dehydrogenase, obtained in the presence or absence of co-factor and substrates, have been shown to diffract to beyond 1.8 ? resolution. X-ray precession photographs have established that the crystals belong to space group P21212, with cell parameters a = 104.9, b = 80.0, c = 45.5 ? and a single subunit in the asymmetric unit. The elucidation of the three-dimensional structure of this enzyme will provide a structural framework for this novel class of dehydrogenases to enable a comparison to be made with other enzyme families and also as the basis for mutagenesis experiments directed towards the production of natural and synthetic opine-type compounds containing two chiral centres.     

Total synthesis of himandravine

[reaction: see text] The first total synthesis of (+)-himandravine (1) is described, starting from (2S,6S)-cis-2-formyl-6-methyl-N-Boc-piperidine (8) in 11 linear steps and 17% overall yield. The key step involves a highly diastereoselective intramolecular Diels-Alder reaction of the key intermediate 5 that contains the entire latent carbon framework and functional group substitution of himandravine.     

Asymmetric synthesis of 4,4-disubstituted-2-imidazoli-dinones: potent NK1 antagonists

[structure: see text] A highly efficient and practical synthesis of 4,4-Disubstituted-2-Imidazolidinones utilizing a "self-reproduction of the center of chirality" strategy is described.     

A convenient synthesis of cis and trans 4-tert-butoxycarbonyl-substituted cyclohexylglycine

A novel synthesis of cis and trans substituted 4-tert-butoxycarbonyl cyclohexylglycines via asymmetric aminohydroxylation of vinyl styrene followed by reduction of the aromatic ring and subsequent oxidation is reported.     

Application of ruthenium-induced macrocyclization for the construction of macrocyclic depsipeptides

The synthesis of a biaryl ether containing macrocyclic depsipeptide 1 was achieved in 6% overall yield. The desired macrocycle was constructed by cyclization of a phenol into eta(6)-ruthenium complex. The ruthenium metal was subsequently photolytically deprotected to obtain the macrocycle 1.     

Backbone rearrangements of methyl (-)-kaur-9(11)-en-19-oate and its epoxide: structures of two diterpenes of a new skeletal type

cleavage of the epoxide ($\text{2}$) of methyl (-)-kaur-9(11)-en-19-oate ($\text{1b}$) with boron trifluoride-ether in benzene and in acetic anhydride yielded ($\text{3a}$) and ($\text{3b}$), respectively. On epoxidation with $\text{m}$-chloroperbenzoic acid in the presence of $\text{N}$-nitrosomethyl urea, ($\text{1b}$) suffered a backbone rearrangement to form ($\text{6}$).     

Predictive schemes for the reactivity of borane carbonyl and the stability of carbonyltrihydroborate anions, BH3C(O)X

The reactivity of borane carbonyl (BH₃CO) and its isoelectronic counterpart the acetylium cation (CH₃CO⁺) are compared resulting in the formulation of (carbonyl)trihydroborate anions, BH₃C(O)X⁻, which are isoelectronic and isostructural with organic carbonyls. By analogy with the ease of reduction of organic carbonyl compounds by hydroborate, the relative stability towards self-reduction-oxidation (hydride transfer from boron to carbonyl carbon) in BH₃C(O)X⁻ is proposed. The postulated order, with increasing stability is BH₃C(O)Cl⁻ < BH₃C(O)H⁻ < BH₃C(O)R⁻ < BH₃C(O)OR⁻ < BH₃C(O)NR⁻₂ < BH₃C(O)O²⁻. Experimental results of this study together with known chemistry are shown to be consistent with the proposed order. Further, it is suggested that a similar predictive scheme may be applicable to the chemistry of the amine-carboxyboranes (boron analogues of -amino acids) and their derivatives.