2-Amino-1,3-dioxane, conformational

For compound 22, X-ray analysis demonstrates that the dioxane ring adopts the chair conformation and that the imidoyl amino group prefers an axial conformation <2002T2621>. For (l,4-benzodioxin-2(3//)-yl)methyl sulfamic acid ester 21, the conformation of the dihydrodioxin ring is close to an ideal half-chair and for 1,2,4,6,7,9-hexafluoro-... 

The second major metabolite from T. inflation is structurally closely related to cyclosporin A, as can be deduced by elemental analysis, mass spectrum (m/z 1217), IR and NMR spectra. Furthermore, the presence of the double bond and OH group of the unusual MeBmt was established. Sulphonic acids in methanol or dioxane effected the typical rearrangement reaction by N, O-acyl migration to the iso-compound (13). Hydrolysis furnished the same amino acids as cyclosporin A with the exception of L-a-aminobutyric acid, which is replaced in cyclosporin C (12) by L-threonine. The amino-acid sequence could be deduced by conversion of cyclosporin C into cyclosporin A via the corresponding tosylate (14) and iodo derivatives (15) [7]. Position 2 for L-threonine as well as the assumed twisted -pleated sheet conformation of the molecule were confirmed by 13C-NMR spectra. 

V,5S)-5-Amino-4-phenyl-2,2-dimethyl-l,3-dioxane and (4i ,5i )-5-amino-(4 -biphenyl)-2,2-dimethyl-1,3-dioxane were synthesized and employed as chiral solvating agents for the ee determination of compounds bearing an acidic proton by means of NMR spectroscopy (99TA323). Based on the rigid conformation of the two amines, they are... 

To demonstrate the versatility of his S3mthesis strategy Yamada used ketoester 151 as relais substance to S3mthesize two further picrotoxane alkaloids isolated from Dendrobium species, nobilonine (90) and 2-hydroxydendrobine (87) (Scheme 14) (84). Monobromination of 151 with bromine in dioxane and subsequent treatment with water resulted in hydroxy-y-lactam 152, whereas attempts to hydroxylate 151 by Barton oxidation led to rearrangements. Chemo- and stereoselective reduction with zinc borohydride converted 152 into the en fo-alcohol. To counterbalance the unfavorable conformational equilibrium this alcohol had to be converted into the alcoholate to achieve lactonization. Chemoselective reduction of the hydroxylac-tam moiety of lactone 153 again followed Borch s protocol, which led in this case to boron complexed amino compounds necessitating successive acid treatment to obtain racemic 2-hydroxydendrobine (87) in low yield accompanied by dendrobine (82). 2-Hydroxydendrobine (87) was converted into nobilonine (90) by Eschweiler-Clark methylation. 

Kirby AJ, Wothers PD (2001) Conformational equilibria involving 2-amino-1,3-dioxanes steric control of the anomeric effect. ARKIVOC XII 58-71... 

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