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Contribution of the anomeric effect to the solution and crystal structure of [1S,2S,6S,7S]-1,6-diaza-4,9-dioxa-2,7-dimethoxycarbonylbicyclo[4.4.1]und ecane, a condensation product of L-serine methyl ester with formaldehyde

Author:
Selambarom, J  Monge, S  Carre, F  Fruchier, A  Rogue, JP  Pavia, AA  


Journal:
CARBOHYDRATE RESEARCH


Issue Date:
2001


Abstract(summary):

The reaction of L-serine methyl ester hydrochloride (1) with paraformaldehyde (2) in dichloromethane in the presence of triethylamine afforded a novel compound: [1S,2S,6S,7S]-1,6-diaza-4,9-dioxa-2,7-dimethoxycarbonylbicyclo [4.4.1]undecane (4) as a 2:3 adduct of 1 with 2. H-1 and C-13 NMR spectroscopy were unable to discriminate between two possible symmetrical structures. The latter was unambiguously proved by X-ray crystallography. The crystal structure established: (i) the existence of two identical seven-membered rings each containing a N-C-O grouping; (ii) the existence of a long C-O-C-N-C-N-C-O-C sequence in which each nitrogen belongs simultaneously to a N-C-O (oxazolidine) and to a N-C-N (aminal) motifs; (iii) the existence of a chair-like conformation for both seven-membered rings; (iv) the antiperiplanar geometry of pN-C-O and consequently the manifestation of a strong anomeric effect in both N-C-O groupings, whereas anomeric effect was virtually absent in the N-C-N sequence, as corroborated by bond distances and bond angles. Chemical shifts, coupling constants and NOE effects confirm that the conformational features of 4 are preserved in solution. (C) 2001 Elsevier Science Ltd. All rights reserved.


Page:
43---51


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