Synthesis of Highly Condensed Polycyclic Carbohydrates by Reaction of a Spirocyclic Enamino Sulfonate Derived from d-Xylofuranose with Bifunctional Reagents

The appropriately substituted 5-O-tosyl derivative (1), easily prepared from 1,2-O-isopropylidene-α-d-xylofuranose, serves as a useful precursor for the preparation of highly condensed cyclic carbohydrates.
The synthesis involves a first cyclization of the 5-O-tosyl sugar derivative 1 to a highly reactive cyclic
enamine, which subsequently undergoes the nucleophilic attack of a bifunctional reagent X(CH2)nZ in a
regio- and stereospecific way. Finally, a spontaneous cyclization step allows the formation of a
stereochemically defined extra ring, fused to the sugar backbone. The functionalization and size of this
ring can be varied by the proper choice of the bifunctional reagent. X-ray diffraction analysis and intensive
NMR studies with one of these carbohydrates were performed to highlight the strained nature of these
compounds.

经适当取代的5-O-甲苯磺酰基衍生物（5-O-tosyl derivative）1可由1,2-O-异亚丙基-α-d-木呋喃糖（1,2-O-isopropylidene-α-d-xylofuranose）简便制备，是合成高度稠合环状碳水化合物的实用前驱体。
该合成路线首先将5-O-甲苯磺酰基糖衍生物1环化为高活性环状烯胺（cyclic enamine），随后该中间体以区域及立体专一性（regio- and stereospecific）方式，接受双官能团试剂（bifunctional reagent）X(CH₂)ₙZ的亲核进攻（nucleophilic attack）。最终通过自发环化步骤，可形成与糖骨架（sugar backbone）稠合的、立体化学构型明确的额外环。该环的官能化修饰与环尺寸可通过选用合适的双官能团试剂进行调控。
研究人员通过X射线衍射分析（X-ray diffraction analysis）与核磁共振（NMR）研究，对其中一种目标碳水化合物展开表征，以阐明此类化合物的环张力特性（strained nature）。