The syntheses, structure and reactivity of several boron derivatives of quinic acid, obtained in aprotic media, show that these boron heterocycles are useful intermediates, since they provide an alternative route to functionalize the quinic acid in a different way as when using dioxolane derivatives. Some new dioxolane derivatives of quinic acid and free quinide, as well as the lactone of quinic acid (61, were prepafed in very high yields. The conformations of all new compounds were established from H NMR measurements.
Introduction.
Many polyoxygenated carbocycles produce potent antimicrobial, antiviral and antitumoral responses, as well as growth-promoting effects'. Because of their pronounced biological activities and their potential as versatile chemical intermediates, polyoxygenated carbocycles have been the target of many synthetic effortsze4. Quinic acid (11, a very important natural polyhydroxylated cyclohexane, is an intermediate in the shikimate pathway to aromatic aminoacids5-7 and an important chiron in organic chemistry due to its four functionalized asymmetric carbons. Hence, it is relevant to investigate selective protection methods for these four hydroxy groups. We have been working with this molecule toward the total synthesis of enterocine213 and reported the characterization of a large number of derivatives 2,3,8 Interactions between boric acid and quinic acid have been studied by means of "B and 13C NMR only in aqueous solutionsg. In this paper we present our results for the preparation, in aprotic media, of some boron derivatives that could be relevant for the chemistry of quinic acid and of some other polyhydroxylated molecules. The new compounds were characterized by carbon-13, hydrogen-l and boron-11 NMR, as well as by 'H-'H and 13C-lH correlation spectra. From these experiments, their conformations were fully established.
Results and Discussion.
Phenylboronic
Derivatives.