Structural Characterization of Polyprenols

Polyisoprenoid alcohols consisting of 9 to 20 isoprene units have a widespread occurrence as indicated by their presence in the leaves of higher plants, mammalian tissues, and microorganisms. Most of the polyprenols isolated from higher plants consist of trans and ois isoprene units with the exception of solanesol, which is composed of all-trans isoprene units. The arrangement of trans and ois units in these polyprenols has been determined from a consideration of the mechanism of the formation of betula-prenols, C(30)-C(45), isolated from wood tissue of Betuta verrucosa (9). However, up to the present there has been no direct evidence to prove the location of the internal trans and ois units. 

The arrangement of the trans and ois units in typical polyprenols was determined according to information obtained from the 13C NMR study of acyclic terpenes mentioned above. Poly-prenol-11 C(55), isolated from the leaves of Fious elastioa was found to contain the t )-terminal unit, three internal trans units, six internal ois units, and a ois a-terminal unit from IH NMR observations. Polyprenol-12 C(60), isolated from Fious elastioa and silkworm feces, showed a similar composition except that there were seven internal ois units. 

These signals showed value of less than 1 s and nearly full NOE values. 

On the basis of these findings, it is concluded that polyprenols ll and 12 are composed of the w-terminal, three internal trans, six or seven internal cis, and cis a-terminal units aligned in that order as shown below  

This alignment of the trans and cis units clearly indicates that these polyprenols are synthesized vn vivo by the cis addition of isopentenyl pyrophosphate to trans,trans,trans-geranylgerany1 pyrophosphate (10). 

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This paper describes the structural analysis of naturally occurring ois-1,4 polyisoprenes using 13C NMR spectroscopy. First, the structural characterization of polyprenols, which are linear isoprenoid compounds containing 30 to 100 carbons, was carried out on the basis of information obtained from acyclic terpenes having various ois and trans isoprene units as model compounds. This method was also applied to the structural analysis of polyisoprenes. The elucidation of the structure of the end groups and the arrangement of isoprene units provides information on the mechanism of the biosynthesis of polyprenyl compounds in nature. 

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