Assignment of the Absolute Configuration of (+)-Diplopyrone, the Main Phytotoxin Produced by Diplodia mutila, the Pathogen of the Cork Oak Decline, by a Non Empirical Analysis of its Chiroptical Properties

The nonempirical assignment of the abs. configuration of (+)-diplopyrone, the main phytotoxin of D. mutila, i.e., an endophytic fungus, widespread in Sardinian oak forests, and considered one of the main causes of cork oak decline, has been approached by 2 different methods: (a) the exciton anal. of the CD spectrum and (b) the ab initio calcn. of the optical rotatory power. Both methods indicate that (+)-diplopyrone is 6-[(1S)-1-hydroxyethyl]-2,4a(S),6(R),8a(S)-tetrahydropyrano[3,2-b]pyran-2-one, so the stereostructure of this important biomol. is safely detd. for the 1st time. A comparison of advantages and limitations of the 2 methods of anal. is also presented.