Tetracyclic diterpenoids with a new carbon skeleton forming products of the cyclization of labdane diterpenoids
From the product of the cyclization of a mixture of isomeric ent-copalols (i) [i] with a mixture of formic and concentrated acids, we have isolated an oxygen-containing fraction (yield 47%) consisting of a mixture of five alcohols and their formates. Three of the alcohols proved to be known: isoagath-12-en-15-ols epimeric at Cz4 [2] and 14~-hibanol [3]. For the other two alcohols, with the composition C2oH3~O, structures (2) and (3) were shown, these being based on a new carbon skeleton [4].
Cationic cyclization of bicyclic diterpenes
Manool and agathadiol cyclize in formic acid to the 13-epimeric pimara-8,15-dienes and 14α-hydroxyhibane derivatives. The mechanistic and biosynthetic implications of these results are discussed in relation to other work involving cations in tetracyclic diterpenes. The nuclear magnetic resonance spectra of relevant tricyclic and tetracyclic diterpenes are documented.
Archaeology and mud wall decay in a West African village
Abstract A detailed study of the processes of deterioration of mud walls and of the physical evolution and devolution of a contemporary West African village is seen to facilitate the location of decayed mud structures at a nearby archaeological site. Various climatic and pedological conditions at the site make it unlikely that such walls will be discerned. The archaeologist wishing to obtain the fullest and least biased picture of the settlement configuration of the ancient community should therefore heed all the inferential lessons to be had from a focused ethnographic investigation. Given similar climatic situations and practices of house construction, taphonomy and ethnographic analogies may both be necessary for a valid reconstruction of an archaeological settlement.