A chemical study of the bitter principle of pia (Tacca Leontopetaloides (L.) O. Ktze)

Typescript.Thesis (Ph. D.)--University of Hawaii, 1959.Bibliography: leaves 78-82.Pia belongs to the plant family Taccaceae, which consists of approximately thirty species (1), widely distributed over the warmer regions of the globe (2). Taccaceae contains only two genera, Schizocapsa and Tacca. The former consists of only two species located in the South China-Malaya area, while Tacca, which is sub-divided into three sections Ataccia, Palmotacca, and Eutacca - is more widely distributed (3). Limpricht (4) accepted the name Tacca pinnatifida J. & G. Forst. for pia, but the presently accepted name is Tacca Leontopetaloides (L.) O. Ktze (5)* Pia is probably native to tropical Asia and of aboriginal introduction to Hawaii (6), although the exact origin of this species is not known (7). Pia is an herb consisting of tuberous underground stems similar to the potato, with leaves that rise directly from the ground and which resemble papaya leaves. 'The stem, which may reach a height of four feet or more, is topped by a striking inflorescence of small green and purplish flowers (8) (see Fig. 1). The pia plant was cultivated for its starch content and was produced in Hawaii in sizable quantities in the 1850's for export to Europe under the name "arrowroot" (9). The plant is rarely cultivated now, but small quantities can still be found growing wild near Hilo in the Puna district. The pure starch from the pia tubers was combined with coconut cream, bananas or ti root juice to yield food staples eaten by most Polynesians. It was well known to the Hawaiians, however, that a bitter material had to be removed from the raw tuber in order to make the starch edible. The raw tuber has been reported to be toxic (10) and only the Easter Islanders are reputed to eat the unwashed tuber, but only after baking (11). The Hawaiians grated the tubers and washed them in running water for prolonged periods. The resultant bitter extract was used in this dilute state as a medicine to combat diarrhea and dysentery, particularly in infants (12). In 1857, Lepine carried out a superficial chemical analysis of pia and reported 2.2% of a bitter extract (13). This report is the sole published record of a chemical nature concerning pia. Except for a similar paper dealing with the bitterness and toxicity of Tacca umbrarum* (14), no chemical study has been made of any species of this plant family. Since no chemical compounds have been isolated from Taccaceae, a prediction of the general nature of the bitter principle cannot be made. It was hoped that a search of the literature for bitter principles from other plants might indicate some relationship from which the bitter principle of pia could be categorized as to type. Some representative bitter principles of current interest, some of which are still incompletely characterized, are listed in Table I. Only those containing carbon, hydrogen and oxygen are recorded, since they are more pertinent to this investigation, as will be seen later. It is apparent from Table I that non-nitrogenous bitter principles occur in widely diverse plant types - flowering plants and even lichens. Chemically, several skeletal types can be distinguished: steroid, terpenoid, aromatic and depsidone, any of which may be glycosidically bound to a sugar moiety. Although most of the compounds are highly oxygenated, the nature of the oxygen functions vary widely and any relationship which might exist is not immediately apparent. Due to this great diversity of chemical types found in plants, little ~ priori information can be surmised about the bitter principle of pia. It is interesting to note that many of these bitter principles possess pharmacological activity of great diversity. Because of the very small amount of the bitter principle that was obtained by extraction of the tubers, only a limited quantity was available for structural studies. Although micro methods were used, checking of results and duplicate runs frequently were impossible. The object of this investigation was to isolate, purify and characterize the bitter principle found in pia