The leaves of rose-bay willow-herb (Chamaenerion angustifolium) are shown to contain ursolic acid, oleanolic acid, maslinic acid, and a hitherto unknown acid, 2a-hydroxyursolic acid. A partial synthesis of the new acid is described and some of its derivatives are compared with the corresponding derivatives of the isomeric maslinic acid.* The compound described by Aplin and co-workers as 2-hydroxyursolic acid (see ref. 6b) was later shown to be maslinic acid.

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The Ipecacuanha alkaloids have structures based upon the C9-lo unit (I) which is ubiquitous in the indole group of alkaloids. Four theories have been proposed to account for the biosynthesis of this unit. One makes use of an aromatic C,-C, residue together with one or two one-carbon units. A second theory constructs the Csl0 system from three acetate units, a one-carbon unit, and a malonic acid residue. Strong evidence against both theories has been obtained by tracer experiments on the biosynthesis of cephaeline (11; R = H) in Cephaelis ipecacuanha; these experiments have further revealed the origin of the two isoquinoline systems in this alkaloid.This is discussed, using as a basis the results from tracer experiments which point against the involvement of a one-carbon unit in the genesis of the C9-10 system. The combined evidence indicates that further tracer studies are required to test rigorously the fourth published theory, based upon terpenoid precursors, and also the possibility that the Csl0 unit is derived from carbohydrate nietabolisni in a way not yet considered.The third theory involves rearrangement of prephenic acid.THE structure and the illustrated absolute stereochemistryl of emetine (11; R = Me) have been established by many degradative studies 2 and the results have been confirmed by several syntheses .3 Accompanying emetine in Cephaelis ipecacztanha is its phenolic relative, cephaeline (11; R = H), which can often be the major base present in the plants.These alkaloids and their close relatives are the only cases in the isoquinoline series to possess the C,-,, unit shown dissected in formula (I). This structural unit, as such or in apparently rearranged state, forms the reduced portion of the highly diverse structures found in the indole group of alkaloids. Corynantheine (111) serves as an example where the unit (I) can clearly be seen, and here the absolute stereochemistry corresponds to that of emetine.* In the Yohimbe, Aspidosperma, and Iboga alkaloids the C,-,, unit appears as (IV), (V), and (VI), respectively. The origin of this unit, is, at the time of writing, still one of the major unsolved problems in alkaloid biosynthesis, and several biogenetic schemes have been proposed to account for it ; these will be considered below. Because of the structural relation of the Ipecacuanha and the indole alkaloids, biosynthetic information derived from the one assists research on the other. Both types of alkaloid have been studied by tracer methods in our Laboratory during the past five years and the present Paper reports the results derived for emetine and cephaeline. Preliminary accounts of part of this work have been p~blished.~*6

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