Baccatin-I11 (3), -1V (4, -VI (7), and the l-dehydroxy derivative of baccatin-IV are taxane derivatives with an oxetan ring.RECENTLY taxol (1),1 a natural product with potent antileukemic and tumour inhibiting properties, was shown to be a taxane derivative with an oxetan ring. This ring system in natural products is rare. One other taxane derivative containing it is baccatin-V (2) .2 p3The structures of further oxetan-containing taxanes have now been determined. They are baccatin-IV4 (5), C,,H,-014, m.p. 254-255" (decomp.), [ a ] D + 19O, Amax 219nm, E 5000 ; 1-dehydroxybaccatin-IV (6) , C,,H,,O,,, m.p. 286" (decomp.), [a],, + 5O, Amax 218 nm, E 7000; baccatin-IV (7), 274, and 282 nm, E 17,600, 860, and 640; and baccatin-VII (8), C36H5,0,4, m.p. 270" (decomp.), [a]= + go, hmax 218 nm, E 2500. C,,H,~O,*J "*p* 244-245" (decomp.)~ [ a ] ~ -5') Amax 225,

No abstract

Baccatin-V, C3,H3,01,, a new diterpenoid from Taxus baccata L. has been shown by X-ray analysis to contain an oxetan ring and to be 5@,20-epoxy-l@,2a,4a,-7a, log, 13~-hexahydroxytax-1 1-en-9-one 4a, 1 OP-diacetate 2cc-benzoate (I).

NUMBER 21/1970 I 1 NOVEMBER The Structure of the Diterpenoid Baccatin-I, the 4P,2O-Epoxide of 2 a,5 a,7P,9a,l OP,l3a-HexaU acetoxytaxa-4(2 0),11 -diene

The signs of the Cotton Effects associated with each of the mono-olefinic centres in taxane derivatives can be used to assign the absolute configuration of the molecule. THE. Octant Rule for chiral mono-olefinsl? relates the absolute configuration of a variety of endo-and exo-cyclic alkenes to the sign of the lowest energy Cotton Effect.3 The olefinic centres in the taxane skeleton provide examples of both rigid trans-cyclodecene and exo-methylene geometry in a highly oxygenated environment. Moreover, the T +T* olefinic U.V. absorption normally found between 190 and 200 nm is displaced to higher wavelengths (210-230 nm) in the bicyclo [5,3,l]undecane ~e r i e s . ~ It was therefore of interest to apply octant analysis to the 0.r.d. and c.d. spectra (Table ; Figures 1 and 2) of the taxanes (I)-(XCI) *4--6 R1 R2 R3 R4 R5 Re H OAc