Kawa Constituents — Hansel 
305 
saponified and methanol split off only with diffi- 
culty in the case of kawain? We may reduce this 
question to that of the alkali stability of the enol 
ethers of the two homologous acids (see formu- 
las) . 
C 6 H 5 — CH = CH — C(R) = 
CH — C(OCH 3 ) t= CH— COoH 
OH- 
R = H (kawaic acid) > no methanol 
OH- 
R = OH (yangona acid) > methanol 
Spectroscopic Characterization of the Kawa 
Lactones 
So far in this paper we have seen that the 
characteristic constituents of kawa are substi- 
tuted 6-membered lactones which may be classi- 
fied into two main groups, with one or two 
double bonds in the ring, the enolides and the 
dienolides. We have seen further that these two 
main types may be distinguished by their be- 
havior during alkaline hydrolysis. In the follow- 
ing section we will show that recognition of the 
hydrogenation type is achieved more quickly 
and more smoothly with the modern methods 
of IR, UV, and mass spectrometry. 
IR spectra (Hansel, Rimpler, and Lang- 
hammer, 1966) : It is best to start with two 
simple model compounds, the methyl-triacetyl 
acid lactone and the dihydromethyltriacetyl acid 
lactone (DH-MTL), which we prepared for 
the first time. The IR spectra of these two model 
compounds are exceedingly clear in the region of 
carbon-carbon double bond frequencies. DH- 
MTL exhibits in this region a single strong band 
at 1622 cm -1 which accordingly has to be as- 
signed to the enolic double bond at A 3 - In MTL 
this band — probably because of conjugation of 
the two carbon-carbon double bonds — is shifted 
toward longer wave numbers by 26 cm' 1 . We 
therefore assign the band at 1566 cm -1 to the 
double bond at A 5 - The assignment of one 
of the two hydrogenation types is also possible 
when the lactone rings are substituted by styryl 
or phenylethyl radicals. The band at 955-966 
cm' 1 , which shows a trans CHR = CHR link- 
age, is well suited for the determination whether 
we are dealing with a styryl or a phenylethyl 
type. We dealt with a total of four hydrogena- 
tion types for which we were able to develop 
a simple infrared assignment scheme as shown 
in Figure 10. The relationships are simplified 
and numerous details are omitted. 
mass spectra of the kawa lactones (Pailer 
et al., 1965) : Compounds of the yangonin type 
(Fig. 11) are best discussed first. We are deal- 
ing here with a conjugated system. There is no 
point in the molecule which facilitates the for- 
mation of energetically favorable fragments. 
We therefore find in this type of compound 
large molecular ions and little fragmentation. 
Repeated elimination of 28 m/e corresponds to 
two carbon monoxide molecules, which has been 
observed with coumarins. This is followed by 
elimination of a methoxyl group (m/e 157, 
129). If we now proceed to the compounds of 
the kawain type (Figs. 12, 13), we notice the 
appearance of a peak which may be considered 
an elimination of cinnamaldehyde. In addition 
there is a peak which corresponds to the rest of 
the molecule which remains after cleavage of 
cinnamaldehyde (M — 132) = 98. In this 
case cinnamaldehyde represents only a small 
fragment while the fragment corresponding to 
aldehyde minus hydrogen is larger. This how- 
ever is not true with the substituted derivatives. 
In these cases the aldehyde peak is of consider- 
able magnitude and no carbon monoxide elimina- 
tion takes place, which is observable in the un- 
substituted derivative. Furthermore, the intens- 
ity of various peaks is somewhat dependent on 
the substitution pattern of the aromatic part of 
the molecule. The most striking peak in the 
spectrum of the compounds of the kawain type 
is the peak which corresponds to a benzyl or a 
tropylium ion. This means that quite unex- 
pectedly cleavage takes place at a double bond. 
This is supposedly an artifact since presumably 
migration of the double bond precedes cleavage. 
Nevertheless, one can consider the possibility of 
a formal cleavage at positions with double 
bonds in the interpretation of the mass spectra. 
With substitution in the benzene ring the frag- 
ment is correspondingly displaced, that is, it is 
an indicator for the correct interpretation. 
Finally, there remains the interpretation of 
substances belonging to the dihydrokawain type. 
It proceeds normally with formation of a tropy- 
lium ion. Cleavage p is the normal reaction of 
saturated lactones. 
