A. Sesquiterpenoids
5
recently been isolated by de Mayo et al. (1965) from cedarwood of Cedrela
toona. A semisynthetic sample, which was obtained by Joshi and co-workers
(1964) as a result of aromatization of khushinol with 7V-lithioethylenediamine, had a small positive rotation, [«] D +0.88°. Apparently this sample
represents a largely racemized substance. The small positive rotation may
well be zero within the experimental error since the Indian workers do not
specify whether rotations were determined visually or photoelectrically.
Another semisynthetic sample which was prepared by Trivedi et al. (1966)
from khusinol with boron trifluoride etherate, had a rotation of [a] D + 82.58°.
The calamenene from the gorgonian had [a]^
5
° + 55.4°.
4
5
The third hydrocarbon in this group isolated from Eunicea mammosa
is (+)-a-muurolene (5), [αβ
5
° +67.Γ (Weinheimer et al, 1968b). It is,
except for rotation—and therefore configuration—identical with the
terrestrially derived ( —)-a-muurolene, [a]i>
2
° — 52.5° of Zabza and co-workers
(1966).
6
7
From the gorgonian Eunicea mammosa Weinheimer et al. (1970) isolated
the related three compounds ( + )-ß-elemene (6), (-)-germacrene-A (7), and
( — )-ß-selinene (8). ( + )-ß-Elemene (6) had been obtained earlier from the
same animal species which led to the authors' suspicion (Weinheimer et al,
1968) that they might be dealing with an artifact and that the natural sesquiterpene was of the germacrene type that underwent a Cope rearrangement
during work-up. Using gentle isolation procedures, Weinheimer et al. (1970)
isolated germacrene-A (7) and confirmed its ready isomerization to ß-elemene
(6) at elevated temperature or on silicic acid adsorbents. The degree of
stereospecificity of this rearrangement poses an intriguing question that
cannot be answered because of a lack of data. The gorgonian-derived ß-elemene is dextrorotatory, [αβ
50 +15.Γ, as is the ß-elemene isolated by Irie
5
recently been isolated by de Mayo et al. (1965) from cedarwood of Cedrela
toona. A semisynthetic sample, which was obtained by Joshi and co-workers
(1964) as a result of aromatization of khushinol with 7V-lithioethylenediamine, had a small positive rotation, [«] D +0.88°. Apparently this sample
represents a largely racemized substance. The small positive rotation may
well be zero within the experimental error since the Indian workers do not
specify whether rotations were determined visually or photoelectrically.
Another semisynthetic sample which was prepared by Trivedi et al. (1966)
from khusinol with boron trifluoride etherate, had a rotation of [a] D + 82.58°.
The calamenene from the gorgonian had [a]^
5
° + 55.4°.
4
5
The third hydrocarbon in this group isolated from Eunicea mammosa
is (+)-a-muurolene (5), [αβ
5
° +67.Γ (Weinheimer et al, 1968b). It is,
except for rotation—and therefore configuration—identical with the
terrestrially derived ( —)-a-muurolene, [a]i>
2
° — 52.5° of Zabza and co-workers
(1966).
6
7
From the gorgonian Eunicea mammosa Weinheimer et al. (1970) isolated
the related three compounds ( + )-ß-elemene (6), (-)-germacrene-A (7), and
( — )-ß-selinene (8). ( + )-ß-Elemene (6) had been obtained earlier from the
same animal species which led to the authors' suspicion (Weinheimer et al,
1968) that they might be dealing with an artifact and that the natural sesquiterpene was of the germacrene type that underwent a Cope rearrangement
during work-up. Using gentle isolation procedures, Weinheimer et al. (1970)
isolated germacrene-A (7) and confirmed its ready isomerization to ß-elemene
(6) at elevated temperature or on silicic acid adsorbents. The degree of
stereospecificity of this rearrangement poses an intriguing question that
cannot be answered because of a lack of data. The gorgonian-derived ß-elemene is dextrorotatory, [αβ
50 +15.Γ, as is the ß-elemene isolated by Irie