ECD calculations confirm configuration of as
(R,R)
Reassign to
(R,R)
as well,
Establishing the as
retention
.
Ottenheijm's
epithiodioxopiperazine:
"(S,S)" [α]
D
-53°
obs
(R,R) [α]
589
-131°
calc
, corresponding to ~70% (R,R) and ~30% (S,S)