Incorporation of Labelled Precursors into Psilocybin
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                             "Dilution"
                       (Spec. activity of precursor/
Precursor introduced    spec. activity of psilocybin)
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L-Tryptophan-H^3              132
Tryptamine-C^14                33
N-Methyltryptamine-H^3          2
N,N-Dimethyltryptamine-C^14    31
Psilocin-H^3                    6
DL-4-OH-Tryptophan-H^3       >500
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   The results (Table) show that 4—OH-tryptophan in contrast to tryptophan
(I) does not function as a precursor. Tryptamine (II) which is readily
formed from tryptophan by P. cubensis (3) serves as a better precursor of
psilocybin than tryptophan. N—Methyltryptamine (III) is a still better
progenitor of psilocybin but N,N-dimethyltryptamine (IV) is rather poorly
incorporated as judged from the dilution figures. However, if the poor
absorption of this compound by the fungus (less than 5%) is taken into
account, the high dilution factor does not make it an unlikely
intermediate. Psilocin (V) is effectively converted into psilocybin.
4-Hydroxytryptamine—C^14 is also incorporated into psilocybin but the
introduction of this compound led to the formation of one or two other
minor products not normally detectable in the cultures. Thus, it may be
questioned if this route via 4-hydroxytryptamine is normally occuring in
the fungus.