Title: Alternative Sweeteners

220 Kinghorn and Compadre
Figure 7 Structures of osladin and polypodoside A. (Glc d-glucopyranosyl; rha
l-rhamnopyranosyl.)
work also led to a structural revision from C-22S, C-25R, C-26S to C-22R, C-25S,
C-26R for this sweet P. glycyrrhiza constituent (54). Polypodoside A was found
to be nonmutagenic and not acutely toxic for mice when dosed by oral intubation
at up to 2 g/kg body weight (2). In subsequent sensory tests using a small human
taste panel, polypodoside A was assessed as exhibiting 600 times the sweetness
intensity of a 6% sucrose solution but also revealed a licorice-like off-taste and
a lingering aftertaste (2). Thus, the potential of polypodoside A for commercialization
is marred by its relative insolubility in water, its sensory characteristics,
and difficulties in collecting P. glycyrrhiza rhizomes (2). Despite the fact that
osladin has now been subjected to total synthesis, it is probable that this compound
will have similar limitations to polypodoside A in terms of its potential
commercial prospects, as previously noted (1, 2).
5. Pterocaryosides A and B
Pterocarya paliurus Batal. (Juglandaceae) is a plant whose leaves are used by
local populations in Hubei province, People’s Republic of China, to sweeten
foods. Two sweet-tasting secodammarane saponins, designated pterocaryosides
A and B (Fig. 8), were isolated from an extract of the leaves and stems of P.
paliurus (55). These compounds differ structurally in only the nature of the
attached sugar (a d-quinovose unit in pterocaryoside A compared with an larabinose
unit in pterocaryoside B). Pterocaryosides A and B were shown not to
be toxic in bacterial mutagenesis and mouse acute toxicity tests and were rated
as about 50 and 100 times sweeter than 2% w/v sucrose, respectively (55). Ptero-