bone (Figure 14A) and – still more surprisingly – alkylphosphonocholines (Figure
14B) can be transesterified by means of PLD. These compounds possess antitumor
properties and are therefore important drugs (Eibl et al., 1992; Stekar et al., 1993).
The preference of certain PLDs for transesterification observed in the conversion of
PC, however, cannot be applied to the reactions of alkylphosphate esters (Aurich and
Ulbrich-Hofmann, unpublished results). Here, PLD from cabbage orStreptomyces
chromofuscuswas unambiguously more appropriate for transesterification than PLD
fromStreptomycessp. (Sigma).
As seen from Table 3 and Figure 13, the spectrum of chemical structures of al-
cohols which can be introduced as head group is wide, and ranges from small ali-
phatic alcohols to multi-ring systems. In general, primary alcohols are better accep-
tors than secondary ones, whereas no tertiary alcohol is known to be introduced.
D’Arrigo et al. (1994; 1996b) demonstrated that PLD fromStreptomycessp. is ap-
propriate to introduce also secondary alcohols into phospholipids, whereas PLD
from cabbage has long been considered to be incapable of accepting secondary al-
cohols (Ko ̈tting and Eibl, 1994). However, Hirche et al. (1997b) and Aurich et al.
(1997) have demonstrated recently withN-heterocyclic alcohols that PLD from cab-
bage is also suitable to transfer secondary alcohols to phosphatidyl or alkylphosphor-
yl moieties. A comparison of the ratios of the initial rates of transphosphatidylation
and hydrolysis for PLDs fromStreptomycessp. and cabbage reveals that the selec-
tivity for primary alcohols is greater for PLD fromStreptomycessp. than for PLD
from cabbage (Hirche and Ulbrich-Hofmann, 2000). In all cases studied so far the
formation of transphosphatidylation products is kinetically controlled, because most
products are again hydrolyzed as time advances (see Figure 12).
In addition to the examples given in Tables 3 and 4, some special applications have
been reported. Thus, PLD fromStreptomyces chromofuscushas been used to convert
lysophospholipids to cyclic lysophosphatidic acid (Friedman et al., 1996). In the
reaction sequence for the synthesis ofara-CDP-1,2-diacylglycerides, PLD from
Streptomyces chromofuscus has been used for the catalysis of an intermediate
step, including the removal of choline from 1,2-diacyl-sn-glycero-3-phosphocho-
line (Rebecci et al., 1993). Transphosphatidylation by PLD fromStreptomyces
sp. was also applied in the synthesis route of optically active hydroperoxides of
phospholipids (Yoneda et al., 1992).
12.5 Examples of application 249
Figure 14. Chemical structures of alkylphosphocholines (A) and alkylphosphonocholines (B).