A. Fan, S.-M. Li / Tetrahedron Letters 55 (2014) 5199–5202
5201
(Scheme 1A).9 An orthologue 7-DMATSNeo from a Neosartorya sp.
was recently reported by Miyamoto et al.7 A few members of the
DMATS superfamily are responsible for the prenylation of non-
indole derivatives. For example, SirD from Leptosphaeria maculans
catalyses an O-prenylation of tyrosine (1a),10 the first step in the
product yield of 97% (Fig. 1G). That is about 2.7 times of that of 1a,
which might be explained by the electronic effect of this substitu-
tion on the benzene ring. The electron donating iodine at C3 posi-
tion would increase the nucleophilicity of the 4-hydroxy group for
dimethylallyl cation and stabilise the formed positively charged
ion, which is proposed to be intermediates in the prenylation reac-
biosynthesis of sirodesmin PL (Scheme 1B).11 SirD shares
a
sequence identity of 34% on the amino acid level with 7-DMATS
tions (Scheme 2).14,15 In comparison, 3-nitro-
L-tyrosine (7a) with a
and also catalyses the C7-prenylation of
L
-tryptophan, with a rela-
strong electron withdrawing group on the benzene ring was hardly
accepted by 7-DMATS (Fig. 1H). Introducing a second iodine to 6a,
as in the case of 8a, abolished the activity almost completely
(Fig. 1I). Similarly, a very low activity, with a conversion yield of
tive activity of 8.1% of that of 1a.10 Detailed investigations with
SirD also demonstrated the acceptance of several methylated and
halogenated tryptophan derivatives including 4-methyl-DL
tryptophan.12 Recently, Rudolf and Poulter have confirmed the
C7-prenylation of three indole derivatives including -tryptophan
-
2%, was observed for 3,5-dibromo-L-tyrosine (9a) (Fig. 1J). The
L
low conversion of 8a and 9a by 7-DMATS seems to be results of
steric hindrance of the two large substitutions at C3 and C5 of
the benzene ring. No product peak was observed in the reaction
and 4-methyl-DL-tryptophan by SirD.13 In addition, reversely N1-
prenylated derivatives were found as additional enzyme products
in that study (mostly as minor products). It seems that the tyrosine
O-prenyltransferase SirD shares similar catalytic activity with the
tryptophan C7-prenyltransferase 7-DMATS. Product formation for
1a was detected neither with 7-DMATS (after incubation with
mixture of
a
-methyl-L-tyrosine (10a) under this condition
(Fig. 1K). In comparison,
a-methyl-DL-tryptophan was accepted
by 7-DMATS with a relative activity of 19.1% of that of
L-
tryptophan.16
2.5
l
g recombinant protein for 45 min),8 nor with the recently
To elucidate their structures, the enzyme products of 1a, 3a and
6a were isolated on HPLC from 10 ml of incubation mixtures and
then subjected to NMR and MS analyses. MS data supported the
monoprenylation of the isolated products 1b, 3b and 6b by detec-
tion of molecular masses, which are 68 Da larger than those of the
respective substrates (Table S1 in Supplementary material).
Inspection of the 1H NMR spectra (Table S2; Figs. S1–S3 in
Supplementary material) of the isolated product peaks 1b, 3b
and 6b revealed the presence of signals for a regular prenyl moi-
ety each at dH 3.76–4.55 (d, H-10), 5.36–5.43 (t or tsept, H-20),
1.73–1.79 (s or d, H-40) and 1.69–1.79 ppm (s or d, H-50). Fur-
thermore, signals of the aromatic protons at dH 7.15 (d, H-2,6),
6.83 (d, H-3,5) of 1b; 7.22 (d, H-2,6), 6.89 (d, H-3,5) of 3b and
7.65 (s, H-2), 6.92 (d, H-5), 7.22 (d, H-6) of 6b indicated the
same number and coupling pattern as those of their respective
substrates. The 1H NMR spectra of 1b in DMSO-d6 and 3b in
D2O were almost identical to those of the enzyme products with
SirD,12 which confirmed the regular prenylation at the 4-hydro-
xyl group (1b) or 4-amino group (3b). Comparison of the spec-
trum of 6b with that of 1b, the signals of H-10 (4.55, d, 6.5)
and H-20 (5.43, tsept, 6.5, 1.5) of the prenyl moiety in 6b are
very similar to those of 1b. These data proved unequivocally
the regular prenylation of 1a and derivatives at O- or N-atom,
as summarised in Figure 1A. This means that 7-DMATS catalyses
both tryptophan C7- and tyrosine O-prenylation, as observed for
the tyrosine O-prenyltransferase SirD.10,12,13
identified 7-DMATSNeo 7
.
No data on the acceptance of 1a deriva-
tives by 7-DMATS and 7-DMATSNeo are available in the literature.
Therefore, we reinvestigated the acceptance of 1a and derivatives
by 7-DMATS from A. fumigatus with higher protein concentration
and longer incubation time than used in our previous studies.8
L-Tyrosine (1a) and nine derivatives (2a–10a, Fig. 1) were tested
as substrate with 20 g recombinant 7-DMATS in 100 L enzyme
l
l
assays at 37 °C for 16 h. HPLC analysis of the incubation mixtures
showed clear product formation in several cases (Fig. 1, B–K).
Detection was carried out with a photo diode array detector and
illustrated for absorption at 277 nm. As shown in Figure 1B, 1a
was accepted by 7-DMATS with a product yield of 36%. No product
formation was detected in the reaction mixture of its enantiomer
2a (Fig. 1C). Replacement of the phenolic hydroxyl group by an
amino group, as in the case of 4-amino-L-phenylalanine (3a),
increased the acceptance by 7-DMATS, with a product yield of
70% (Fig. 1D). Again, its enantiomer 4a was not converted by
7-DMATS (Fig. 1E), demonstrating the high stereoselectivity of
7-DMATS towards 1a and its derivatives. Therefore, L-configured
tyrosine derivatives were used for further study. Introducing an
additional hydroxyl group to C3 of tyrosine (5a) resulted in a
reduction of its acceptance by 7-DMATS, with a conversion yield
of 12% (Fig. 1F), approximate one third of that of 1a. Interestingly,
an iodine substitution to the ortho-position of the hydroxyl group
(6a) increased significantly the enzyme activity, with a remarkable
Scheme 2. Proposed mechanism of prenylation of tyrosine and derivatives by 7-DMATS.
Fan, Aili
