Communication
2
However, in comparison to the NMR spectra of prodigiosins
sodium borodeuteride reduction. [7’,7’- H ]-2-undecanoylpyr-
2
8
and 9 the line shapes of the aromatic protons of 10 were
role was synthesized by acylation of pyrrole magnesium chlo-
[22]
2
rather broad, particularly the signals for H-3, H-4, and H-19.
Other solvents such as CDCl , C D CD CN, and [D ]DMSO did
ride with [7,7- H ]-undecanoic acid, followed by ester hydrol-
2
ysis (see the Supporting Information). LC-ESI-MS analysis of 10
3
6
6
3
6
2
not result in better spectra compared to those in CD OD at
after feeding [1’,1’,7’,7’- H ]-2-undecylpyrrole to the red pheno-
3
4
+
298 K, but revealed the presence of three exchangeable NH
type revealed increased isotope peaks at m/z 614 ([M+3+H] ,
+
protons. The extended conjugated system of 10 with the addi-
tional pyrrole moiety in comparison to the prodigiosins 8 and
cyclic side chain labeled), m/z 615 ([M+4+H] , linear side
+
chain labeled), and 618 ([M+7+H] , both side chains labeled)
9
clearly causes the observed line broadening.
(see the Supporting Information). The observed incorporation
pattern into 10 proves that it consists of an analogous ten-
membered carbocylic ring as streptorubin B (9), because one
1
1
The H- H-COSY correlations of 10 accounted for one pyrrole
moiety substituted at position 2, two pyrrole rings substituted
at three carbon atoms, and one pyrrole moiety substituted at
deuterium atom was lost upon ring formation with [1’,1’,7’,7’-
1
2
the positions 2 and 5. In the H NMR spectrum of 10 the
H ]-2-undecylpyrrole (7’, see the Supporting Information). The
4
proton signal of the central carbon atom C-6, like that found
in the spectrum of undecylprodigiosin (8) or streptorubin B (9),
was missing, suggesting that the additional 2-undecylpyrrolyl
moiety of 10 is attached at this position. The attachment of
the 2-undecylpyrrolyl moiety to the streptorubin B core struc-
chiral carbon C-7’’ of the carbocyclic chain in coeligiosin B (10)
was assigned with S-configuration, as with that of streptoru-
[27,28]
bin B (9),
based on the similar circular dichroism spectrum
and the origin of the compound. At 298 K coeligiosin B (10)
shows interconversion of its possible atropisomers, whereas at
222 K three conformers were observed. Roesy measurements
suggest that the 2-undecylpyrrolyl moiety of the major isomer
of 10 stands out of the plane formed by the streptomycin B
core because of a clear correlation between C4 with C4’’ (see
the Supporting Information).
1
13
ture at the central carbon C-6 was also reflected in H- C-
HMBC correlations of H-4, H-19, and H-9 to C-6 (Figure 2C).
However, the cross signal of H-4 and H-19 to C-6 was very
weak (likely due to dynamic effects) and was only obtained by
1
13
4
using H- C-HMBC conditions favoring the detection of J sig-
nals (CNST13=5 Hz). The carbon atom C-6 was assigned to be
Because of its close relationship to streptorubin B (9) and its
occurrence in S. coelicolor, we named compound 10 coeligio-
sin B (Scheme 1).
1
13
quaternary at d 130.7 according to the absence of a H- C-
c
HSQC correlation, which fits with the assumption that C-6 of
1
0 is being substituted with the additional 2-undecylpyrrolyl
moiety.
In order to elucidate the carbocyclic ring in 10 we searched
for the H-4’’ signal for which the corresponding signal in strep-
Besides coeligiosin B (10), a closely related compound (11)
with a quasimolecular ion of m/z 613.48407, corresponding to
an elemental composition of C H ON , was found by LC-MS
40
60
4
analysis of the methanolic extract of the red phenotype.
Compound 11 differed from coeligiosin B (10) by two addi-
tional hydrogen atoms. In analogy to the prodigiosins, strep-
torubin B (9) and undecylprodigiosin (8), which also differ by
two hydrogens due to the carbocylic ring of the undecyl side
chain, 11 was suspected to be an undecylprodigiosin (8) with
an additional undecylpyrrolyl side chain and consequently we
named it coeligiosin A (11). The comparison of the MS/MS
spectrum of coeligiosin A (11) with coeligiosin B (10), undecyl-
prodigiosin (8), and streptorubin B (9) fully supported this as-
signment (see the Supporting Information). The quasimolecular
ion of coeligiosin A (11) fragments to a series of ions that re-
flect the 2 amu difference to coeligiosin B (3) (see the Support-
ing Information). However, compound 11 was produced in
such low amounts by the red phenotype that our deductions
based on mass spectrometry could not be supported by addi-
tional NMR spectra.
[
27]
torubin B (9) appears at d À1.44. The H-4 ’’ signal of 10 ap-
H
a
peared at d À0.83–À1.64, but it was very broad and thus
H
hardly visible (Figure 2B).
Because of the shortcomings of the NMR spectra of 10 in
CD OD at 298 K, the behavior of 10 at different temperatures
3
was studied. Cooling to 222 K led to significant changes in the
signal pattern (see the Supporting Information). The broad sig-
nals of H-4, H19, and H-3 changed to a set of signals indicating
the presence of three conformers (major, minor, and trace
isomer) of 10. Instead of the hardly visible signal of H-4 ’’ at
a
2
98 K, two well detectable signals at d À0.95–À1.06 and
H
d À1.52–À1.63 appeared for H-4 ’’ at 222 K. Although the
H
a
mixture of conformers of 10 at 222 K complicated the NMR
1
13
spectra, key H- C-HMBC correlations to the central atom C-6
appeared clearer than at 298 K (see the Supporting Informa-
tion). Based on the accumulated spectroscopic data we con-
cluded that the novel compound 10 is a streptorubin B deriva-
tive with an additional 2-undecylpyrrolyl moiety attached to
the central carbon atom (C-6) of the tripyrrole ring system of
prodigiosins (Scheme 1). As with streptorubin B (9), 10 was ex-
pected to contain a 10-membered meta-bridged butylcyclo-
heptylpyrrole moiety. However, due to overlapping signals, the
To rule out that coeligiosins might be formed during the
work-up, we analyzed colonies of the red phenotype directly
from SFM agar plates by MALDI-MS. Prodigiosins and coeligio-
sins were found and it became evident that coeligiosins were
produced by the red phenotype. Because the MALDI-MS detec-
tion worked very well, we also applied it to screen red colonies
of S. coelicolor M145 grown in the presence of different transi-
connection of the carbocyclic ring was not identified by NMR
2
2+
2+
2+
2+
2+
2+
but by feeding [1’,1’,7’,7’- H ]-2-undecylpyrrole (7’) to the red
phenotype and studying the incorporation of the deuterium
tion metal ions (Fe , Mn , Co , Ni , Cu , and Zn ). Most
4
2
+
transition metal ions apart from Fe induced the formation of
prodigiosins and coeligiosins (see the Supporting Information).
The induction of the prodigiosin biosynthesis and its alteration
2
atoms into 10 by LC-ESI-MS. [1’,1’,7’,7’- H ]-2-undecylpyrrole
4
2
(7’) was obtained from [7’,7’- H ]-2-undecanoylpyrrole by
2
Chem. Eur. J. 2015, 21, 6027 – 6032
6030
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim