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On the Enigma of Chlorophyll Degradation The Constitution of a Secoporphinoid Catabolite.

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regeneration were carried out as described.I7. Developing
shoots were selected on 100 pgmL-' kanamycin.
Fifteen kanamycin resistant plants were tested for cyanamide hydratase a~tivity!~]Enzyme activity was found in all
plants, the level of expression ranging from 0.03 to 0.79 units
per mg protein in the cell extract. The highest value corresponds to about a fifth of the specific activity measured in
induced Myrothecium verrucaria extracts. Although the
specific activity was highest in the roots, the total enzyme
activity per gram fresh weight was distinctly higher in the
leaves than in the other plant organs (Table 1). No activity
was found in plants transgenic for cah-.
Table 1. Activity of cyanamide hydratase in extracts of various organs of tobacco plants transgenic for cah+.The organs were frozen in liquid nitrogen, pulverized, and then extracted with 5 m phosphate
~
buffer pH 8 (1 mLg-' fresh
weight) (specific enzymatic activity in the extract of the total plant:
0.276Umg-'). N o activity above background could be measured in cahtransgenic plants.
plant organ
activity
[units per g fresh weight]
specific activity
[units mg-' protein]
cah' roots
cahC stem
cuh' leaves
0.073
0.437
0.643
0.660
0.469
0.202
Rooting of wild type or cah- transgenic tobacco shoots is
completely depressed with 1.2 mM cyanamide in the medium.
In contrast, root formation of cah' transgenic axillary shoots
was observed even when the growth medium was supplemented with 12 mM cyanamide. Thus in respect to root formation, the tolerance to cyanamide is increased at least by a
factor 10. Rooted cah' transgenic plants grow well on at
least 2.4 mM cyanamide, a concentration that kills nontransformed or cah- transgenic plants within six weeks.
Plants nontransformed or transgenic only for the vector
pBinl9 are completely bleached within 15 days after being
sprayed once with 0.5 YOcyanamide solution. In contrast
cah' transgenic plants tolerate distinctly higher concentrations, which correlate with the level of cah' gene expression.
For example, a plant with a specific enzymatic activity of
0.58 units per mg protein in the cell extract showed no necro-
sis after being sprayed once with 5 YOcyanamide solution,
which is the herbizide concentration recommended for use in
agriculture (Fig. 1). Additional evidence for the expressed
cyanamide hydratase activity being responsible for the increased tolerance is the formation of urea in the plant. Extracts from leaves of cah' transgenic plants grown for several weeks in the presence of 2 . 4 m ~cyanamide contain
10-32 pmolurea per g leaves (fresh weight), which is absent
in controls grown without cyanamide.
These results clearly demonstrate that expression of cyanamide hydratase confers tolerance to cyanamide in transgenic tobacco by its degradation to urea. In the presence of
the urea-degrading enzyme urease found in many
p l a n t ~ , [ ~ the
- ' ~ subsequent
~
product of hydrolysis NH,'
may be used by the plant as a nitrogen source.
Received: July 5,1991 [Z4778 IE]
German version: Angew. Chem. 103 (1991) 1353
CAS Registry numbers:
cyanamide hydratase, 50812-20-9; cyanamide, 156-62-7; urea, 57-13-6
(11 J. Botterman, J. Leemans, Trends Genet. 4 (1988) 219-222.
[2] H. Stransky, A. Amberger, Z. Pflanrenphysiol. 70 (1973) 74-87.
[3] U. H. Maier-Greiner, B. M. M. Obermaier-Skrobranek. L M. Estermaier,
W. Kammerloher, C. Freund, C. Wulfing, U. 1. Burkert, D. H. Matern, M.
Breuer, M. Eulitz, 0. 1. Kufrevioglu, G. R. Hartmann, Proc. Natl. Acad.
Sci. USA 88 (1991) 4260-4264.
[4] R. Topfer, V. Matzeit, B. Gronenborn, J. Schell, H.-H. Steinbiss, Nucleic
Acids Res. 15 (1987) 5890.
[5] M. Bevan, Nucleic Acids Res. 12 (1984) 8711-8721.
[6] A. Hoekema, P. R. Hirsch, P. J. J. Hooykaas, R. A. Schilperoort, Nature
(London) 303 (1983) 179-180.
[7] R. B. Horsch, J. E. Fry, N. L. Hoffmann, D. Eichholtz, S. G. Rogers, R.
T. Fraley, Science (Washington D.C.) 227 (1985) 1229-1231.
[8] J. Draper, R. Scott, (Eds.): Plant Generic Transformation and Gene Expression: A Laboratory Manual, Blackwell, Oxford 1988.
191 M. Damodaran, P. M. Sivaramakrishnan, Biochem. 1 31 (1932) 10411052.
1101 T. A. Skokut, P. Filner, Plant Physiol. 65 (1980) 995-1003.
[I11 H. M. Davis, L. M. Shih, Phyrochemistry 23 (1984) 2741-2745.
(12) Y. Chen, T. M. Ching, Plant Physiol. 86 (1988) 941-945.
On the Enigma of Chlorophyll Degradation:
The Constitution of a Secoporphinoid Catabolite**
By Bernhard Krautler,* Bernhard Jaun, Karlheinz Bortlik,
Maja Schellenberg, and Phiiippe Matile
Dedicated to Professor Vladimir Prelog
on the occasion of his 85th birthday
The degradation of the green plant pigment chlorophyll,
which lies behind the impressive natural phenomenon of fall
colors of trees and shrubs, is still not understood.['S2] This
gap in our knowledge131exists because the degradation of
chlorophyll "apparently takes place without leaving any
traces",""] although annually on earth probably over lo9 t
of chlorophyll is ~ a t a b o l i z e d .Only
~ ~ ] lately did the prospect
of gaining insights into the chlorophyll metabolism arise out
of the discovery of almost colorless plant metabolites, the
most important of which were characterized as tetrapyrrole
['I
Fig. 1. Cyanamide tolerance in transgenic tobacco. Nicoriana rabacum SR1
plants transgenic for cah' or pBinl9 with 6-8 leaves were sprayed once with
5 % cyanamide solution. The plants were maintained under sterile conditions in
a growth chamber (16 h photo-period, 25/18"C). The photographs were taken
after 15 days. Left: plant transgenic for pBinl9; right: plant transgenic for
cah .
+
Angew. Chem. Int. Ed. Engl. 30 (1991) No. 10
0 VCH Verlagsgesellschaft mbH.
[**I
Priv.-Doz. Dr. B. Krautler, Dr. B. Jaun
Laboratorium fur Organische Chemie
der Eidgenossischen Technischen Hochschule
Universitatstrasse 16, CH-8092 Zurich (Switzerland)
Prof. Dr. P. Matile, Dr. K. Bortlik, M. Schellenberg
Institut fur Pflanzenphysiologie der Universitat Zurich.
This work was supported by the Schweizerischen Nationalfonds und der
ETH-Zurich. We thank Prof. A. Eschenmoser for stimulating discussions
and Dr. WAmrein and R. Hufliger for acquiring the mass spectra.
W-6940 Weinheim. 1991
0570-0833/91/1010-1315 $ 3 . 5 0 f . 2 5 / 0
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derivatives by isotope labeling.[’. 4 - 6 1 Among these metabolites the “fluorescent compounds” (“FC’s”) were suggested
as precursors of the “rusty pigments” (“RPs”),[~~
based on
their appearance first in the chloroplasts and then in the
vacuoles of yellowing barley primary leaves. The RP’s owe
their name (and their discovery) to the observation that on
isolation in air and in the presence of acid they are transformed into easily visible, rust-colored secondary products.[1,4,51 We report here on the research resulting from
cooperation between a botanical and a chemical laboratory,
which led to the elucidation of the constitution of “RP14”,[51the major representative of the rusty pigments from
senescent barley primary leaves. The proposed constitution
of RP-14 as the I-formyl-19-oxobilane (3)[’] substantiates its
relationship with chlorophyll a (1) and provides the first
structural guideline which may help to unravel the mystery
of how chlorophyll is catabolized.
\\
R’
.OH
Fig. 1 . Primary leaves of barley (Hordeum vulgare cv. Gerbel and the structural
formulas for chlorophyll a (1) and for the catabolite “RP-14” (3); left: freshly
cut; right: as left, after 7 days aging in darkness [4a, 51).
spectrum in [D,]DMSO (6, = 4.63, 6, = 3.91, JA,, =
3.3 Hz, assigned to H-CIS and H-C13’) is missing in the
D,O system as a result of H/D exchange. Of the 35 carbon
atoms, signals for 33 are resolved in the 13CNMR spectrum
(100 MHz) of 3-K in D,O: the signal of C13’, deuterated in
D,O, cannot be found; the spectrum in [D,]DMSO shows 32
signals including that for C13’ at 6 = 64.99.
1 (Chlorophyll a): R ’ = Me, R: = C(O)OMe,
3 - K “RP-14” (K sol1 1 MG=K@
R i = H, R 3 = phytyl
2 (Chlorophyll b): R’ = CH(0). R: = C(0)OMe.
R; = H, R3 = phytyl.
4 (Chlorophyllide a. Na salt): R’ = Me,
R: = C(O)OMe, Rg = H, R3 = Na
5 (13-Hydroxychlorophylla): R‘ = Me,
R i = C(0)OMe. R i = OH, R 3 = phytyl
6 (Pyrochlorophyllide a, Na salt): R’ = M e ,
R: = H. R; = H, R3 = Na
To obtain a sample of the plant metabolite RP-14 (3), the
primary leaves of the barley mutant Hordeum vulgare cv.
Gerbel were aged in the dark as described before[4a.
(Fig. l), and the cryosap isolated from it was separated by
HPLC. The eluate that contained the potassium salt 3-K as
major component (94 %, HPLC analysis) was lyophilized,
and the salts removed from the residue on C-18 cartridges.
The metabolite 3-K was isolated as a powdery lyophilization
residue (see Experimental Procedure).
The constitution of RP-14 (l-formyl-l9-oxobilane, 3) was
deduced from MS, ’H and 13CNMR, UVjVIS, CD, and IR
spectra: the molecular formula of 3-K was given as
C3,H4,N4010Kin the FAB mass spectrum[sa1in positive-ion
mode: molecular ion at m / z 717.266 (C,,H,,N,O,,K
717.254); base peak at mjz 679.287 (C,,H43N4010679.298);
in negative-ion mode the base peak was at mjz 677.4. The
absorption maximum of the longest wavelenth band in the
UVjVIS spectrum of 3-K (cf. ref. [5]) at 315 nm is consistent
with an a-formylpyrrole unit, but not with an extended, conjugated chromophore. In the ‘H NMR (400 MHz) spectrum
of 3-K in D,O ([D,]DMSO), the signals of 33 (40) of the 41
protons can be seen (Figs. 2 and 3 a): a singlet for the formyl
proton and five singlets for methyl protons, including, according to the chemical shift, an ester methyl group; signals
due to unsubstituted ethyl and vinyl groups are not observed. The signal at higher field of an AX system in the
1316
0 VCH
Verlagsgesellschaft mbH, W-6940 Weinheim, 1991
8
7
5
6
4
3
2
I
-&
Fig. 2. ‘H NMR spectrum (400 MHz) of 3-K in D,O at 25°C. (dHW 4.72, c =
ca. 3.5 mM): The signal of H-C13* is missing because of H-D exchange; the
signal of H-Cl5 at 6 = 4.83 is therefore a singlet.
In addition to the five methyl groups, the H atoms bound
to 0 and N atoms, and the formyl-H atom, six isolated spin
systems of 3-K are recognized on applying homonuclear ‘H
chemical shift correlation (DFQ-COSY, TOSCY[sh-e]).The
corresponding 13CNMR signals were identified by ‘H,13ClJH.cchemical shift correlation.[8‘. g1 Through information
about the spatial neighborhoods from ‘H nuclear Overhauser measurements (NOESY,[sb,h*i1 Fig. 3 a) and support-
0570-0833/91/1010-1316$3.50+.25/0
Angew. Chem. Int. Ed. Engl. 30 (1991) No. 10
0
-.
bl
,.
h
Fig. 3. a) Assignments and chemical shifts of the proton signals of 3-K (D,O, 2 5 T , NZ)and NOE correlations observed in the NOESY spectrum [8 b] (D,O/MeOH
1:1, - 7.5"C,N,; w = weak, m = medium, s = strong); b) assignments and chemical shifts of the I3C NMR signals of 3-K (D,O, 2 5 T , N,; additional values in italics
are for those signals in the spectrum of 3-K in [DJDMSO that show additional correlations to those in D,O in the HMBC spectrum [Si, j]). Z'3J(C,H)correlations
are represented as arrows that start at protons and point to the correlated I3C atoms (solid for D,O, dashed for (D,]DMSO). In the [DJDMSO spectrum the H-N21
and H-N24 show additional 2'3J(C,H) correlations to all four C atoms of the corresponding pyrrole rings A and D .
ed by H-C long-range connectivities from HMBC spectra
(HMBC = Heteronucluear Multiple-Bond Connectivity,[*jl
Fig. 3 b), the connectivities of the C-centers and the C- and
I?-bonded H atoms of the B-C part (C5 to C13) and the A-D
region (C14 to C4, including C13' and C13') of 3-K were
deduced, to which the four pyrrole N atoms could be fitted
in a satisfactory way. The three 0 atoms which were not
already assigned to carbonyl, ester, or carboxylato groups
could be identified as hydroxy substituents at positions 3',
32, and 82 from FAB-MS, I3C, and 'H NMR data. The
coupling of the A-D and B-c halves through an annelated
cyclopentanone ring was concluded from the following: a)
The molecular formular of 3-K implies 17 double-bond
equivalents, of which three are involved in the coupling in
question. b) The I3C chemical shifts of the three C atoms
involved (6 = 127.4, 163.5, and 194.9) indicate that two are
olefin (arene) atoms for which two CT bonds are observed and
another is a ketone C atom for which the second C-C bond
is missing. The exclusion of highly strained systems leads to
the coupling through the cyclopentanone annelated to the
pyrrole ring C, and the three C atoms are identified as C13,
C14, and C13'. (A related structural problem has been described.["')
The analysis of all the spectroscopic data suggests that
the constitution of 3-K is that of a potassium-4,5seco-4,5-dioxo-3', 32,82- trihydroxy - 13' -methoxycarbonyl1,4,5,10,15,20-(22H,24H)-octahydrophytoporphyrinate.
The
configuration of the four stereogenic centers, which apparently are largely uniform in optically active 3-K, has still not
been ascertained. However, from 'H NMR data the
methoxycarbonyl group at the 132-positionof the cyclopentanone ring is trans to the AD half. Thus 3-K presumably is
the thermodynamically more stable diastereomer with respect to this part of the molecule (but it possibly forms in
vitro on H exchange in a protic milieu).
A feature of 3 is the methoxycarbonyl-substituted cyclopentanone ring, which is a structural characteristic of the chlorophyll derivatives such as 1 and 2. This and the occurrence of
four methyl groups bonded to the chromophore in 3 shows
a close structural correspondence between 3 and 1 (and less
so with 2), but not with the chlorins 5r11a1
and 6" lbl suspectAngew. Chem. Int. Ed. Engl. 30 (1991) No. 10
0 VCH
ed to be chlorophyll catabolites: compound 3 is formally
accessible from chlorophyllide a (4), which has been postulated as the first degradation product of chlorophyll a
(l)!'",' 2 * t 3 1 by demetalation and addition of one oxygen
molecule and three water molecules; its chiroptic properties
suggest an enzyme-controlled formation (cf. the current
speculations on chlorophyll degradationr3.l4l).
Recently the light-emitting substance of krill (a part of the
sea plankton) and luciferin from dinoflagellates have been
characterized as the first examples of naturally occurring
"bile pigments" structurally derived from chlorophyll.[101In
these substances the chlorin macrocycle is interrupted at the
meso position C20, a site of the chlorin ring which is readily
In contrast, the macroattacked by electrophilic
cycle in 3 is opened at the meso position C5, which recalls the
161
oxygenolytic degradation of the iron porphyrin heme
to bile pigments.
The constitution of the 4,5-seco-4,5-dioxophytoporphyrinate 3-K provides for the first time a structural guideline
which may contribute to the understanding of the apparently
complex process of chlorophyll degradation.
Experimental Procedure
For the cultivation of Hordeum vulgure cv. Gerbel and the conditions of the
senescence induced in the dark, see [4a, 51: 115 g of leaves were aged in continuous darkness for 7 d; the cryosap from 5 g batches of leaf material (ca. 4 mL)
was treated with acetone (ca. 16 mL) and centrifuged to separate the protein
material (5 min per 2300 g). The supernatant was treated with chloroform
(20 mL), briefly shaken, and the aqueous phase separated into two portions
(HPLC column, Stagroma, Wallisellen, Switzerland): Nucleosil RP-8, 10 pm,
20 x 250 mm; eluant: 27 vol% methanol/73 vol% 50 mM potassium phosphate
pH 7; flow rate 14.6 m l m i n - ' ;detection at 320 nm.The fraction with a retention of ca. 17.3 min was collected at 0°C under an inert atmosphere (N,). The
crude fractions of 3-K were lyophilized in three portions at room temperature,
the residue extracted three times with ca. 3 ml portions 20 vol% aqueous methanol and the extracts purified in five portions by HPLC as described. The
HPLC eluates were stored for 3-8 days under nitrogen at - 20°C and then
lyophilized in two portions at T < 0°C; the pale yellow residue of each batch
was placed on a Waters C,, Sep-pak cartridge with ca. 2 mL destilled water and
washed with ca. 25 mL destilled water. A pale yellow fraction was eluted with
ca. 20 mL 20 vol% aqueous methanol and the eluate lyophilized under high
vacuum at T < 0°C. The light yellow residue of powdery 3-K was dried under
high vacuum at room temperature for ca. 4 h. Yield 13 mg (> 94%; analytical
HPLC, cf. [5]).
Verlagsgesellschuft mbH, W-6940 Weinheim, 1991
O570-0833/9l/lOIO-1317 $3.50+.25/0
1317
Spectroscopic data: (NMR: Bruker AMX-400, 'H NMR in D,O: cf. Fig. 2 and
3a, 13CNMR in D,O: cf. Fig. 3b). 'H NMR (400 MHz, ca. 4 m solution
~
under N,, [DJDMSO): 6 = 1.84, 1.85 (2s. H,C (2' and 18')), 2.00, 2.17 (2s.
H,C (12', 7')), overlapping with 2.0-2.2 (m, H,C (17')), 2.31 (dd,
J(H,H) = 8.7114.5 Hz, H,C(20)), 2.4-2.6 (m.H,C(8*) and H,C(17l)), 2.6-2.7
(m, H,C(17')), 2.72 (dd, J(H,H) = 4.9/14.5 Hz, H,C(20)), 3.2-3.3 (m,
HzC(S2)), 3.3-3.5 (m, H2C(3')), 3.62 (s, ester CH,), 3.70/3.79 (AB spin
system, J(H,H) = 15.8, H,C(lO)), 3.91 (d, J(H,H) = ca. 3.5 Hz, HC(13z)) overlapping with 3.94(dd, J(H,H) = 4.9/8.7 Hz, HC(l)), 4.33 (t. J(H,H) ca. 5.6 Hz,
HC(3')), 4.63 (d, J(H,H) = 3.3 Hz, HC(15)), overlapping with 4.6-4.7 (br,
1 H), 4.7-5.0 (br, 1 H), 7.79 (s, HN(21)), 9.49 (s, HC(5)), 9.85 (s, HN(24)).
11-13 (br, ca. l H ) , 13.0-13.2 (br, 1 H)); 13C NMR (100 MHz, ca. 15 mM
solution under N,, [DJDMSO): 6 = 9.04(7',12'), 9.30(18'), 12.20(2l),
21.68(17'), 22.47(10), 27.35(8'), 29.66(20), 35.52(15), 39.6(17*), 51.92 (ester
CH,), 60.15(1), 61.01(8'), 64.63(3'). 64.99(13'), 67.64(3'). 108.42(12).
113.25(18), 119.20(8,17), 122.54, 122.62(13,16), 122.99(19), 127.9 (br, 6).
130.86(3), 132.95(11), 136 (br, 9), 154.94(2), 159.86(14), 170.43(133), 172.52(4),
177.30(17% 178 (br, 5). 188.15(13'). UVjVIS and CD (0.02 M sodium phosM): i.,,,[nm] (rel. E ) = 243 (0.83), 272 (sh, 0.59), 315
phate, pH 7, c =
(1.0,log~=4.2);hm,,[nm](bs) =223(15),247(- 4),282(- 14),317(4).FABMS (3-nitrobenzyl alcohol matrix, ZAB-2 SEQ, cesium bombardment,
35 keV): a)positive-ion mode: m / z 755.1 (10%); 719.2 (20). 718.2 (60), 717.2
(90% C3,HaN,O,oK, [M l]@); 681.2 (12). 680.2 (55). 679.2 (100,
C3JLN,Oio,
[ M 2 - K]@), 678.2 (30), 677.2 (12). 560.1 (12,
C2,H,,N,0,K, [ M 1 - Ring A]@), 523.2 (28), 522.2 (65, C,,H,,N,O,,
[ M + 2 - K - Ring A]"); exact mass determination (OPUS-V 1.5Dsoftware,
internal matching with matrix references at m / r 651.134, 613.178, 498.091,
460.136; resolution: ca. 1500): m/z C 717.266 (95%, C,,H,,N,Ol0K, 717.254);
679.298); 522.213 (65, C,,H,,N,O,, 522.224);
679.287 (100, C,,H,,N,O,,,
b) negative-ion mode: m/z 679.4 (15%), 678.4 (46), 677.4 (100, C,,H,,N,O,,,
[ M - Kle). 676.4 (30); IR (0.3%. Perkin Elmer-983, KBr): qcm-'] =
2950(m), 2920(m), 2860(m), 1725(m), 1670(s), 1630(s), 1560(m), 1490(m),
1445(m), 1390(m), 1345(m), 131O(m), 1275(m).
+
Anti-Selective and Diastereofacially
Selective Aldol Reactions with (R)2-Siloxy-l,2,2-triphenylethyl propionate**
By Manfred Braun* and Hubert Sacha
Dedicated to Professor Leonhard Birkofer
on the occasion of his 80th birthday
The directed synthesis of the enantiomeric syn-b-hydroxycarbonyl compounds 1 and ent-1 is achieved today with
highly etficient variants of the aldol reaction, mostly starting
from chiral propionamides. In contrast, anti-selective aldol
reactions, based on the addition of chiral propionic acid
esters to aldehydes RCHO, are known to be problematic
partly because of poor simple diastereoselectivity (anti-1 versus syn-1) and partly unsatisfactory diastereofacial selectivity (2 versus ent-2).['' Lately more effective enolates and silyl
+
+
Received: May 29, 1991 [24664 IE]
German version: Angew. Chem. 103 (1991) 1354
CAS Registry numbers :
1, 479-61-8; 3, 135972-64-4; 3 . K, 136144-63-3
[l] a) P. Matile, Chimia41(1987)376; b) P. Matile, T. Duggelin, M. Schellenberg, D. Rentsch, K. Bortlik, C. Peisker, H. Thomas, Plant PhysioL
Biochem. 29 (1989) 595.
[2] W. Rudiger, S. Schoch, Nafurwissenschaften 76 (1989) 453.
[3] G. A. Hendry, J. D. Houghton, S. B. Brown, New Phyfol. f07(1987) 255.
(41 a) P. Matile, S. Ginsburg, M. Schellenberg, H. Thomas, J. Plant Physiol.
129 (1987) 219; b) T. Duggelin, M. Schellenberg, K. Bortlik, P. Matile, J.
Plant Physiol. 133 (1988) 492; c) P. Matile, S. Ginsburg, M. Schellenberg,
H. Thomas, Proc. Natl. Acad. Sci. USA 85 (1988) 9529.
[5] K. Bortlik, C. Peisker, P. Matile, J. Plant Physiol. f 3 6 (1990) 161.
[6] C. Peisker, H. Thomas, F. Keller, P. Matile, J. P/anf Physiol. 136 (1990)
544.
[7] For tetrapyrrole nomenclature see a) G. P. Moss, Pure Appl. Chem. 59
(1987) 779-832; b) H. Falk: The Chemistry of Linear Oligopyrroles and
Bile Pigments, Springer, Wien 1989.
[S] a) C. Fenselau, R. J. Cotter, Chem. Rev. 87 (1987) 501; b) H. Kessler, M.
Gehrke, C. Griesinger, Angew. Chem. 100 (1988) 507; Angew. Chem. Inf.
Ed. Engl. 27 (1988) 490; c) M. Rance, 0. W. Ssrensen, G. Bodenhausen, G.
Wagner, R. R. Ernst, K. Wuthrich, Biochem. Biophys. Res. Commun. 117
(1983) 479; d) L. Braunschweiler, R. R. Ernst, J. Magn. Reson. 53 (1983)
521 ;e) A. Bax, D. G. Davis, ibid. 65 (1985) 355; f) L. Muller, J. Am. Chem.
Soc. 101 (1979) 4481; g) A. Bax, S. Subramanian, J. Magn. Reson. 67
(1986) 565; h) J. Jeener, B. H. Meier, P. Bachmann, R. R. Ernst, J. Chem.
Phys. 71 (1979) 4546; i) S. Macura, R. R. Ernst, Mol. Phys. 41 (1980) 95;
j) A. Bax, M. F. J. Summers, J. Am. Chem. SOC.108 (1986) 2093.
[9] a) A. Gossauer: Chemie der Pyrrole, Springer, Berlin 1974; b) C. Pasquier,
A. Gossauer, W. Keller, C. Kratky, Helv. Chim. Acfa 70 (1987) 2098.
[lo] a) H. Nakamura, B. Musicki, Y.Kishi, J. Am. Chem. SOC.110 (1988) 2683;
b) H. Nakamura, Y. Kishi, 0. Shimomura, D. Morse, J. W Hastings, ibid.
111 (1989) 7607.
[l I ] a) M. J. Maunders, S. B. Brown, H. W. Woolhouse, Phytochemistry 22
(1983) 2443; b) R. Ziegler, A. Blaheta, N. Guha, B. Schonegge, J. Plant
Physiol. 132 (1988) 327.
[12] H. Thomas, K. Bortlik, D. Rentsch, M. Schellenberg, P. Matile, New
Phyfol. I f 1 (1989) 3.
[13] D. Amir-Shapira, E. E. Goldschmidt, A. Altman, Proc. Natl. Acad. Sci.
USA 84 (1987) 1901.
[I41 S. B. Brown, K. M. Smith, G. M. F. Bisset, R. F. Troxler, J. Biol. Chem.
255 (1980) 8063.
[15] a) R. B. Woodward, V. Skadc, J. Am. Chem. SOC.83 (1961) 4676; b) J.-H.
Fuhrhop, J. Subramanian, Philos. Trans. R. SOC.London 8273 (1976) 335.
[16] R. Schmid, A. F. McDonagh in D. Dolphin (Eds.): The Porphyrins,
Vol. V l , Academic Press, New York 1979, p. 258.
1318
0 VCH
Verlagsgesellschaff mbH, W-6940 Weinheim. 1991
ent-1
1
2
ent- 2
ketene acetals have been developed as starting materials, but
their synthesis has been hampered by the difficult access to
the required chiral auxiliaries.[21We now report the first antiselective and diastereofacially selective aldol additions of the
propionate 4b;its chiral building block, triphenylglycol, is
easily accessible in both enantiomeric forms (3 and ent-3)
and it has repeatedly proved its worth as the
The esterification of the (R)-diol3 with propionyl chloride
took place as anticipated, exclusively at the secondary hydroxy group, and afforded the propionate 4a, which was
in
transformed into the propionate 4b by O-~ilylation[~I
90 % total yield (Scheme 1, Table 1). The lithium enolate 5 a,
Table 1. Adducts 6/7, formed by addition of the enolate 5b to an aldehyde
RCHO.
R
6-9 Yield [a]
6/7:8/9 (anfi:syn)
617
[a] Crude yield in [%I.
formed in situ from 2-siloxy-l,2,2-triphenylethylpropionate
(4b) deprotonated by lithium cyclohexylisopropylamide,undergoes transmetalation with [Cp,ZrCI,] to form 5 b. Subsequent addition of an aldehyde yields predominantly the anti
diastereomers 6/7(Table 1). Their contribution to the product distribution was determined by NMR spectroscopy
(Table 2). At the same time this aldol addition shows a high
diastereofacial selectivity : the diastereomeric ratio of 6:7 lies
between 97:3 and > 98:2.
[*] Prof. Dr. M. Braun, Dip].-Chem. H. Sacha
Institut fur Organische und Makromolekulare Chemie der Universitat
Universitatsstrasse 1, W-4000 Dusseldorf 1 (FRG)
[*'I This work was supported by the Deutsche Forschungsgemeinschaft, the
Fonds der Chemischen Industrie, and BASF AG (gift of chemicals).
0570-0833/9~/1010-1318
$3.50+.25/0
Angew. Chem. I n f . Ed. Engl. 30 (1991) No. 10
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constitutions, catabolite, degradation, enigma, secoporphinoid, chlorophyll
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