COMMUNICATIONS
Table 2. Peptide amidase catalyzed amidation of peptides in acetonitrile
containing 5% of water.[
[1] D. J. Merkler, Enzyme Microb. Technol. 1994, 16, 450 ± 456.
[2] K. Breddam, F. Widmer, J. T. Johansen, Carlsberg Res. Commun. 1981,
6, 121 ± 128.
3] F. Widmer, K. Breddam, J. T. Johansen, Carlsberg Res. Commun. 1981,
6, 97 ± 106.
a]
4
Peptide
Yield[%]
of amide
Precipitation of
tret [min]
[
ammonium salt amide peptide
4
Z-Gly-Phe-OH
Z-Gly-Leu-OH
Z-Gly-Tyr-OH
Z-Ala-Phe-OH
Z-Leu-Phe-OH
Z-Pro-Phe-OH
Z-Phe-Ala-OH
Z-Ala-Pro-Leu-OH
33.5
27.5
1.0
no
6.73
5.83
3.96
8.84
7.89
4.71
11.04
26.83
14.57
9.90
[4] S.-T. Chen, M.-K. Jang, K.-T. Wang, Synthesis 1993, 858 ± 860.
[5] H.-D. Jakubke, P. Kuhl, A. Könnecke, Angew. Chem. 1985, 97, 79 ± 87;
Angew. Chem. Int. Ed. Engl. 1985, 24, 85 ± 93.
[6] D. Steinke, M.-R. Kula, Angew. Chem. 1990, 102, 1204 ± 1205; Angew.
Chem. Int. Ed. Engl. 1990, 29, 1139 ± 1140.
yes[
yes
yes[
no
b]
c]
8.0
8.08
23.0
21.5
33.0
24.0
19.84
11.58
8.10
no
yes[
no
[7] D. Kammermeier-Steinke, A. Schwarz, C. Wandrey, M.-R. Kula,
b]
Enzyme Microb. Technol. 1993, 15, 764 ± 769.
Ï
8.75
10.75
[8] V. Ce rÏ ovsk y , K. Martinek, Collect. Czech. Chem. Commun. 1989, 54,
027 ± 2041.
9] U. Stelkes-Ritter, Dissertation, Universität Düsseldorf, 1994.
2
[
a] 0.025mmol of peptide, 0.035mmol of NH
4
HCO
3
, 2 mg of amidase,
[
0.50 mL total volume, 72 h, 408C. [b] Precipitation after 40 h. [c] Immedi-
ate precipitation.
groups in peptides is possible. The necessary enzyme can be
isolated from orange peel, a waste product of the juice
industry, by a simple two-stage extraction procedure that
yields 300 ± 500 U per kilogram of peel. Since the unchanged
peptide can be easily recycled, enzymatic amidation could be
economically feasable after further optimization.
Secondary Bonding between Chalcogens or
Pnicogens and Halogens**
[
9]
Gregory A. Landrum and Roald Hoffmann*
The more crystal structures we know, the clearer it becomes
that in the solid state there are many contacts in the range
between a bond and a van der Waals interaction. N. W. Alcock
introduced the useful term ªsecondary bondingº for these,
and formulated a set of rules for their occurrence and
directionality.[
For electron-rich main-group systems there are two popular
ways to address in a qualitative way the electronic structure of
secondary bonded speciesÐeither as a manifestation of
hypervalence (electron-rich three-center or multicenter bond-
Experimental Section
Typical procedure for the amidase-catalyzed amidation of peptides: The
reactions were carried out in 2-mL plastic tubes with screw caps, which
were incubated in a rotatory shaker at 1000 rpm and various temperatures.
The benzyloxycarbonyl dipeptide (0.025 mmol) was dissolved in acetoni-
trile (475 mL). The required water and ammonium concentrations were
1]
adjusted by the addition of water and 2m NH
calculated volume of 500 mL. After the addition of lyophylized amidase
2 mg), the suspension was shaken at 408C for several days. Before the
4 3
HCO to give the final
(
[2]
[3]
ing ) or as directional donor± acceptor bonding. We feel
these approaches are in fact equivalent, though we doubt that
the number of energetic electrons expended on the demerits
of one or the other chemical views is exhausted.
termination of the reaction, the apparent pH value of the mixture was
checked with indicator paper. The reactions were terminated by diluting
the mixture with 50% aqueous methanol (1.5 mL) containing 1%
trifluoroacetic acid (TFA). The product yield was estimated by HPLC on
an RP-18 column (Merck, WP-300, 5 mm, 25 Â 0.4 cm) operated isocrati-
�
1
In recent work we have used the concept of donor± ac-
ceptor interactions to interpret calculations on hypervalent
bonding in the trihalides and hydrogen bihalides,[ intermo-
cally with a mixture of methanol and 0.1% TFA (45/55) at 1 mLmin
.
Detection was carried out at 254 nm. The newly formed peak corresponded
to the peptide amide and had a retention time identical to that of a standard
sample. To follow the course of the amidase-catalyzed amidation of Z-Gly-
Phe-OH with time, reactions were performed in several test tubes and
terminated after a given time interval.
4]
[5]
lecular interactions in R QX (Q Se, Te; X I, Br, Cl), and
2
2
the secondary bonding in dimers of Ph IX and XF (X I, Br,
2
3
Cl).[ These studies, and the importance of directionality in
6]
Synthesis of Z-Gly-Phe-NH
dissolved in a mixture of acetonitrile (19 mL) and water (0.3 mL). After
a solution of NH HCO (0.7 mL, 2m) and amidase (80 mg) was added, the
mixture was shaken in a sealed vessel at 358C for 4 d. According to HPLC
analysis the yield of Z-Gly-Phe-NH was 31%. The neutral product was
2
: Z-Gly-Phe-OH (357 mg, 1 mmol) was
[7]
secondary bonding, have led us to look more broadly at the
nature of secondary interactions. In this work searches of the
Cambridge Structural Database[ (CSD) have been used to
determine the prevalence and geometries of secondary
bonding in crystals containing chalcogens or Group 15
4
3
8]
2
isolated by cation- and anion-exchange chromatography and crystallized
from ethyl acetate/petroleum ether to give 82 mg of dipeptide amide (23%
yield, pure according to TLC and HPLC analysis). The m.p. of 133 ± 1348C
]
[
*] Prof. Dr. R. Hoffmann, Dr. G. A. Landrum[
Chemistry and Materials Science Center
Cornell University, Ithaca, NY, 14853 ± 1301 (USA)
Fax: (1)607-255-5707
corresponds to that of standard sample. Amino acid analysis: Gly 1.00, Phe
0.99; FAB-MS: 356.1 [MH] .
[
7, 9]
The peptide amidase was isolated according to the literature procedure.
The lyophilized enzyme had an activity of 0.2 Umg with Z-Gly-Tyr-NH
as substrate. The peptides were purchased from Bachem (Germany), and
ammonium salts were obtained from Fluka (Switzerland).
�
1
2
[
] Current address
Institut für Anorganische Chemie, Technischen Hochschule
Professor-Pirlet-Strasse 1, D-52074 Aachen (Germany)
[
**] We are grateful to the National Science Foundation for its support of
our work through Research Grant CHE 94 ± 08455. We would also
like to thank Silicon Graphics for their generous donation of the
computer hardware which was used in this work. In the process of
preparing this work, we benefited greatly from insightful comments
by Hans-Beat Bürgi.
Received: February 10, 1998 [Z11456IE]
German version: Angew. Chem. 1998, 110, 1986 ± 1989
Keywords: amides ´ enzymes ´ enzyme catalysis ´ peptides
Angew. Chem. Int. Ed. 1998, 37, No. 13/14
ꢀ WILEY-VCH Verlag GmbH, D-69451 Weinheim, 1998
1433-7851/98/3713-1887 $ 17.50+.50/0
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