The transformation of histidine side chain to non-coded asparagines

Article abstract of DOI:10.1016/0040-4039(91)80099-R

The transformation of the histidine side chain to that of N_ω-carbamoyl asparagine, N^ω-formyl asparagine, N_ω-benzoyl asparagine, β-cyano alanine and aspartic acid has been described, involving as the primary step, the Ru(VI

Full text of DOI:10.1016/0040-4039(91)80099-R

Tetr~edron Letters, Vo132, No 40, lyp 5615-5618, 1991
Printed in Great Bntam
0040-4039/91 $3 00 +
Pergamon Press plc
THE TRANSFORMATION OF HISTIDINE SIDE C H A I N TO N O N - C O D E D ASPARAGINES
Subramama Ranganathan*, Darshan Ranganathan* and Dipt: Bhattacharyya
Dept. of Chenustry, Indian Insutute of Technology, Kanpur-208 016, India
Abstract: The transformauon of the histIdine side chain to that of N°-carbamoyl asparagme, N°-formyl
asparagine, NO-benzoyl asparagme, ~-cyano alanme and aspart:c acid has been descnbed, revolving as the
primary step, the Ru(VIII) mediated scission of tmadizole 4,5-rr bond.
The transformation of coded amino acid side chains, m a protein environment, to potentially interesting
non-coded ones, would be useful illustrations of chermcal approaches to protein engineeringI Of equal
importance ts the characterization of co-amino acids, containing non-coded side chains, that are related either
metabolically or otherwise to a coded precursor, since, they could be reed either as potential mtub:tors or used
m
normal peptide synthesis to generate hormones of altered profile. From these perspectives, we have
examined the highly intricate, yet rapid, oxidative conversion of histIdine side chain to that of ~-ammo
aspartic acid that takes place in liver and bacteria revolving inudazole-4-hydroxylatlon z We have recently
been able to demonstrate a related chermcal functionalization by treatment of protected hist:dme with ~-tbutyl
todylbenzene which led to y-formarmdo glutamme side chain3
We report in thas commumcatlon that zn sttu generated Ru m consistently cleaves, fn'st the trmdazole
4,5-rr bond of the histldine side chain leading to the generation of an asparagme umt.
N~-Benzyloxycarbonyl hastidine methyl ester [N~-Z-Hls-OMe, 1(!)]4 wlth 2 2 mol percent of the
reagent - generated from RuC13.3H20 (Cat.) and 18 eqmv of periodate m H20 MeCN CCI4 - when shaken
m
a sealed vessel for 60 h, afforded Na-benzyloxycarbonyl-N°~-carbamoyl aspa:agme methyl ester
[Nct-z-N~°-CONH2-Asn-OMe, (2), mp 168-169°C, 22%]5 and N-benzyloxycarbonyl aspartic acid-co-methyl
ester [Z-Asp(~-OH)-OMe, 3(~), 25%)6 Fortmtously, product from primary ox:dation, namely,
tNa-benzoyl-NC°-formyl asparagme methyl ester [NC~-Bz-N~-Formyl-Aan-OMe, 5(5), nap 218-220°C] could
be :solated m 31% yields m addition to N-benzoyl aspart:c acid-co-methyl ester [Bz-Asp(~-OH)-OMe, 6(_6),
5615

5616
mp 127-128°C, (3~,%)], when Na-benzoyl/ustidine methyl ester [Na-Bz-I-hs-OMe, (4.4)], was reacted with
Ru vm and the sttrred reactmn rmxmre worked up, snmlar to that described previously6, soon after the
disappearance of [tic, 48 h]. Interestingly, treatment of 5~ wlth benzoyl chloride -pyndme yielded,
~
N-benzoyl-~-cyano a/anme methyl ester [Bz-Ala([~-CN)-OMe. ¢7,7J, mp 164°C, 37%] and Na-N~--dlbenzoyl
asparagme methyl ester [N~-N~--da Bz-Asn-OMe, 8(8), mp 143°C, (29%)].
Finally the general nature of the unldazole ~t,5-g bond rapture was demonstrated with tetrahydroben-
zmaidazole (9)7 Compound (9_), under condinons described for the (4)
~ ~5j + ~) change, afforded, as the
sole isolable product, mono N-formyl adaplc acid armde [I(.~Q.), mp 163-164°C, (25%)]
A
fortuitous outcome of the present study is that, as ratmnalized m Scheme i products arising from
cleavage of each of the 5 bonds of the tmldizole ring have made theft appearence
from the vantage of reaction mechamsms, the profile of the intermediate arising from path a, Scheme
1, is noteworthy In the present study, tins hlghly electropinhc substance yields products by water addation
In a prote/n envtromnent such an mtermechate can well glve rise to cross Imk.mg by interaction w~tfl proxunate
basic residues For example, eye lens protein detenoratmn has been shown to be assocmted with such cross
linking revolving mtermechates from Insndme side chain oxMatlons 9
Above all, tins commumcatlon has endeavoured to project the chermcal modzficatlon along metabohc
pathways as attractive routes to the generation of non-coded amino acid side chains having biological interest
Hisndme has proved its versatility here a/so, since it has been possible to transform its slde chain, m a pepnde
envtronment, to that of ~-fommrmdoglutamme3, N~°-carbamoyl asparagme, N~°-formyl asparagme, N~-benzoyl
asparagme, ~-cyano alanme and aspartlc acid. They could either, after de-protection '° be used m normal
peptlde synthesis or could be generated, m selective cases, by d~rect protein modification
Acknowledgements: We are grateful to Dr S. Bamezm, Mr
K DLxlt and Mr K Bhamagar for experimental
help. Financial assistance from UGC, DST, CSIR, New Deltu is gratefully acknowledged
R E F E R E N C E S AND NOTES
1.
Offord, R.E, Protein Engineering, 1987, 1L 151

5617
o
2
-,-
Z
\
) I<I > ,
0 ) <
- r '
II
U
II
z'r
On"
~
-i- CI:
o : ,
.,.:,
z
,.
u~,~t
o
°to ot
°t
°t
-r
N
U ~ .
-r
-r
Z
I
•"!-
"
/
Z
~
0
0
"°
h e . . .
I
u
0
U
-r
U
I
t
t °
(M
"r
U
I
~
"7" -r
~-~o
II
>.
||
n¢
I
N
t.)
~"
m
T
~.
n
~
N
0
Z
~"
Z C I : :
"r
u,z:.
o
..
Z
T~
U . - - -
n, @om
r,, t'-I
I
-r
T
t
°
0
Z
I
0
•-r
U
0
I
U
"-"
"r-
u
0
-f-
: C z
-+-
z - m ~'
I
N
I
n
ne
N
m
II
u
~ T . . .o
r~
ou
(3::
I
tt
°t
° ~
I!
n¢
f
t
"
i
I
I
u~l

5618
2.
Fourmer, J P, Bouthaller, L P, J Am. Chem Soc., 1952,
C h e m , 1954, 210, 559
~ 5210, Tabor. H., Mehler, A. J Blol
Ranganathan, S., Ranganathan, D, Smgh, S.K., Bhattacharyya, D, J. Chem Soc Chem Commun,
1987, i887
3.
All amino acids used were of the L configuranon. Starting materials as well as products were fixlly
characterized (ir, nrnr, ms) Elemental analysts, performed on all new compounds, were m good
agreement with expected values
Several attempts to prepare (2) from Asp or Asn failed In view of the potennal of (2) for use m
pepnde synthesls, detailed procedure for the I(!) --~ (2_) change is given below
A rmxture of (.k) (5 mmol), MeCN CC14.HzO (1 1 2. 80mL). NaIO~ (90 mmol) and RuC13-3HzO (2.2
mol%), was sealed, left shaken for 60 h, Filtered, residue washed with CCI~ (3x10 mL), the aqueous
layer extracted w~th EtOAc t3x30 mL), the combined orgamc extracts dried, evaporated,dagested wtth
satd. NaHCO3 (40 mL). extracted with EtOAc (3x30 mL),dned, evaporated and chromatographed over
sthca gel. Elutaon with Phil EtOAc (3.7) gave 22% of @, mp 168-169°C, lr v~l~ KBr cm t 3320,
1740, 1690, 1660,1530; ~H nmr ~ (CDC13 + DMSO-d6), 2 8(d. 2H), 3 65(s, 3H), 4 3-4 7(m. IH),
505(s, 2H), 6 7 - 7 1 (br, 2H), 73(s, 5H), 7~-8 l(m, 1H), I0 I(s, 1H), ms m/z 323 (M+) The
bicarbonate extract was adjusted to pH = 3 (2N H2SOa), saturated with NaCI, extracted wtth EtOAc
(3x30 mL), dried, evaporated, treated wtth etheral chazomethane, evaporated and chromatographed on
SlhCa gel Elutmn with PhH.EtOAc (7 3) afforded 25% of Z-Asp-du OMe
Brederlck, H, Gompper, R, Schuh, H.G V. Theihg, G. "Neurere Methoden der Preparatwen Orgams-
chen Chemie", Verlag Chem~e, Vol III, p. 163
We are grateful to Professor
D Balasubramaman, Centre for Cellular and Molecular Bmlog2,
Hyderabad, India, for sharing has f'mdings on eye lens protein detenoratmn.
So far, we have been unable to generate a test system to show the cross lmkmg revolving the (o-amino
group of lysme and side chain oxadataon products of hastidme present, however effo~s m thts directmn
are continuing
10
The amino acid, N°-carbamoyt asparagme, arising from de-protectaon of ~), ts structurally similar
to the insecticidal
and nitrogen storing non--coded plant ammo
acid L-alibtzzme
(NI3-carbamoyl-~3-ammo alamne) and has potentaal as
a
competmve antagomst of asparagme
(Rosenthal, G A "Plant Nonprotein Ammo and In-uno Acids", Academic Press, 1982, p 197)
(Received in UK 19 July 1991)