Baran Lab
•
•
Bernhard Witkop
born 1917 in Freiburg, Germany
studied Chemistry in Munich till 1938
(diploma), 1940 (PhD)
1938-1946 private assistent of Prof. Wieland
1948-1950 lecturer at the Havard University
US citizenship in 1953
from 1957 Chief of the Laboratory of
Chemistry, National Institute of Arthritis and
Metabolic Diseases, Bethesda, MD
his research interests were versatile,
isolation of natural products, reaction
mechanisms, synthetic organic chemistry,
and biochemistry
more than 300 publications, many of them in
J. Am. Chem. Soc.
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•
M. Maue
Biochemistry - NIH-Shift1
expected reaction
NH2
NH2
OH
OH
O2, 2H+
phenylalaninehydroxylase
O
T
O
THO
radioactive
OH
observed reactions
NH2
NH2
OH
O
OH
O2, 2H+
O
phenylalaninehydroxylase
T
T
OH
NHAc
>90%
NHAc
O2, 2H+
phenylalaninehydroxylase
T
T
OH
>4-5%
mechanism?
1
G. Gruoff, J. W. Daly, D. M. Jerina, J. Renson, B. Witkop, S. Udenfriend, Science 1967, 157, 1524-1530.
1
Bernhard Witkop
Baran Lab
M. Maue
Biochemistry- protein structure2
•
Enzymatic and non-ezymatic pathways to
cleave amide bonds selectively were
important to determine the primary
sequence and the reactive center of
enzymes
•
•
NBS in 8.0 M urea cleaves amide bonds
next to tryptophanes
NHR
RHN
N
H
N
H
RHN
R
N
H
RHN
RHN
NHR
O
- MeSCN
NHR hydrolysis
•
hydrolysis
O
- RNH2
O
O
N
H
•
No side reactions with tyrosine or other
aromatic amino acids
•
interesting reaction at pH above pH 9
O
RHN
O
O
N
H
N
RHN
O
S
S
O
O
NHR
O
Br-CN
NHR
Br
NHR NBS
O
H2O, O2
cyanogen bromide cleaves the amide bound
next to methionine
O
NHR
R-NH2
R
Only a slow reaction with cysteine, no
reaction with all the other amino acids
NHAc NBS
R
R
NHAc base
Br
NAc
N
H
2
B. Witkop, Science 1968, 162, 318-326.
N
N
H
2
Bernhard Witkop
Baran Lab
M. Maue
Isolation and determination of Natural Products
structure of yohimbine3
N
H H
N
N
H H
N
∗
∗
20
15
∗
Tl2O
N
H
∗
20
15
OH OH
•
•
•
3
∗
Pt/H2
OH
N
•
∗
O
O
O
N
The general structure was known, but
not the absolute stereo-chemistry of
the stereocenters at C15 and C20
treatment of erectile dysfunction
Increaes blood flow in extremeties
many side affects!! (high blood
pressure, anxiety….)
B. Witkop, J. Am. Chem. Soc. 1949, 71, 2559-2566.
∗ ∗
H
H
MeI
N
H
N
∗
∗
• by comparison of IR-data and
optical activity of synthetic and the
isolated decahydro-isoquinoline
they could figure out the absolute
stereo-chemistry of C15 and C20
3
Bernhard Witkop
Baran Lab
M. Maue
Photochemistry
Chemistry with thymine dimers4
O
O
NH
HN
O
O
N
H
N
H
O
hν
O
MeMe
NH
HN
O
Photochemistry also with
3-deazapyrimidone5
N
N
RH HR
O
O
O
O
+3 separable isomers
hν
O
N
H
N
H
O
O
MeMe
HN
H2N
O
O
hν
NH
NH2
O
N
N
CH2
easy access to highly substituted
diastereomerically pure cyclobutanes
4
5
O
OH
H H
O O
T. Kunieda, B. Witkop, J. Am. Chem. Soc. 1971, 93, 3493-3499.
B. Witkop et al., Lieb. Ann. Chem. 1988, 979-981.
N
N
RH HR
O
+ 3 separable isomers
NaBH4
HO
O
MeMe
n
n =1-3
O
O
N
O
MeMe
H H
CH2
N
O
n
only the cis-syn isomer
4
Bernhard Witkop
Photochemistry – cage compounds6
Baran Lab
M. Maue
H
N
NH
HO
EtOH-H2O
∆T, hν
-HCl
O
H
N
HO
O
HO
1, 5% O
Cl
O
EtOH-H2O
∆T, hν
O
HN
H
N
NH
O
O
2, 40%
O
HN
NH
O
O
O
O
O
Mechanism?
Cl
O
O
O
3, 12%
6 1
NH
6
5
4 1
3
HN
5
NH
2
4
HO
O
3
O
2
[4+2]
O
3
Norrish type I
2
[2+2]
HN
O
6
B. Witkop et al., J. Am. Chem. Soc. 1974, 96, 2564-2569.
O
4 2
3 3
6
5
5
1 2
4
1
O
6
NH
5
Bernhard Witkop
Baran Lab
M. Maue
Photochemistry
Stereochemistry of photocyclisations
with heterocyclic anilides7
hν
NH
S
O
H
H
S
Photooxidation of Trp to kynurenine8
COOH O2, hν
Rose Bengal
NH2
H
NH
NH
O
N
H
S H O
NMe
S
O
H
H
S
H
O
hydrolysis
COOH
O
N
H
N
S H O
OH
COOH
NH2
NMe
NMe
NH2
O
NHCHO
O2*
HOO
hν
COOH
NH
Cl
Explain the different mechanisms leading
to the cis and the trans product!?
Cl
Cl
ONa
Cl
O
I
NaO
O
I
O
Rose Bengal
7
8
B. Witkop et al., J. Org. Chem. 1975, 40, 3001-3003.
B. Witkop et al., Proc. Natl. Acad. Sci. 1977, 4730-4732.
6
Bernhard Witkop
Baran Lab
M. Maue
Synthesis and Mechanisms
Living on the edge….9
Fischer indole synthesis in
polyphosphoric acid10
1) tetranitromethane
2) Na2S2O4
N
H
N
N
H
mechanism?
O
NH2
NH polyphosphoric acid
>100 °C
NO2
tetranitromethane
C(NO2)3-
N
H
N
H
Me
NO2
NH2
N
H
Me
Na2S2O4
N
H
NH2
NO2
NO2
NO2
-NH3
Me
9
10
70%
Good yields, easy workup
Limitation: only the synthesis of 2substitued indoles possible
NO2
C NH
N
H
H
N
-HNO2
CN
N
H
B. Witkop et al., J. Am. Chem. Soc. 1969, 91, 6199-6200.
B. Witkop et al., J. Am. Chem. Soc. 1952, 74, 3948-3949.
7
Baran Lab
Bernhard Witkop
M. Maue
Synthesis and Mechanisms - Chemistry of Spirooxindoles
11
J. B. Patrick, B. Witkop, J. Am. Chem. Soc. 1952, 75, 2572-2576.
8
Bernhard Witkop
Baran Lab
M. Maue
Synthesis and Mechanisms -Twofold Wagner-Meerwein-Rearangments12-13
Expected reaction with Lithiumorganyl
O
HO
RLi
N
H
R
R
N
N
H
PhMgBr
N
H
H
O
O
Ph
Ph
Ph
N O
H
H
O
OMgX2-
X2MgO
MgX2
RMgX
N
H
-
LA
Ph
N
H Ph
Ph
Ph
OLA
N
RMgX
O
-LA
O LA
N
MgX
Ph
N
H
LA
Ph
N
H
Ph
O
Unexpected reaction with Grignard reagent
Ph
N
H Ph
N O
H
H
O
-H2O
N
H
N
H
O
Ph
Ph
R
H+
R
H
O
Ph
N
H Ph
N
H Ph
OLA
N Ph
H
-
X2MgO
N
12
13
R
Rearangement can be induced by an
excess Grignard reagent, acid or BF3OEt2
N
R
XMg
J. B. Patrick, B. Witkop, J. Am. Chem. Soc. 1951, 73, 1558-1564.
A. Ek, B. Witkop, J. Am. Chem. Soc. 1951, 73, 5664-5669.
9
O
Bernhard Witkop
Baran Lab
M. Maue
Synthesis and Mechanisms
Deketopiperazines of 3,4-dehydroproline – unique structural properties14
H O
N
H
HCl
OH
SOCl2
MeOH
H O
N
H
HCl
H O
NEt3
N
OMe
O H
N
H O
N
N
O H
either D,D- or L,L-diketopiperazines
Stereodiagram of the L,L-diketopiperazine
14
B. Witkop et al., J. Am. Chem. Soc. 1972, 96, 539-543.
10
Bernhard Witkop
Baran Lab
M. Maue
Synthesis and Mechanisms
Batrachotoxin15
• a cardiotoxic alkaloid from the colombian
arrow poison frog Phyllobates aurotaenia
(LD50 = 2µg/kg mice)
• very labil venom (4 expeditions to Colombia
were necessary) and most of the experiments
were carried out in µg-quantities
OR
OH
HO
Me
HO
Me
N
• ultimate proof of their hypothesis was the partial
synthesis of Batrachotoxine from Batrachotoxine
A and activated 2,4-dimethylpyrrole-3-carboxylic
acid
OH
HO
Me
O
HO
Me
O
HO
O
O
O
HO
Batrachotoxin A
known structure
O
Batrachotoxine
HN
O
HO
HO
N
O
O O H
N
EtO O
N
HO
Me
Batrachotoxin
unknown residue R
O
HO
N
O
derivative with fully substituted pyrrol
more stable and twice as toxic as Batrachotoxine
• by NMR, UV/Vis and MS they found that R
is 2,4-dimethylpyrrole-3-carboxylic acid
12
HN
O
N
O
O
O
O O H
N
EtO O
T. Tokuyama, J. Daly, B. Witkop, J. Am. Chem. Soc. 1969, 91, 3931-3938.
11