High-throughput synthesis of substituted hydrazine derivatives

Article abstract of DOI:10.3987/COM-07-S(U)14

Regioselective alkylations of the hydrazine derivatives are achieved by using the (2,6-dichloro-4-methoxyphenyl)(2,4-dichlorophenyl)methoxycarboxyl resin. High-throughput synthesis of monosubstituted and 1,1-disubstituted hydrazine building blocks is desc

Full text of DOI:10.3987/COM-07-S(U)14

HETEROCYCLES, Vol. 73, 2007
169
HETEROCYCLES, Vol. 73, 2007, pp. 169 - 175. © The Japan Institute of Heterocyclic Chemistry
Received, 11th June, 2007, Accepted, 2nd August, 2007, Published online, 3rd August, 2007. COM-07-S(U)14
HIGH-THROUGHPUT SYNTHESIS OF SUBSTITUTED HYDRAZINE
DERIVATIVES
Michio Kurosu,* Prabagaran Narayanasamy, and Dean C. Crick
This paper is dedicated to the memory of Professor Ivar Ugi, an inspirational
scientist.
Department of Microbiology, Immunology, and Pathology, College of Veterinary
Medicine and Biomedical Sciences, Colorado State University, 1682 Campus
Delivery, Fort Collins, CO 80523-1682, USA.
E-mail:
michio.kurosu@colostate.edu
Abstract – Regioselective alkylations of the hydrazine derivatives are achieved by
using the (2,6-dichloro-4-methoxyphenyl)(2,4-dichlorophenyl)methoxycarboxyl
resin. High-throughput synthesis of monosubstituted and 1,1-disubstituted
hydrazine building blocks is described.
We recently validated that MenA (1,4-dihydroxy-2-naphthoate prenyltransferase),1 the sixth enzyme in
menaquinone biosynthesis, is a novel target for the development of new drug leads for MDR Gram-positive
pathogens.2 In the discovery of MenA inhibitors, we have generated a library of molecules based on the
4-alkoxydiphenylmethanones which contain tertiary, secondary amines and hydrazines and the library of
molecules was evaluated in an enzymatic assay in vitro (IC50) against MenA, and bacterial growth assays
(MIC).3 From these synthesis-assay processes it was found that the structure of hydrazine significantly
influences MenA and bacterial growth inhibitory activities. Thus, in an attempt to deliver target-specific
library for the development of MenA inhibitors, it is indispensable to diversify the library structure with a
variety of hydrazine building blocks. However, generation of such a library has been limited by the lack of
availability of diverse structures of hydrazine molecules4 from commercial sources.
Several synthetic methods for monoalkylations of the hydrazines using urethane or phthaloyl protecting
group were independently reported by Jamart-Grégoire and Ragnarsson.5 Recently Mäeorg extensively
studied on alkylations of PhNHNHBoc with nBuLi.6 Although these methods are useful for alkylations of
the specific substrates, their procedures involve multiple steps for protection and deprotection or require

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HETEROCYCLES, Vol. 73, 2007
carefully controlled amount of reagents and temperatures. To date, no high-throughput synthesis of
substituted hydrazine derivatives have been reported.7
To efficiently perform selective alkylations of functionalized hydrazines on polymer-support, we devised a
protecting group for hydrazine nitrogen that 1) can be cleaved by a volatile and mild acid such as TFA, 2)
has stability to relatively strong bases, and 3) create a sterically encumbered environment which prevents
overalkylations of the protected Nβ atom of hydrazine unit. In addition, such a protecting group should be
easily grafted onto a polymer-support by a reliable chemical transformation.
We
have
identified
that
the
(2,6-dichloro-4-methoxyphenyl)(2,4-dichlorophenyl)methyl
hydrazinecarboxylate derivative 5b (Scheme 1), conveniently synthesized by Friedel-Crafts reactions
followed by NaBH4 reduction, and CDI-mediated urethane formation reactions, showed an unusual
stability to acids such as 10~15% TFA, 30% HF, 2N HCl, HBr/AcOH, TiCl4, ZnCl2, AlCl3, B(C6F5)3, BCl3,
BBr3, TMSOTf, and La(OTf)3 at rt, bases such as 40% NH4OH, 10% LiOH, 6N NaOH, TlOEt, and DBU at
o
rt, and nucleophiles such as primary and secondary amines at 80 C, and NH2NH2 at rt. However, The
urethane 5b could conveniently be deprotected by using 20% TFA in CH2Cl2 to afford hydrazine•TFA salt
and (2,6-dichloro-4-methoxyphenyl)(2,4-dichlorophenyl)methyl 2,2,2-trifluoroacetate in quantitative
yields.
Cl
Cl
Cl
O
Cl
O
Cl
H
Cl
Me
OH
Cl
O
NaBH4 / MeOH
Cl
2
Me
AlCl3 / PhNO2
80%
Me
Cl
Cl
O
Cl
Cl
Cl
O
95%
1
3
4
CDI
/ CH2Cl2
Cl
NHR
CH3
N
Cl
HN
O
O
N
O
Cl
Cl
HN
Cl
O
H
Cl
RNHNH2
Cl
O
H
O
H
Cl
β
Boc
N
O
α
Me
H
Me
Cl
Cl
O
Cl
Cl
O
80~95%
5a
5a: R = Boc
5b: R = H
recemic mixture
Scheme 1. Synthesis of (2,6-dichloro-4-methoxyphenyl)(2,4-dichlorophenyl)methylhydrazine
carboxylate derivatives, 5a and 5b.
We first investigated the reactivity of 5a8 against representative electrophiles such as benzyl bromide, allyl
bromide, alkyl iodide, and methyl 2-chloroacetate in the presence of Cs2CO3 in DMF. In order to determine
the degree of overalkylation at the Nβ position of 5a, a large excess of electrophiles was utilized in all
reactions. Gratifyingly no overalkylations of 5a were observed in the reactions with electrophiles listed in

HETEROCYCLES, Vol. 73, 2007
171
o
Table 1 even at 50 C (for the stable electrophiles). On the other hand, the same reactions with
BocHNNHBoc gave rise to significant amounts of Nα,Nβ-dialkylsubstituted products.
Table 1. Alkylations of 5a with representative electrophiles.
R
NHBoc
HN
NBoc
O
HN
O
Cl
Cl
H
H
Cl
Cl
O
O
electrophiles
Cs2CO3 / DMF
Me
Me
Cl
Cl
Cl
O
Cl
O
5a
6a~e
entry
1
electrophile1
temperature (oC)
50
time (h)2
product
yield (%)3
p-ClPhCH2Br
12
12
12
12
12
6a9
91
92
90
95
604
2
3
4
5
allyl bromide
C8H17I
25
50
5
6b
6c
6d
6e
CH3I
ClCH2CO2Me
50
1 A large excess (10~15 equiv) of electrophile was used. 2 The reaction was completed within 6 h.
3 Isolated yield. 4 The reaction requires a longer time to achieve complete conversion.
Through X-ray analysis of (2,6-dichloro-4-methoxyphenyl)(2,4-dichlorophenyl)methyl acetate and
molecular modeling of 5b,10 the origin of the excellent regioselectivity of alkylations of 5a and stability
against bases, acids, and nucleophiles can be attributed to the following reasons. The dihedral angles
formed by two planar chlorosubstituted-benzenes and by -CO-O- linkage and the ether methine proton are
83.5o and 159.8o, respectively. There must be a significant electronic repulsion between the o-chloro atoms
in two benzene rings. The o-chloro atom in dichlorobenzene locates towards the carbonyl ester plane. Thus,
the chloro atoms at o-positions in two benzenes hinder nucleophilic attacks at the ester carbonyl from both
re- and si-faces. The 3,5-dichloro atoms in the anisole moiety attenuate an electron donating character of
the methoxy group. Therefore, The urethane 5b would exhibit stability against bases, nucleophiles, and
acids. To date, the generation of dianion of the hydrazine dicarboxylates under Cs2CO3 in DMF at 50 oC has
not been reported.6 Thus, the observed Nα,Nβ-dialkylation of BocHNNHBoc could be explained by a
stepwise process. Nevertheless, the generation of anion at the Nβ position or the approach of electrophiles is
prohibited because of the stereoelectronic factors governed by two planar chlorosubstituted-benzenes.
(2,6-Dichloro-4-hydroxyphenyl)(2,4-dichlorophenyl)methanone, which was obtained in ~70% overall
yield by the treatment of the Friedel-Crafts products with sat. HBr in AcOH / water (2:1) followed by
washing the crude solid with CHCl3,11 was converted to the hydroxy-carboxylic acid possessing C6-linker

172
HETEROCYCLES, Vol. 73, 2007
Cl
Cl
O
H
Cl
H2N
Cl
OH
1) HBr / AcOH
2) BrCH2(CH2)5CO2Et
K2CO3 / DMF
DICI, HOBt
iPr2NEt
/ DMF-CH2Cl2
OH
Me
Cl
Cl
O
Cl
Cl
O
6
O
3) NaBH4 / MeOH
4) KOH / aq MeOH
~60% from 1
3
6
(aminomethyl)
polystyrene (PS)
~1.2 mmol/g
R2
R1
N
HN
O
Cl
H
Cl
OH
Cl
H
Cl
O
1) CDI / CH2Cl2
2) BocNHNH2, or
MeNHNH2, or PhNHNH2
NH2NH2 / DMF
H
N
H
N
Cl
Cl
O
6
O
Cl
Cl
O
6
7
O
8a: R1 = H, R2 = Boc
8b: R1 = H, R2 = Me
8c: R1 = H, R2 = Ph
8d: R1 = H, R2 = H
8a~d 0.9~1.2 mmol/g
Scheme 2. The grafting of 6 on the PS resins and the syntheses of the PS-hydrazines.
6 in three steps in 90% overall yield (1. NaBH4 reduction, 2. alkylation with ethyl 7-bromoheptanoate, and
3. saponification reactions). The hydroxy-carboxylic acid 6 could be grafted onto the
i
(aminomethyl)polystylene (~1.2 mmol/g)12 using a reliable coupling condition [DICI, HOBt, Pr2NEt /
DMF-CH2Cl2 (1/1)]. The resins 7 were then converted to the carbonylimidazole linker which exhibited
excellent reactivities against hydrazine and monosubstituted hydrazines including BocNHNH2, MeNHNH2,
and PhNHNH2 to provide 8a~d whose loading yields were determined to be 0.9~1.2 mmol/g by 1H-NMR
analyses of the crude materials, after cleavage from the resins using 20% TFA in CH2Cl2 for 2 h.13
The alkylations observed with 5a in solution were well transferred to the reactions with the resin 8a. As
summarized in Table 213, the reactions of 8a with the substituted benzyl bromides (10~15 eqiv) in DMF in
the presence of Cs2CO3 (5 equiv) at 50 oC for 12 h gave the corresponding monobenzylated hydrazine•TFA
salts 9a~f in good yields, after cleavage from the resins with 20% TFA. Alkylation of 8a with n-octyl iodide
followed by cleavage from the resin afforded 1-octylhydrazine•TFA salt (9g) in excellent yield. Allylation
o
of 8a smoothly underwent at rt ~ 50 C to provide 1-allylhydrazine•TFA salt, after cleavage. In these
reactions, no overalkylations at the Nβ position were observed. Similarly, alkylations of 8b and 8c gave
the corresponding Nα,Nα-dialkylated hydrazine•TFA salts without detectable contamination of by-products
1
in H-NMR spectra. Symmetrical Nα,Nα-dialkylated hydrazine•TFA could also be synthesized with the
resin 8d with excellent yields. It is worthwhile noting that the solvolytic displacement reactions of 9a~r
with TFA provide TFA ester of 7 in near quantitative yield and the alcohol resin 7 can be regenerated by the
treatment with aq. NH4OH in THF-MeOH for 12 h. The regenerated resins could be reused for the synthesis
of 9a without noticeable decrease of yield.

HETEROCYCLES, Vol. 73, 2007
173
Table 2. High-throughput syntheses of monosubstituted and 1,1-disubstituted hydrazine
derivatives.14
R2
R2
R3
R1
N
electrophiles (R-X)
R
N
20% TFA
CH2Cl2
R
N
TFA
NH2
HN
HN
Cs2CO3 / DMF
12 h
1~2 h
9a~r
R3 = H, Me, or Ph
8a: R1 = H, R2 = Boc
8b: R1 = H, R2 = Me
8c: R1 = H, R2 = Ph
8d: R1 = H, R2 = H
entry
1
starting material
electrophile (R)
R3
H
product
yield (%)3
95
8a
p-ClC6H4CH2Br
9a
2
3
8a
8a
8a
8a
8a
8a
8b
8b
8b
8b
8b
8c
8c
8c
8d
8d
8d
p-CF3OC6H4CH2Br
m-FC6H4CH2Br
o-FC6H4CH2Br
p-MeSC6H4CH2Br
allyl bromide
nC8H17I
H
H
H
H
H
H
9b
9c
9d
9e
9f
93
95
92
91
98
92
95
93
92
98
97
92
95
91
94
94
92
4
5
6
7
9g
9h
9i
8
p-ClC6H4CH2Br
p-CF3OC6H4CH2Br
nC8H17I
Me
Me
9
10
11
12
13
14
15
16
17
18
Me
9j
CH3I
Me
9k
9l
allyl bromide
nC8H17I
Me
Ph
9m
9n
9o
9p
9q
9r
allyl bromide
CH3I
Ph
Ph
allyl bromide
C6H5CH2Br
nC8H17I
allyl
C6H5CH2
C8H17
1 A large excess (10~15 equiv) of electrophile and Cs2CO3 (5 equiv) were used. 2 The reaction was completed
within 6 h. 3 Isolated yield. 4 The reaction requires a longer time to achieve complete conversion.
In conclusion, we have developed a high-throughput synthesis of mono and disubstituted hydrazine
derivative
using
the
tetrachlorodiphenylmethoxycarbonyl
linker.
The
(2,6-dichloro-4-
methoxyphenyl)(2,4-dichlorophenyl)methyl moiety in the hydrazino-urethanes completely blocks the
alkylation at the Nβ position. In addition, the tetrachlorodiphenylmethoxycarbonyl linker developed here is
stable to a wide variety of bases and can be cleaved under a mild condition (20% TFA). Thus,
monosubstituted and 1,1-disubstituted hydrazines can be reliably synthesized with high yield and purity.
Because monosubstituted and 1,1-disubstituted hydrazines are important building blocks for the generation

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HETEROCYCLES, Vol. 73, 2007
of active MenA inhibitors, we have demonstrated the syntheses of specific structure of hydrazine
derivatives as summarized in Table 2. However, tert-butyl 2-alkylhydrazinecarboxylates (i.e.
o
BocHNNHMe) were loaded onto the tetrachlorodiphenylmethoxycarbonyl linker at 50 C and the Boc
group could be removed selectively by using 15% TsOH•H2O in THF-CH2Cl2 (1/1).13 Thus, the method
described here may be applicable to the synthesis of 1,2-disubstituted and 1,1,2-trisubstituted hydrazine
derivatives in a high-throughput manner. Generation of library molecules using the hydrazine building
blocks synthesized by the described method and evaluation of these molecules against MenA and MDR
Gram-positive bacteria will be reported elsewhere.
ACKNOWLEDGEMENTS
We thank the National Institutes of Health (NIAID grants AI049151, AI018357, and AI06357) and
Colorado State University for generous financial support. Mass spectra were obtained on instruments
supported by the NIH Shared Instrumentation Grant GM49631.
REFERENCES AND NOTES
1. K. D. Suvana, R. Stevenson, R. Meganathan, and M. E. S. Hudspeth, J. Bacteriol., 1998, 180, 2782.
2. M. Kurosu and D. C. Crick, Compositions and Methods of Use of Electron Transport System
Inhibitors Serial Number: PCT / US2007 / 63122.
3. M. Kurosu, P. Narayanasamy, K. Biswas, R. Dhiman, and D. C. Crick, J. Med. Chem., 2007 in press.
4. For a recent report on the alkylation of protected hydrazines, see: L. K. Rasmussen, J. Org. Chem.,
2007, 71, 3627; J. Barluenga, P. Moriel, F. Aznar, and C. Valdés, Org. Lett., 2007, 9, 275 and
references therein. For a review, see: A. Zergra, Curr. Med. Chem., 2005, 12, 589.
5. N. Brosse, M. F. Pinto, J. Bodiguel, and B. Jamart-Grégorire, J. Org. Chem., 2001, 66, 2869; O.
Tśubrik and U. Mäeorg, Org. Lett., 2001, 3, 2297; N. Brosse, M. F. Pinto, and B. Jamart-Grégorire, J.
Org. Chem., 2000, 65, 4370; U. Mäeorg and U. Ragnarsson, Tetrahedron Lett., 1998, 39, 681.
6. A. Bredihhin, U. M. Groth, and U. Mäeorg, Org. Lett., 2007, 9, 1097.
7. N-Amination reactions have been widely demonstrated in the synthesis of 1,1-disubstituded
hydrazines, see: U. Ragnarson, Chem. Soc. Rev., 2001, 30, 205.
1
8. Data for 5a: H-NMR (CDCl3, 300 MHz): δ 7.55 (s, 1H), 7.37 (m, 1H), 7.26 (m, 2H), 6.88 (s, 2H),
6.34 (bs, 1H ), 6.31 (bs, 1H), 3.81 (s, 3H), 1.46 (s, 9H).; 13C-NMR (CDCl3, 100 MHz): 159.9, 155.3,
136.9, 130.5, 129.7, 126.5, 124.3, 115.3, 81.3, 72.4, 55.8, 28.1.; IR (neat, cm-1): 3583, 2919, 2362,
1652, 1558. LRMS (ESI) C20H21N2O5Cl4 (M+H+) 509.0.
9. Data for 6a: 1H-NMR (CDCl3, 300 MHz): δ 7.56 (s, 1H), 7.25 (m, 7H), 6.88 (s, 2H), 6.36 (bs, 1H ),

HETEROCYCLES, Vol. 73, 2007
175
13
4.72 (m, 2H), 3.81 (s, 3H), 1.42 (s, 9H).; C-NMR (CDCl3, 100 MHz): 159.9, 154.9, 154.2, 137.0,
134.7, 134.2, 133.7, 130.6, 130.1, 129.5, 128.7, 126.4, 124.3, 115.2, 81.7, 72.8, 55.7, 52.9, 28.0.; IR
(neat, cm-1): 3583, 2919, 2367, 1652, 1558, 1540.; LRMS (ESI) C27H26N2O5Cl5 (M+H+) 633.4.
10. A SPARTAN conformational search by semiempirical calculation using AM1 basis set indicate that
lowest energy conformation of (2,6-dichloro-4-methoxyphenyl)(2,4-dichlorophenyl)methoxy
carbonyl moiety of 5b was well in agreement with that of X-ray structure of
(2,6-dichloro-4-methoxyphenyl)(2,4-dichlorophenyl)methyl acetate.
11. (2,6-Dichloro-4-hydroxyphenyl)(2,4-dichlorophenyl)methanone showed very poor solubility against
CHCl3, hexanes, and Et2O, but dissolved in MeOH. Thus, this compound could be isolated without
using chromatographic purification.
12. Purchased from Aldrich.
13. M. Kurosu, K. Biswas, and D. C. Crick, Org. Lett., 2007, 9, 1141.
14. The following example represents typical experimental procedure: The resins 8a (100 mg, 0.1 mmol)
in DMF (1 mL) was added Cs2CO3 (162.5 mg, 0.5 mmol) and p-ClC6H4CH2Br (204 mg, 1.0 mmol).
o
The reaction mixture was gently stirred at 50 C for 12 h. The resins were washed with DMF,
THF-water (3/1), THF, and EtOAc, and dried under high vacuum. The resins were suspended in
CH2Cl2 (1 mL) and TFA (~0.2 mL) was added. After 1 h the resins were filtered and washed with
o
CH2Cl2. The combined CH2Cl2 solution was evaporated at 30~40 C and dried under high vacuum.
1H-NMR spectroscopy was applied to the analysis of the crude product using
1-bromo-4-methoxybenzene as an internal standard.