Parallel solution-phase synthesis of an adenosine antibiotic analog library

Article abstract of DOI:10.1021/co300127z

A library of eighty one adenosine antibiotic analogs was prepared under the Pilot Scale Library Program of the NIH Roadmap initiative from 5′-amino-5′-deoxy-2′,3′-O-isopropylidene-adenosine 3. Diverse aldehyde, sulfonyl chloride and carboxylic acid reactant sets were condensed to 3, in solution-phase fashion, leading after acid-mediated hydrolysis to the targeted compounds in good yields and high purity. No marked antituberculosis or anticancer activity was noted on preliminary cellular testing, but these nucleoside analogs should be useful candidates for other types of biological activity.

Full text of DOI:10.1021/co300127z

Research Article
pubs.acs.org/acscombsci
Parallel Solution-Phase Synthesis of an Adenosine Antibiotic Analog
Library
Omar Moukha-chafiq* and Robert C. Reynolds†
Southern Research Institute, Drug Discovery Division, Birmingham, Al 35205
S
* Supporting Information
ABSTRACT: A library of eighty one adenosine antibiotic analogs was pre-
pared under the Pilot Scale Library Program of the NIH Roadmap initiative
from 5′-amino-5′-deoxy-2′,3′-O-isopropylidene-adenosine 3. Diverse aldehyde,
sulfonyl chloride and carboxylic acid reactant sets were condensed to 3, in
solution-phase fashion, leading after acid-mediated hydrolysis to the targeted
compounds in good yields and high purity. No marked antituberculosis or
anticancer activity was noted on preliminary cellular testing, but these
nucleoside analogs should be useful candidates for other types of biological activity.
KEYWORDS: 5′-amino, carboxamide and sulfonyl-adenosine antibiotic analogs
cell-free protein synthesis.37 Hence, the 5′-amino group of the
INTRODUCTION
■
nucleoside ribose moiety was chosen as a site of diversification
Historically, nucleoside chemistry has primarily focused on low
through robust peptidyl chemistry in order to prepare the target
throughput production and screening of analogs for anticancer,
library of 5′-amido derivatives 4−34 (Scheme 1). The resulting
nucleoside peptide library was expected to show reasonable
stability to dissolution, storage and screening as evidenced for
similar aminoacyl functions found in various nucleoside anti-
biotics, such as puromycin, gougerotin, amicetin, and blasticidin S,
all known inhibitors of protein synthesis. Thus, 3 was
synthesized in two steps (Scheme 1) starting from 2′,3′-O-
isopropylidene adenosine 1, which was reacted with triphenyl-
phosphine, 1,3-dihydro-1,3-dioxo-2H-isoindole and diisopropyl
azodicarboxylate to give 5′-deoxy-5′-(1,3-dihydro-l,3-dioxo-2H-
isoindol-2-y1)-2′,3′-O-isopropylidene adenosine 2. Hydrazinol-
ysis of 2 with hydrazine monohydrate in ethanol gave 3 in 78%
yield according to the previously reported method.19
To achieve our targeted 5′-amido compounds 4−34 (Figure 1),
we explored several methods for peptide coupling of 3 to
diverse and readily available carboxylic acid-substituted or
N-tert-butyloxycarbonyl (Boc) amino acid derivatives using
2-(1H-benzotriazol-1-yl)-1,1,3,3-tetramethyluronium hexafluoro-
phosphate (HBTU) and N,N′-dicyclohexylcarbodiimide
(DCC). HATU [(2-(7-Aza-1H-benzotriazole-1-yl)-1,1,3,3-tetra-
methyluronium hexafluorophosphate] has been reported to
rapidly provide the peptide linkage in high yield and with little
or no racemization. In our hands, the best results were obtained
with HATU (1 equiv) and N,N-diisoproplyethylamine (DIEA,
1.5 equiv) in acetonitrile for 30−180 min. The utility of HATU
allowed the facile preparation of the title compounds with a
variety substituents and ready adaptation to a parallel format
using a Radleys 12-place carousel reaction station on a 0.5 mmol
scale. Subsequent acid-mediated deprotection of the acetonide
antifungal, and antiviral antimetabolite activities.1−8 Beyond the
traditional nucleosides with an available 5′-hydroxyl that can
enter nucleoside metabolic pathways, there are numerous examples
of relatively simple to complex nucleoside antibiotics that
exhibit diverse alternative mechanisms of action.9,10 Natural
nucleoside antibiotics, for example, demonstrate potent
activities, such as protein synthesis inhibition, glycosyltransfer-
ase inhibition, and methyltransferase inhibition, among
others.9−13 More recently, there has been a trend to develop
approaches for the synthesis and screening of this class of
compounds, which do not exhibit typical antimetabolite
activities based on nucleoside phosphorylation and incorpo-
ration into nucleoside metabolic pathways.14−18 In many
respects, the nucleoside scaffolds offer an opportunity for
numerous diverse and directionally oriented substitutions to
probe for activity against diverse protein binding sites. Further-
more, many of these basic scaffolds are not well represented in
commercial chemical space, including the Molecular Library
Small Molecule Repository (MLSMR) [see PubChem Sub-
stance at http://www.ncbi.nlm.nih.gov/pcsubstance]. Hence,
we have designed and prepared nucleoside antibiotic-like small
molecule libraries under the Pilot Scale Library Program of the
NIH Roadmap Initiative to probe specific or general biological
activities. We report herein the initial phase of this project
which is the synthesis of a library of eighty one 5′-amido-,
amino-, and sulfonylamido-adenosine analogs derived from 5′-
amino-5′-deoxy-2′,3′-O-isopropylidene-adenosine 3 (Scheme 1)
using parallel solution phase chemistry.
Both 3 or its analog 5′-amino-5′-deoxy-adenosine are suitable
precursors for the synthesis of a variety of biologically active
nucleoside analogs19−36 dating back to the first report describ-
ing the synthesis of 5′-amino-5′-deoxy-5′-N-aminoacyl peptide
derivatives of guanosine, and adenosine and their effects on
Received: October 23, 2012
Revised: January 15, 2013
© XXXX American Chemical Society
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Research Article
a
Scheme 1
a
Reagents and conditions: (i) phthalamide, PPh3, DIAD; (ii) H2NNH2, EtOH; (iii) R = a part from N-Boc amino acid, HATU, DIEA, CH3CN;
R = a part from an aldehyde, MeOH, molecular sieves, 0−40 °C, NaBH4; R = a part from sulfonyl chloride, DMF, CsCO3; (iv) 50% formic acid, 70 °C.
Figure 1. Structures of compounds 4−34.
as well as the Boc protecting group using 50% formic acid,
again in a parallel format, furnished the desired compounds
4−34 in quantitative yields and high purity.
Next, we prepared a diverse small library of 5′-N-alkyl-
5′-deoxy-adenosine derivatives 35−67 (Figure 2) based upon
the important biological activity and stability exhibited by
B
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Figure 2. Structures of compounds 35−67.
Figure 3. Structures of compounds 68−84.
known natural analogues. Reductive amination is an efficient
method that is readily adaptable to parallel format and, hence,
we adapted this reaction to couple compound 3 with thirty
three commercially available aldehydes. Successful couplings
were achieved in methanol in the presence of molecular sieves
to efficiently drive intermediate imine formation. It must be
noted that the use of molecular sieves was crucial in terms of
yield improvement and reaction time. The reaction was also
readily adapted to a parallel format on a Radleys 12-place
carousel reaction station at room temperature, although
occasionally reactions were facilitated with less soluble
aldehydes by warming for the first ten minutes at 40 °C.
C
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The resulting aldimines were carefully treated in situ with solid
sodium borohydride for one-half hour and the reaction was
then preadsorbed and dried on silica gel without further workup
followed by flash chromatography purification. Similarly, the
hydrolysis of the isopropylidene blocking groups of the
resulting intermediates using 50% formic acid was successful
leading to the desired targets 35−67 in quantitative yields.
The synthesis of sulfonylamide adenosine analogs 68−84
(Figure 3) was achieved by reacting intermediate 3 with
seventeen commercially available sulfonyl chlorides. The
reactions were carried out in N,N-dimethylformamide (DMF)
at room temperature using cesium carbonate as base followed
by hydrolysis of the isopropylidene blocking groups as
described above.
(HT29 colon, PC3 prostate, and MDA-MB-231 breast). Only
compounds 39, 42, and 43 showed toxicity at less than 50 μM
in these cells as shown in Table 1 (details of these biological
studies are provided in Supporting Information).
All the prepared analogs have been submitted (20 mg) in the
Molecular Libraries Small Molecule Repository (MLSMR) to
be screened against a wide range of biological assays (see www.
ncbi.nlm.nih.gov/pcsubstance search term Robert Reynolds).
Certain analogs (Figure 4) exhibited interesting activities in
these primary screens. For example, adenosine peptides 9 and
21 were found to be malaria HSP40-mediated yeast toxicity
inhibitors; 16 was identified as an inhibitor of G-Protein
coupled receptor kinase-2 (GRK2) (protein target = beta-
adrenergic receptor kinase 1); 39 was identified as an activator
of methionine sulfoxide reductase A (MsrA); compound 48
was found to be inhibitor of prion protein 5′ UTR mRNA; 58
and 63 were identified as inhibitors of the histone demethylase
GASC-1 (gene amplified in squamous cell carcinoma-1) and
vitamin D receptor (VDR) respectively; sulfonylamide
adenosine compound 71 inhibited the interaction of LANA
1−23 peptide with purified nucleosomes (containing H2A/
H2B histone dimers) while the derivative 74 was found to
inhibit scavenger receptor class B using DiI-HDL.
BIOLOGICAL EVALUATION
■
The described analogs were tested in vitro for their
effectiveness against Mycobacterium tuberculosis (Mtb).38 None
of the compounds showed appreciable activity at compound
concentrations lower than 100 μM. Only compound 42
exhibited slight inhibition with an IC50 of 43 μM. Also, they
were screened in vitro against three human tumor cell lines
Table 1. Effect of Prepared Analogs on Cell Growth
CONCLUSION
■
cancer screen
In conclusion, a small library of eighty one adenosine antibiotic-
like analogs derived from 5′-amino-5′deoxy-2′,3′-O-isopropyli-
deneadenosine was prepared in good yields and high purity
using a parallel solution phase format. No marked anti-
tuberculosis nor anticancer activity was witnessed and all the
prepared analogs have been submitted for screening in the
Molecular Libraries Probe Production Centers Network
(MLPCN), preliminary screening via the MLPCN has
a
a
a
compound
HT29 (CC50) PC3 (CC50) MDA (CC50)
4−38, 40−41, and 44−84
>50
14
9
>50
45
>50
31
39
42
43
24
>50
>50
12
>50
a
CC50 = Concentrations of compound required for 50% growth
inhibition of cancer cells.
Figure 4. Some active adenosine analogues.
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AUTHOR INFORMATION
Corresponding Author
*E-mail: moukhachafiq@southernresearch.org.
■
Present Address
†Department of Chemistry, University of Alabama at
Birmingham, Birmingham, AL 35294
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This investigation was supported by NIH Grant 1P41
GM086163-01 (titled Pilot-Scale Libraries Based on Nucleo-
side Templates for the ML Initiative, Robert C. Reynolds, PI.).
We thank James M. Riordan, Jackie Truss, Mark Richardson,
and David Poon of the Molecular and Spectroscopy Section of
Southern Research Institute for analytical and spectral data.
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