DOI: 10.1002/cmdc.201600108
Communications
Synthesis and Biological Evaluation of N2-Substituted 2,4-
Diamino-6-cyclohexylmethoxy-5-nitrosopyrimidines and
Related 5-Cyano-NNO-azoxy Derivatives as Cyclin-
Dependent Kinase 2 (CDK2) Inhibitors
Daniela Cortese,[a] Konstantin Chegaev,[a] Stefano Guglielmo,[a] Lan Z. Wang,[b]
The potent and selective cyclin-dependent kinase 2 (CDK2) in-
hibitor NU6027 (6-cyclohexylmethoxy-5-nitroso-2,4-diaminopyr-
imidine) was used as the lead for the synthesis of a series of
analogues in order to provide further insight into the struc-
ture–activity relationships for 2,4-diaminopyrimidine CDK2 in-
hibitors. Aliphatic amino substituents were introduced at posi-
tion 2. The use of linear or less sterically hindered amines gave
rise to compounds endowed with slightly better activity than
the lead; on the other hand, the compounds were less active if
a bulkier amino substituent was used. Substitution of the 5-ni-
troso group with a 5-cyano-NNO-azoxy moiety afforded a new
class of inhibitors, the activity of which against CDK2 was
found to be similar to that of the nitroso series. The most
active nitroso compound was 8b ((2S)-2-[(4-amino-6-cyclohex-
these inhibitors, an interesting type is represented by 2,4-dia-
mino-6-cyclohexylmethoxy-5-nitrosopyrimidine (1, NU6027)
(Figure 1), a competitive inhibitor of CDK1 and CDK2 isoforms
Figure 1. Reference compounds 1–3.
with respect to ATP (CDK2 IC50 =2.2 mm).[3–5] Owing to the in-
tramolecular hydrogen bond between the adjacent 5-nitroso
and 4-amino groups, this compound assumes a pseudo-purine
geometry, which is reminiscent of the structure of 6-(cyclohex-
ylmethoxy)-9H-purine (2, NU2058; Figure 1), an early relatively
potent CDK1 and CDK2 inhibitor (CDK2 Ki =12 mm).[6] Com-
pound 1 can interact with the ATP binding site of the enzymes
by a triplet of hydrogen bonds (for CDK2: 2-NH2 to Leu83 (CO),
N3 to Leu83 (NH), 4-NH2 to Glu81 (CO)).[4] These interactions
exactly reproduce those of 2. An extended series of analogues
of 1 modified at the 2-, 5- and 6-position(s) were synthesized
in order to shed light on the structure–activity relationships
(SARs) in this lead compound.[3,4] In a recent paper we de-
scribed a new pyrimidine scaffold, the 2,4-diamino-5-(cyano-
NNO-azoxy)-6-(cyclohexylmethoxy)pyrimidine (3; Figure 1), en-
dowed with potent CDK2 inhibitory activity.[7] This substance
can be formally obtained by substitution of the nitroso group
of 1 with the cyano-NNO-azoxy moiety, which is present in the
antibiotic “calvatic acid” (4-[(Z)-cyano-NNO-azoxy]benzoic acid)
initially isolated from the culture broth of Calvatia lilacina.[8]
This unusual functional group has been used to design several
bioactive compounds, such as antimicrobial and antitumor
agents, enzyme inhibitors, and calcium channel blockers.[9–13]
The cyano-NNO-azoxy moiety displays an electron-withdrawing
property very similar to that of the nitroso group (spNO =0.91,
spONNCN =0.89), whereas it is endowed with different lipophilici-
ty (pNO =À1.20, pONNCN =À0.26) and steric properties.[14,15]
A molecular modeling study has suggested a role for a con-
served water molecule in stabilizing the bioactive pose of 3 in
its interaction with the ATP binding site of the enzyme. Prelimi-
nary SARs showed that the substitution of the cyano group of
ylmethoxy-5-nitrosopyrimidin-2-yl)amino]propan-1-ol;
IC50 =
0.16 mm), while in the 5-cyano-NNO-azoxy series the most
active compound was 9b (4-amino-5-[(Z)-cyano-NNO-azoxy]-2-
{[(2S)-1-hydroxypropan-2-yl]amino}-6-cyclohexylmethoxypyrimi-
dine; IC50 =0.30 mm). Taken together, these new analogues of
NU6027 enhance our understanding of the structure–activity
relationships for 2,4-diaminopyrimidine CDK2 inhibitors.
Cyclin-dependent kinases (CDKs) are serine/threonine kinases
that display abnormal activity in many kinds of tumors.[1] This
family of kinases is represented by eleven members (CDK1–
CDK11) and related cyclins.[2] Today, there is a great interest in
small-molecule CDK inhibitors as potential anticancer drugs.
Over the past decade, many such compounds belonging to
different chemical classes have been developed.[3] Among
[a] Dr. D. Cortese, Dr. K. Chegaev, Dr. S. Guglielmo, Prof. R. Fruttero
Department of Drug Science and Technology,
Universitꢀ degli Studi di Torino, Via P. Giuria 9, 10125 Turin (Italy)
[b] L. Z. Wang
Northern Institute for Cancer Research, Paul O’Gorman Building,
Medical School, Newcastle University,
Framlington Place, Newcastle Upon Tyne, NE24HH (UK)
[c] Prof. B. T. Golding, Dr. C. Cano
Northern Institute for Cancer Research, Bedson Building,
School of Chemistry, Newcastle University,
Newcastle Upon Tyne, NE17RU (UK)
Supporting information and the ORCID identification number(s) for the
ChemMedChem 2016, 11, 1 – 5
1
ꢁ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
These are not the final page numbers! ÞÞ