Novel substituted aminoalkylguanidines as potential antihyperglycemic and food intake-reducing agents

Article abstract of DOI:10.1021/jm8001636

We report the synthesis and evaluation of aminoalkylguanidine analogues and derivatives in C57BL/KsJ db/db diabetic mice, following identification by random screening of 1a and 1b as potential antihyperglycemics and/or modulators of food intake. These compounds are related to galegine, a γ,γ- dimethylallylguanidine. Between the newly identified compounds, 1h N-(cyclopropylmethyl)-N′-(4-(aminomethyl)-cyclohexylmethyl)guanidine showed the most balanced activity as antihyperglycemic and food intake-reducing agent.

Full text of DOI:10.1021/jm8001636

J. Med. Chem. 2008, 51, 3073–3076
3073
Novel Substituted Aminoalkylguanidines as
Potential Antihyperglycemic and Food
Intake-Reducing Agents
Emanuela Tassoni,*,† Fabio Giannessi,‡ Tiziana Brunetti,†
Pompeo Pessotto,‡ Michela Renzulli,§
Massimiliano Travagli,§ Suvi Rajamäki,§ Samanta Prati,‡
Secondo Dottori,‡ Federico Corelli,§ Walter Cabri,†
Paolo Carminati, and Maurizio Botta*,§
Figure 1
Chemistry and Analytical Department, Endocrinology and
Metabolism Department, and Director of Research and
DeVelopment Department, Sigma-Tau S.p.A., Via Pontina Km
30.400, 00040 Pomezia, Italy, and Dipartimento Farmaco Chimico
Technologico, UniVersity of Siena, Siena, Italy
Scheme 1a
ReceiVed February 15, 2008
Abstract: We report the synthesis and evaluation of aminoalkylguani-
dine analogues and derivatives in C57BL/KsJ db/db diabetic mice,
following identification by random screening of 1a and 1b as potential
antihyperglycemics and/or modulators of food intake. These compounds
are related to galegine, a γ,γ-dimethylallylguanidine. Between the newly
identified compounds, 1h N-(cyclopropylmethyl)-N′-(4-(aminomethyl)-
cyclohexylmethyl)guanidine showed the most balanced activity as
antihyperglycemic and food intake-reducing agent.
a Reagents and conditions: (a) KOH, Bu4NBr, γ,γ-dimethylallyl bromide,
4-fluorobenzyl bromide or allyl bromide, DCM, MeCN, room temp, 12 h,
100%; (b) hydroxymethylcyclopropane or 3-methyl-1-butanol, PPh3, DIAD,
THF, reflux, 12 h, 95%.
Type 2 diabetes is a growing major global public health
problem, with a currently estimated worldwide incidence of
about 194 million people and expected to increase to 330 million
by 2025.1 Type 2 diabetes is usually due to resistance to insulin,2
arising as a consequence of obesity, sedentary lifestyle, and
aging and resulting in hyperglycemia, blood pressure elevation,
and dyslipidemia. Despite the relatively recent explosion of new
classes of pharmacologic agents,3 the medical need still remains
very high.
Scheme 2a
During our research into new antidiabetic agents, we identi-
fied, by random in vivo screening of several molecules, two
aminoalkylguanidine compounds, 1a and 1b, as antihypergly-
cemic agents and/or food intake modulators in C57BL/KsJ db/
db diabetic mice after subcutaneous treatment. Compound 1b
had previously been investigated as an antihypertensive agent.4
These molecules are aminoalkyl derivatives of galegine
(Figure 1), a γ,γ-dimethylallylguanidine active for the treatment
of type 2 diabetes isolated from the goat’s rue plant (Galega
officinalis).5 An investigation of its derivatives led to the
discovery of metformin,3i,j a biguanidine introduced in the late
1950s and now a very widely used oral antidiabetic agent
(Figure 1).
a Reagents and conditions: (a) suitable amine; (b) Boc-aminoalcohol,
The activity of Galega officinalis on the reduction of food
intake was also reported.6 Compounds 1a and 1b are also
structural analogues of agmatine (Figure 1), a polar metabolite
extracted from the Venezuelan plant Verbesina caracasana.
PPh3, DIAD, THF, reflux, 12 h, 65-70%.
Agmatine and its derivatives have been studied as antihyper-
tensive agents.4
In this paper we report the synthesis of compounds 1a and
1b, together with a series of new analogs, followed by their
evaluation in ViVo in diabetic mice as potential new antidiabetic
and/or food intake modulators.
Compounds 1a-t were synthesized starting either N,N′,N′′-
tris(tert-butoxycarbonyl)guanidine 2a or commercially available
thiourea 2b, which were first alkylated with a suitable halide
or alcohol to give 3a-f (Scheme 1).
* To whom correspondence should be addressed. For E.T.: phone,
+390691393577; fax, +390691393638; e-mail, emanuela.tassoni@sigma-
tau.it. For M.B.: phone, +390577234334; fax, +390577234333; e-mail,
botta@unisi.it.
†
Chemistry and Analytical Department, Sigma-Tau S.p.A.
Endocrinology and Metabolism Department, Sigma-Tau S.p.A.
University of Siena.
‡
§
Director of Research and Development Department, Sigma-Tau S.p.A.
10.1021/jm8001636 CCC: $40.75
2008 American Chemical Society
Published on Web 05/09/2008

3074 Journal of Medicinal Chemistry, 2008, Vol. 51, No. 11
Letters
Scheme 3a
Scheme 6a
a Reagents and conditions: (a) HgCl2, triethylamine, amine, DMF, 4 h,
80%; (b) 6-(N-Boc)amino-1-hexanol or 4-(N-Boc)amino-1-butanol, Ph3P,
DIAD, THF, 0 °C to room temp, 12 h, 95-96%; (c) TFA, DCM, 12 h,
99%.
a Reagents and conditions: (a) TFA, DCM, room temp, 3-12 h,
98-100%; (b) methanesulfonic acid, dioxane, reflux, 2 h, 80-86%; (c) 12
N HCl, EtOH, 4 h at room temp, 6 h at 50 °C, 28-57%.
Scheme 4a
gave carbodiimide 9, which was in turn reacted with suitable
amines to give 10a,b, which after deprotection with trifluoro-
acetic acid furnished 11a,b as trifluoroacetates (Scheme 4).
Compound 15 was synthesized as reported in Scheme 5 from
the wholly protected guanidine 12 by alkylation, first with
cinnamic alcohol to give 13 and then with protected aminobu-
tanol to give 14, which after deprotection under standard
conditions gave 15 as a free amine.
To obtain 19a,b and 20a,b, thiourea 2b was first alkylated
with piperidine and N-methylpiperazine to give 16a,b, respec-
tively (Scheme 6). Reaction of these intermediates with 4-N-
(tert-butoxycarbonyl)amino-1-butanol and 6-N-(tert-butoxycar-
bonyl)amino-1-hexanol gave protected amines 17a,b and 18a,b,
which were then deprotected with trifluoroacetic acid to give
19a,b and 20a,b.
a Reagents and conditions: (a) p-fluorophenyl isothiocyanate, DCM, 12 h,
85%; (b) 2-chloro-N-methylpyridinium iodide, DIPEA, DCM, 12 h, 90%;
(c) suitable amine, isocyanate resin, toluol, 50 °C, 4 h, 90-99%; (d) TFA,
DCM, 3-12 h, 90-99%.
All compounds were evaluated in vivo in the widely used
diabetic db/db mice, characterized by a defect in the leptin
receptor, inducing hyperphagia, obesity, hyperglycemia, hyper-
insulinemia, and insulin resistance. Administration was per-
formed in male mice twice a day for 4 days and once on day 5,
by subcutaneous route, to overcome, in this first investigation,
any possible interference in adsorption and gastrointestinal
stability due to structural differences between the compounds.
On day 5, 8 h after last administration and in postabsorptive
conditions, improvements of glucose homeostasis, glucose
tolerance, and insulin sensitivity were evaluated using the insulin
suppression test (IST) of Greenfield et al.,7 as modified for
diabetic obese mice8 and slightly further modified (somatostatin
was substituted for propranolol and epinephrine,9 and blood was
withdrawn 60 min after the load injection, having verified that
at this time nearly steady-state plasma glucose and insulin levels
were reached). Values at time 0 can be viewed as postabsorptive
glucose levels. All the investigated molecules were given at
doses equivalent to 25 mg/kg 1a, while the antidiabetic drugs
metformin and rosiglitazone, used as reference compounds, were
administered in the same way at the respective doses, as reported
below. There was a significant reduction of glycemia with
respect to control for 1a (-31%), accompanied by a 53%
reduction of water consumption and about a 20% reduction in
food intake, while there was only a 13% reduction in glycemia
with 1b, together with a similar water consumption but a higher
(-37% vs control) reduction of food intake with respect to 1a.
During the investigation of the effects of the alkyl chain length
between amine and guanidine groups, the best antihyperglycemic
effect was produced by the six-carbon chain while the five- and
four-carbon chains (1m and 1b, respectively) seemed to be
endowed with the highest reduction in food intake. When the
double bond of the unsaturated alkyl substituent was replaced
by the corresponding saturated moiety, as in 1q, the activity
Scheme 5a
a Reagents and conditions: (a) Ph3P, DIAD, cinnamic alcohol, THF, 0
°C to reflux, 12 h, 74%; (b) Ph3P, DIAD, 4-(N-Boc)aminobutanol, THF, 0
°C to reflux, 12 h, 29%; (c) cyclohexene, 10% Pd/C, MeOH, reflux, 8 h,
88%.
Amines 4a-t were obtained by alkylation of intermediate
3a with suitable Boca-aminoalcohols (intermediates 4c,d) or by
reaction of 2b or 3b-f with different amines (intermediates
4a,b,e-t) (Scheme 2).
Deprotection of 4a-t with TFA, HCl, or CH3SO3H gave the
final compounds 1a-t as corresponding salts (Scheme 3).
Compounds 1s and 1t are two- and three-carbon superior
homologues of agmatine.
Compound 6 (see Table 1) was synthesized starting from 4n
by standard bromination with CBr4 in the presence of PPh3,
followed by deprotection with methanesulfonic acid.
Compounds 11a,b, having three substituents on guanidine,
were synthesized starting from Boc-protected 1,6-hexamethyl-
enediamine 7 and p-fluorophenyl isothiocyanate to give thiourea
8. Reaction of the thiourea with Mukaiyama’s reagent readily
a Abbreviations: Boc, tert-butoxycarbonyl; TFA, trifluoroacetic acid;
DIAD, diisopropyl azadicarboxylate; DCM, dichloromethane; DIPEA,
diisopropylethylamine.

Letters
Journal of Medicinal Chemistry, 2008, Vol. 51, No. 11 3075
Table 1. Reductions of Glycemia Levels at IST and of Cumulative Water and Food Intake, after 5 Days of Treatment in Male db/db Mice (4-6 per
Group)a,b
a All compounds were administered subcutaneously twice a day at doses equivalent to 25 mg/kg 1a. Values are expressed as % variation with respect to
control. For clarity, the chemical structures are drawn without counterions, and only the data of active compounds are reported. Student’s t test indicates (2)
p < 0.05, (0) p < 0.02, (9) p < 0.01, and (4) < 0.001 vs control diabetic mice. b For water and food intake, statistics were not applied, as the reported data
are the result of cumulative measurements of 4-6 animals per cage. Animals were observed daily throughout the experiment, exhibiting no modifications
in the general state of health or behavior.
was partially retained, but when a cyclopropylmethyl group was
introduced, an even stronger activity was found, 1e giving a
42% reduction in glucose blood levels, accompanied again by
a lower water and food intake (-45% and -19%, respectively).
The absence of substituents on the guanidine group led to
inactive compounds (1s and 1t). Introduction of a cyclohexyl
moiety in place of the linear alkyl chain in 1h, leaving the rest
of the structure unaltered with respect to 1e, resulted in good
antihyperglycemic activity, -29% in blood glucose levels and
a 40% reduction in food intake. We observed an even stronger
reduction in glycemia with respect to controls (-43%) 60 min
after IST, and water consumption (-59%) reflected the observed
efficacy. The trans-cyclohexyl analogue 1r had almost no effect,
suggesting stereochemical implications in the interaction of these
molecules with their unknown target(s). The activity was instead
at least partially maintained with derivative 1j, where the
cyclohexyl moiety was directly linked to the amine and
guanidine groups, and with 1i, both carrying the dimethylallyl
residue, as in 1a. Substitution of the amino group of 1e with a
bromine, hydroxyl, or methyl group, as in 6, 1n, or 1o,
respectively, led to less active (6) or almost inactive compounds,
indicating the importance of the original aminic functionality
(only food intake appeared moderately reduced (-20%) in the
methyl and bromine derivatives). Substitution of the dimethyl-
allyl fragment with different moieties in 1f, 15, and 19a,b
(derivatives of aminobutylguanidine) and in 11a,b and 20a,b
(derivatives of aminohexylguanidine) led to lower or no activity.
It is worth noting that the effect of metformin, when adminis-
tered twice a day in the same way, was modest and not
statistically significant even at high doses (glycemic reduction
of -11% at 13 mg/kg and -22% at 130 mg/kg), suggesting
that besides the apparent first-view structural similarity, different
mechanism(s) may actually be operating. Rosiglitazone, on the
other hand, administered with the same modality at 5 mg/kg
produced a glycemic reduction similar to that of our active
compounds (-29% and -39%, p < 0.05, at 0 and 60 min after
IST, respectively) with a corresponding reduction of water intake
of about 52%.
In conclusion, several substituted aminoalkyguanidines were
synthesized and tested, identifying a series of compounds with
an interesting profile as potential antidiabetic and/or antiobesity
drugs. The N-(cyclopropylmethyl)-N′-(4(aminomethyl)cyclo-
hexylmethyl)guanidine 1h appears to be the most balanced
antihyperglycemic and food intake-modulating compound. The
possibility of controlling glycemic levels and food intake appears
particularly attractive, also considering that among the currently
approved antidiabetic therapies only metformin and exenatide
appear to have a moderate but positive impact on body weight
while glitazones induce a further increment. Additional studies
on the pharmacology of the described compounds for an
evaluation of their mechanistic and pharmacokinetic properties
and for a deeper investigation of their activity profile as
antidiabetic and food intake-reducing agents are thus warranted.
Supporting Information Available: Experimental details and
analytical data for listed compounds. This material is available free
of charge via the Internet at http://pubs.acs.org.
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