Pyripyropene ©

1. Discovery, producing organism and structures1-6)
Pyripyropenes were isolated from the culture broth of the fungal strain FO-1289 and found by anenzyme assay to be inhibitors of acyl-CoA:cholesterol acyltransferase (ACAT). The structures
were elucidated by spectral analysis, including NMR3,5). The relative and absolute stereochemistries were confirmed by NOE and X-ray crystallographic analysis for pyripyropenes A4) and E5).
Pyripyropenes have a common structure consisting of pyridine, α-pyrone and sesquiterpene moieties.

Aspergillus fumigatus FO-1289
Bar: 20 µm

2. Physical data (Pyripyropene A)3)
White powder. C31H37NO10; mol wt 583.24. Sol. in MeOH, EtOAc, CHCl3. Insol. in H2O, hexane.

3. Biological activity1,2,4,7-15,20,22,23)
1) Enzyme assay for ACAT inhibition1,2,7)
ACAT inhibitory activity (See also “Purpactin”) was tested in an enzyme assay using rat liver
microsomes. Pyripyropenes are the most potent ACAT inhibitors of microbial origin.
Compound

IC50 (µM)

CompoundPyripyropene ABCDEFGHIJ

0.058
0.117
0.0530.268
399559221
270
2.450.85

Pyripyropene KLM
NOPQR
CL-283,546*		IC50 (µM)
2.65
0.27
3.80
48.0
11.0
40.0
40.0
78.0
1.30

*Synthetic ACAT inhibitor having a urea structure7)2) Selectivity in inhibition of ACAT isozymes.
Recently two ACAT isozymes, ACAT 1 and ACAT 2, have heer identified in various mammals.
ACAT 1 is ubiquitous and is expressed more strongly in sebaceous glad, steroidogenic tissues
and macrophages, while ACAT 2 is expressed in the bver and intestine.
ACAT 1
PyripyropeneABCD>80
483238IC50(nM)

ACAT 20.07
2.00.36
1.5

Cell-based assays were established by using ACAT 1- and ACAT 2- expressing CHO cells toevaluate the selectivity of ACAT inhibitors toward the two isozymes. Pyripyropenes were foundto be the first inhibitors selective toward the ACAT 2 isozyme. In particular, pyripyropene A
shows the highest selectivity among ACAT inhibitors so far reported. Research for more potent
and selective pyripyropene derivatines is extensively studied for development of a new type ofanti-atheroscrelatie agents.
3) Structure-activity relationship8-12)
Comparison of ACAT inhibitory activity among natural pyripyropenes and synthetic derivatives8-12) revealed the structure-activity relationship. A proposed model for binding of a derivative
PR-109 to ACAT is shown below.
OO

CH3

CH3ONHOCH3O

H

HOO

O
CH3

PR-109Inhibition of [ 3H]cholesterolabsorption (%)4) In vivo evaluation4)
In vivo efficacy of pyripyropene A and synthetic derivatives were evaluated in a hamster model.
PR-86 showed more potent inhibition of cholesterol absorption from the intestines (ED50, 10 mg/kg) than pyripyropene A (ED50, about 100 mg/kg).
100
PR-86

80

PR-10960

OCH3CH3OOH3C

pyripyropene ACH3O

10Dose (mg/kg)

O

100

HO

H
O

1N

HO

40
20O

SO
CH3PR-86

OCH35) Inhibition of multidrug resistant P-glycoprotein by a semi-synthetic analog of pyripyropene.14,15)
7-O-Benzoylpyripyropene (7-O-BzP) (6.25 µg/ml) effectively reverses P-glycoprotein-related
MDR by interacting directly with P-glycoproteins in drug resistant VJ-300 and P388/ADR cells.
4. Biosynthesis of pyripyropene A16,24,25)
Incorporation of 13C-labeled precursors and degradation experiments revealed that a nicotinicacid primer condenses with two acetates in a head-to-tail fashion forming the pyridino-α-pyrone
moiety, which is linked with a sesquiterpene forming the core skeleton. Then, three acetyl residues are introduced into the core. This is the first demonstration that an intact nicotinic acidworks as an acyl primer unit for oligoketide formation in fungal secondary metabolites.
The biosynthetic gene cluster for pyripyropene was identified and the biosynthetic enzyme activities were demonstrated.
CH3COONa■X 14●OX 5■HO●HOOOH■●O■●HOX 3OH■

O

●

●

■

OO■

●

▲

■
■
●
■

O

■
●
■

●
■
●

●
■
■
●
■

O
●

OON▲
■

O
●

■

N

5. Total synthesis17,18,21,26)
The total syntheses of pyripyropenes have been reported by several groups. The following
scheme is Ōmura’s approach.17) (See Appendix-I).
1) Ethylene glycol,
1) pp-TsOH
2) aq. HCHO, PhSH,
1) Et3N, EtOH
3) Li, NH3, tt-BuOH,
1) HCHO, THF

O(40%, 2 steps)O

O O
AcOH, CH3CN
(95%)

HHO1)

O

BnO

CO2Me

BnO

(99%)

BnO

H

AcO

(96%, 3 steps)

OH

H

COCl(COCl)2, (14 equiv.),2 h; remove (COCl) 2O
O

O

H

AcO

O
OAc

TFA
(47%)

O
H
AcO
AcO

O
NaBH4, MeOH,CeCl3•7H2O

O

N

HOO

(96%)

H
AcO
AcO

H

OAc

Pyripyropene AO

N

OH

AcO

H

BnO

BnO

NaH (1.05 equiv.),
PhH, r.t., 2 h;

OAc

BnO

1) H2, Pd(OH)2, MeOH
2) NaH, PrSH, DMF
3) Ac2O, Pyr., DMAP

CO2MeBnO
CO2H

CO2Met-Bu

NaBH4, MeOH,CeCl3•7H2OO

HN2) Pd(OAc)2, CO, PPh 3,2) Et3N, MeOH, DMF(62%, 2 steps)

H

BnO(66%, 2 steps)

t-Bu

Tf2O, CH 2Cl2

BnO
1) SeO2
Dioxane,2) PCC, PhH
Celite, 3A MS(85%, 2 steps)

H

CH3(66%, 2 steps)

H

AcOHOHO
1) KDA, THF
1) TMSCl, Et3N2) BTSF, MeI
1) 4A MS, THF

O1) NaH, BnCl, THF
2) 2N HCl, THF

Me4NBH(OAc)3Os(S)-(+)-W.M.K.

BnOO O

Overall yield 3.7 % in 18 steps

HOAcN6. References
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24.		
T. Itoh et al., Nat. Chem. 2, 858-864 (2010)25.		
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