Taste Enhancers and Blockers 01/30/21 “To Me, Life Without Veal Stock, Pork Fat, Sausage, Organ Meat, Demi-Glace, Or Even Stinky Cheese Is a Life Not Worth Living.”

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Baran Lab Cheng Bi Group Meeting Taste Enhancers and Blockers 01/30/21 “To me, life without veal stock, pork fat, sausage, organ meat, demi-glace, or even stinky cheese is a life not worth living.”

“I’ve long believed that good food, good eating, is all about risk. Whether we're talking about unpasteurized Stilton, raw oysters or working for organized crime 'associates,' food, for me, has always been an adventure.” In 2020, over 200 million people in USA consumed HEINZ® ketchup, the total annual sale is over 20 billion dollars. It occupies over 60% of the entire ketchup market in USA.

Natural Flavor?

Inorganic salts? Peptides? Anthony Bourdain (1956-2018) Steroids? Glycogen? Organic bases? Fatty acid?

O OH Theogallin Me Me HO OH Me H O NH O S N OH 2 H Me OMe O N Me HO N O OH H Me O Me Sucrose Capsaicin HO OHO (table sugar) OH Alitame Umami—savory > 2000 times sweeter Chili Pepper Is it a taste? O OH HO OH OH O O HO O O N H HO Succinic acid MeO Me H OH O H H HO N Cinchona Tree O OH isolated in 1820 O Quinine HO O OH aganist malaria Intensify saltiness Aldosterone Adipic acid Tartaric acid Baran Lab Cheng Bi Group Meeting Taste Enhancers and Blockers 01/30/21

Before 1910s, people generally believed that there were 4 types of basic tastes the O O combinations of which could lead to a variety of flavors in dishes. Those four basic are sweet, salty, bitter and sour. In 1907, Professor Ikeda from Tokyo Imperial University noticed Na+ HO O- that something in “dashi” made the dish extremely savory. One year later, he isolated a slightly brown crystal from “dashi” which he believed was the source of the savory taste and NH2 named it “Ajinomoto”—the essence of flavor. The discovery of monosodium glutamate is Monosodium glutamate also the discovery of the fifth basic taste—“umami”. (MSG) Chemical synthesis Extraction Fermentation ~ 2 million tons / year 1909-1962 1962-1973 currently O O CO, H2 O NH4CN NH2 NaOH, H2O NC HO O- oxo reaction NC H Strecker NC CN + Ajinomoto ~ 2 ¢/ml NH Na 2 Kikunae Ikeda (1864-1936) “essence of flavor”

Taste signals are eventually received and processed in gustatory cortex.

Type 2 Type 1 Type 3 (GPCRs) The primary organ for taste sensation— Salty Sweet, bitter and umami Sour oral cavity. Taste Mostly activated by Activated by a large variety of Mostly activated by receptor cells (TRCs) inorganic salts and adjust organic molecules ans use protonic acids and can are mainly located in ion concentrations intra- ATP as the signal transmitter. accumulate cations in taste buds. and extracellular. the cells. Baran Lab Cheng Bi Group Meeting Taste Enhancers and Blockers 01/30/21

Nowadays, it is generally accepted that there are two types of salty taste receptors: epithelial sodium channel (ENaC) and transient receptor potential cation channel subfamily V member 1 (TRPV1). ENaC is cation-specific and selectively sensitive to Na+ and Li+ however TRPV1 is cation-nonspecific and can respond to a wide variety of + 2+ + cations (K , Ca , NH4 …) and even organic molecules.

Recommended daily NaCl intake is about 2.3 g

O Me Me N H one piece of patty one slice of pizza Me ~ 1.0 g NaCl ~ 1.2 g NaCl Spilanthol Taste enhancers: compounds that have no or little intrinsic taste but can significantly intensify one or Me several of the five basic tastes upon ingested. Positive allosteric modulators (PAMs): compounds that can bind to spots other than orthosteric spots O and trigger similar downstream biological Me reactions. N O OH H OH O NH O Me Me O O Me HO Na+ Me Sanshool O- OMe H2N N N R Me N H Me O NH2 H H OH NH2 H2N OH then Me Sodium aspartate Arginyl dipeptides NGCC (IFF) Methyl lactate Me3NO, MeCN EDC, HOBt r.t. DCM, r.t. R1 CN NaHMDS, THF (OC) Fe 1, DIBAL (OC)3Fe R = Ph P+Br- 3 o 1 3 0 oC → r.t., 90% toluene, -20 C O

Fe (CO) CN 2. (EtO)2POCH2CO2H 3 12 Fe(CO) toluene 3 Me r.t., 75% Me OH R CN Me CHO 2 reflux, 80% KHMDS, THF (OC) Fe 1, DIBAL O Me CHO 3 o (OC)3Fe 2,4-hexadienal -78 oC → r.t., 74% CN toluene, -20 C O OH O N N S 2. (EtO)2POCH2CO2H R2 = Me r.t., 70% N N Me Ph Tet. Lett. 2012, 6000; Chemical Senses 2019, 91 Baran Lab Cheng Bi Group Meeting Taste Enhancers and Blockers 01/30/21 OH HO Amberlite 15 L-alanine Br2, MeOH O H o BuOAc/H O NaOH, H2O CO2H H2O, 0 C → r.t. 2 HO HO N HO OH N HO CHO then Ni/H O OH O 2 Me OH J. Agric. Food Chem. 2003, 4040 Me CO2 Hexose Maillard reaction: see Food Chemistry (Baranlab GM by David Peters in 2019) Alapyridaine Stewed beef OH OH Preliminary SAR study HO HO N Me N OH N

Me CO2 Me CO HO CO 2 N 2 inactive bitter OH OH O Me CO2 HO both the hydroxyl and hydroxymethyl N N HO the absolute configuration N O the carboxylate group Me CO Me CO A general taste enhancer? 2 2 Mol. Nutr. Food Res. 2004, 270 – 281 Me

The structural features of sweet and umami taste receptors

N-terminal extracellular domain (ECD) 7 transmembrance domains (TMD) cysteine-rich domain (CRD)

Orthosteric site (open to close)

Taste signal transduction mechanisms

sweet or umami tastants bind to VFD which transform to closed state C-terminal couples with Gα, Gβ or Gγ-gustducin proteins G-gustducin proteins stimulate phospholipase C-β2 (PLCβ2) PLCβ2 then hydrolyzes phosphatidylinositol 4,5-bisphosphate (PIP2) decomposition to diacylglycerol (DAG) and inositol triphosphate (IP3) IP3 activates IP3 receptors on endoplasmic reticulum (ER) Ca2+ is released into plasma and activates Na+ channel increased concentration of Na+ cause release of ATP into fibers signal is finally intercepted by gustatory cortex in brain Front. Pharmacol. 11:587664. Curr. Opin. Clin. Nutr. Metab. Care 2017, 279 Baran Lab Cheng Bi Group Meeting Taste Enhancers and Blockers 01/30/21 O O O O Na+ Widely used artificial sweeteners S K+ S O NH O N- O- HO H S HO N Me N Me O O OH O H Cl HO Me O Cl O Me Cyclamate 1998-2018 HN O Saccharin Acesulfame-K acquisted by Firmenich® NH HO O O OMe 2 Me O O O OH Cl O Me stablize closed form Sucralose Neotame N NH2 NO2 H P-4000 Dulcin sweet taste enhancer O H O H N N sweet tastant O H O S N O S N O S N N Me Me O NH2 NH2 O Me NH O N Me N SE-3 2 H N O Me S617 S2218 Me DBU NH2 o O O O 160 C → r.t. CN + S HCl/EtOH Me H2N NH2 0 oC → r.t. HO then DMF N EDC, HOBt O O Me NaH, THF S H NO O2N H2N O 2 NaH, THF Boc O H2N Cl N 2 O S Me o o → lutidine, r.t. H N CN -30 C → r.t. -60 C r.t. 2 + N OH NC Me Me NC Me Me Me then then Me Me O Pd, H 40 psi O o NO2 2 NaOH 115 C NH O NH2 NHBoc 2 O NHBoc

N C O H H H S, Et N NaOH, 100 oC O N 3 H2N S Ph N N S O EtOH, 80 oC S H O/EtOH Me 2 Me NC CN + Me Me N Me O O NC Dioxane, r.t. NC H2O/AcOH 0 oC → r.t. Me Me Me NH2 S2383 Baran Lab Cheng Bi Group Meeting Taste Enhancers and Blockers 01/30/21 N O O N Preliminary SAR study O O Me Me HO NH2 N N the head structure is very important for efficacy HO H H the hydrophobic structure in tail is beneficial N N O NH H H 2 the the length of linker is also very important O NH2 NH2 Linker Bioorganic Med. Chem. Lett. 2020, 127000; ChemistrySelect 2020, 9457 Head Tail E% = 93±4.3 E% = 87±5.1 Common umami tastants Common enhancers: nucleotides O N O O O O O HO O O N OH N HO O Me HO P O N O OH OH HO OH HO O P NH HO O Me NH O NH NH N 2 2 2 O Me HO OH N NH HO OH L-Leucine Aspartic acid Glutamic acid Maltol NH2 guanosine monophosphate inosine monophosphate MeO OMe Br MeO OMe 1.carbodiimide MeO OMe HN N 2.thiosemicarbazide O aq. NaHCO N O 3 N NH HN NH2 S N HN N EtOH, heat OH S N MeO OMe S H WO 2006/084186 A2 FEMA 4798 In 1993, the first specific inhibitor for bitter taste was discovered. It is a lipo-protein made of phosphatidic acid (PA) and β-lactoglobulin (LG). Taste blockers: compounds that have no or little intrinsic taste but can dramatically inhibit the sensation of one or multiple of the five basic tastes.

OH O O O H2N OH H2N N OH 4-Aminobutanoic acid HO O N︎,N︎-bis(carboxymethyl)-L-lysine With the assistance of computational model, the aforementioned two compounds that have similar binding to bitter receptors as quinine should Nature. 1993, 213; Brain Research Protocols 1997, 292 be potent bitter inhibitors. Indeed, biological experiments proved that. J. Biol. Chem. 2014, 25054; Protein Expr. Purif. 2010, 85 O Ph PCHCO Et Me2CO, NaHCO3 ZnBr2, PhMe 3 2 Me KOtBu, 0 oC → r.t. Bull. Chem. Soc. Jpn. 1995, 89 Oxone, H2O O reflux Me OH Synlett. 2004, 2633 Me Me O Me Me Me Pd, H2, r.t. Me Current Biology 2010, 1104 Me Me Me Me then NaOH, HCl GIV3727 Baran Lab Cheng Bi Group Meeting Taste Enhancers and Blockers 01/30/21 OMe Bitter taste blockers F Bitter tastant OH the hydroxyl groups on A ring have OH O O O strong H-bonding the planar C ring has better HO O MeO MeO docking with recpetors MeO the substituents on B ring have O O minor effects on bonding O OH O Luteolin PLoS ONE 2014, 94451; PLoS ONE 10(3):e0118200

OH Ar OH OH O Ar Oxidant; Condensation Mitsunobu Asymmetric Michael Ar Ar inversion reduction O Ar O Ar O O O O OH O

OH OH O OH Ar O Ar O Epoxide 1,4 addition Ar Asymmetric Asymmetric opening 1,4 addition oxy-Michael O O Synth. Commun. 2013, 3093 O O Eur. J. Org. Chem. 2012, 449 O

O CO2Me 1 eq BF •Et O O I 1.5 mol% Pd2(dba)3 CHO 3 2 H 3 mol% PA-Ph DCE, 50 oC CO Me + + 2 R 1 atm CO, DBU OH o Me2N DMF, MW, 90 C O R OMOM O Org. Lett. 2009, 3210 Tetrahedron. 2013, 647 Abscisic acid Me Me Me Me Me Me Me Me Me O Me Me O Me Wittig CHO O3 Aldol Me N OH OH OH OH O CO2H O Me O Me O Me O Me Me O Biochemistry 2015, 2622 Tet. Lett. 1989, 1741 Me

Me Me t-BuOOH Me Me Swern [O] then Me Me Me Me Me Me Me p-TsOH, benzene Ti(Oi-Pr)4 Triton B, THF OH OH CO2Et reflux (-)-diethyl tartrate KOH then HCl CO H + O O O 2 OH then LAH Me Me MeO2C CO2Me CO2H O Me OH OH Me O Me O O Me Me Me Me Me ACS Omega 2020, 13296 Baran Lab Cheng Bi Group Meeting Taste Enhancers and Blockers 01/30/21 H N O OH O O O O O HO HO OH OH HO Me OH HO OH OH O O OH Acetic acid Citric acid Fumaric acid Malic acid NH2 Serotonin Two general hypothesis exist as to the mechanism of sour taste perception. The first assumes extracellular absorption of acidic stimuli, while the second presumes penetration of sour taste stimuli into the cell. H H2N N CO2H H H2N N CO2H O NH O N Biosci. Biotechnol. Biochem. 2015, 171 Overcooked food (meat) to give a thick-sour taste? J. Food Sci. 2007, 33; J. Agric. Food Chem. 2009, 9867

OH OH OH OH OH O NH H HO O 2 NH O O H O heat N heat O OH H O P OH H O N N HO N N O + OH O N OH decomp. N HO Maillard N N OH N Me O Me OH N N N Phosphocreatine Creatinine Hexose Me Me J. Agric. Food Chem. 2011, 8366; J. Agric. Food Chem. 2010, 6341 Me Sour taste enhancers

Me HN KOtBu, THF H H H N N SO2Cl2 N Cl NaH, THF H 0 oC → r.t. N S SH S Me DCM, r.t. then NH N OMe O N N S O 3 Me H2O/EtOH OH N O CF3 Me N m-CPBA O + 0 oC → r.t. NaOEt CN 108947967 A o O CF3 HC. 2008, 363 Me THF, 0 C Proton-pump Inhibitor (PPI) CHO + HO CF3 H2O2 N Irreversibly blocking the O CHO H AcOH N hydrogen/potassium adenosine N O HNO Me N H [O] S triphosphatase enzyme system 3 N + + Me N H2SO4 N OMe O (the H /K ATPase) a n d Cl + SH + suppressing the secretion of H Me Me O N CF3 Lansoprazole in digestive system. Me NO2 CF3