Eserethole

Eserethole is a nitrogen-containing organic compound (C₁₅H₂₂N₂O). It possesses a unique bicyclic structure, combining an indole and a pyrrole ring system. It is used in the synthesis of various alkaloids.^[3]

Eserethole

Names
IUPAC name (3aR,8bS)-7-ethoxy-3,4,8b-trimethyl-2,3a-dihydro-1H-pyrrolo[2,3-b]indole
Other names Eserethol (-)-Eserethole Pyrrolo(2,3-b)indole, 5-ethoxy-1,2,3,3a,8,8a-hexahydro-1,3a,8-trimethyl-, (3aS,8aR)-
Identifiers
CAS Number	469-23-8
3D model (JSmol)	Interactive image Interactive image
ChemSpider	9054687
PubChem CID	10879418
UNII	IP09BY41GA
CompTox Dashboard (EPA)	DTXSID701135279
InChI InChI=1S/C15H22N2O/c1-5-18-11-6-7-13-12(10-11)15(2)8-9-16(3)14(15)17(13)4/h6-7,10,14H,5,8-9H2,1-4H3/t14-,15+/m1/s1 Key: KQWOEHQIZVGMMT-CABCVRRESA-N
SMILES CCOC1=CC2=C(C=C1)N(C3C2(CCN3C)C)C CCOC1=CC2=C(C=C1)N([C@@H]3[C@]2(CCN3C)C)C
Properties
Chemical formula	C15H22N2O
Molar mass	246.35 g/mol
Appearance	Red to Dark Red Semi-Solid[1]
Solubility	Chloroform (Sparingly) Ethanol (Slightly)[1]
log P	1.5[2]
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Infobox references

Discovery

Discovery of eserethole is associated with a scientific competition in the 1930s. Two research groups were independently trying to synthesize the drug physostigmine. One group, led by Percy Julian at Howard University aimed to create d,l-eserethole as a crucial intermediate step. Another group, working under Sir Robert Robinson also reported the synthesis of d,l-eserethole around the same time.

However, the d,l-eserethole reported by Julian's group exhibited entirely different properties compared to that of Robinson's group. Ultimately, eserethole synthesized by Julian's group was proved to be the actual compound based on melting point equivalence with eserethole obtained from natural sources.^[4][5][6][7]

Properties

Eserethole is not an end product itself, but rather a molecule formed during the synthesis of other compounds, particularly alkaloids found in Calabar bean.^[8]

It exists as a red to dark red semi-solid and is usually stored at 253K under inert conditions. It is sparingly soluble in non-polar solvents like chloroform and slightly soluble in polar solvents like ethanol.^[3]

Eserethole contains a pyrrolo-indole aromatic ring system with a pyrrole ring attached to a indole ring. It has two stereocenters.

Uses

Eserethole is a vital building block in the synthesis of physostigmine, a naturally occurring alkaloid and acetylcholinesterase inhibitor used to treat glaucoma and delayed gastric emptying.^[9][10]

It is also intermediate in the synthesis of other alkaloids with acetylcholinesterase-inhibiting properties like (-)-physovenine, (-)-geneserine, etc.^[8]