BPAP

BPAP, short for 1-(benzofuran-2-yl)-2-propylaminopentane (benzofuranylpropylaminopentane), is a synthetic, tryptamine-derived compound designed as a "catecholaminergic/serotoninergic activity enhancer." Knoll and colleagues at Semmelweis University developed it with researchers at Fujimoto Pharmaceutical, as part of the selegiline line of research: after selegiline and (-)-PPAP showed the enhancer effect, the team changed the aromatic ring of PPAP, made 65 compounds and selected (-)-BPAP (Knoll et al., 1999; Yoneda et al., 2001).

The identity data are PubChem's for R-(-)-BPAP (CID 9816303), the form used in the published studies; X-ray crystallography confirmed its R configuration (Oka et al., 2001). Formula and weight are for the free base, while many studies used the hydrochloride. In PubChem, "BPAP" alone resolves to bisphenol AP, an unrelated chemical, so search by CAS number.

Published work on BPAP falls into five areas, each with its model. All of it is cell, brain-tissue or animal research, and PubMed lists no human trial. Most papers come from the Semmelweis group or include Fujimoto Pharmaceutical authors.

The activity enhancer concept

Knoll's group used "enhancer" for a compound that increases the transmitter release triggered by nerve impulses, and named the trace amines beta-phenylethylamine and tryptamine as natural examples. In the isolated rat brain stem, BPAP increased stimulation-evoked release of [³H]-noradrenaline and [³H]-dopamine at 0.18 micromolar and of [³H]-serotonin at 36 nanomolar (Knoll et al., 1999). Uptake inhibitors, MAO inhibitors and dopamine agonists did not reproduce this in the same preparation, which the authors took as evidence of a separate mechanism (Miklya and Knoll, 2003). Model: isolated rat brain stem.

A bimodal concentration-response

BPAP's effects often follow two bell-shaped curves. In rats that received 0.0005 mg/kg BPAP subcutaneously, the locus coeruleus removed 30 minutes later released more noradrenaline (15.4 versus 4.7 nmol/g in controls), while 0.05 mg/kg had no effect. In the organ bath, release peaked at 10^-13 M, had no effect at 10^-10 M and peaked again at 10^-6 M (Knoll et al., 2002). Model: rat locus coeruleus, in vivo and ex vivo.

Cells showed the same two ranges. After hypoxia and reoxygenation, BPAP protected rat PC12 cells and human brain capillary endothelial cells at femtomolar to picomolar concentrations and again at micromolar ones (Denes et al., 2006). In rat striatal slices, its effects on stimulated dopamine and GABA release were bell-shaped across 10^-13 to 10^-11 M (Harsing et al., 2025). Models: cultured cells and rat brain slices.

TAAR1 and other proposed targets

In 2002 the Semmelweis group suggested that the enhancer sites might be trace amine receptors (Knoll et al., 2002). Later, in rat striatal slices, BPAP increased stimulation-evoked vesicular [³H]-dopamine release without the non-vesicular release that methamphetamine causes, and EPPTB, a selective antagonist of trace amine-associated receptor 1 (TAAR1), blocked the effect (Harsing et al., 2022). A 2025 study repeated the block and called BPAP a potential TAAR1 agonist (Harsing et al., 2025). The 2022 study reports support from Fujimoto Pharmaceutical. Model: rat striatal slices.

BPAP also acts on transporters. In HEK 293 cells expressing human transporters, it inhibited dopamine, noradrenaline and serotonin uptake (IC₅₀ 42, 52 and 640 nM), and in rat synaptosomes it inhibited tyramine-induced noradrenaline release and did not increase release on its own (Shimazu et al., 2003). Models: transfected human cells and rat synaptosomes.

Rodent behavior

In the shuttle box, BPAP was about 130 times more potent than selegiline at countering tetrabenazine-induced inhibition of performance in rats (Knoll et al., 1999). BPAP hydrochloride raised locomotor activity in non-habituated rats across 0.3 to 10 mg/kg, reversed reserpine-induced hypolocomotion and increased ipsilateral turning after one-sided 6-hydroxydopamine lesions; the D1 antagonist SCH 23390 blunted the locomotor effects (Shimazu et al., 2001). With radiolabeled BPAP, brain radioactivity peaked 30 minutes after subcutaneous delivery, and radioactivity had an elimination half-life of 5.5 to 5.8 hours (Magyar et al., 2002). Model: rats.

BPAP reduced cue- and drug-primed reinstatement of methamphetamine seeking in rats without reinstating seeking on its own (Hiranita et al., 2010). In aged rats followed from 27 months of age, it had no effect on the age-related decline in task performance (Ernyey et al., 2024). Model: rats.

Neuroprotection and neurotrophic factor models

BPAP protected cultured hippocampal neurons from beta-amyloid toxicity at 10^-14 M (Knoll et al., 1999). In human SH-SY5Y neuroblastoma cells exposed to N-methyl(R)salsolinol, a dopaminergic neurotoxin, some BPAP analogs reduced apoptosis, with effects that depended on stereochemistry: R-enantiomers, including R-(-)-BPAP (FPFS-1169), induced Bcl-2 and prevented apoptosis more potently than the S-enantiomers, while dextrorotatory compounds stabilized mitochondrial membrane potential and levorotatory ones, the group that includes (-)-BPAP, did not (Maruyama et al., 2004). Models: cultured neurons and a human cell line.

Mouse astrocytes responded only at high concentrations. BPAP raised their NGF, BDNF and GDNF synthesis, with lowest effective concentrations of 1 to 50 micromolar and single bell-shaped curves peaking at 0.1 to 1 millimolar; NGF, tested down to 10^-15 M, showed no low-concentration effect (Shimazu et al., 2003). Model: mouse astrocyte culture.