Investors are flocking to one of the first offerings of digital tokens done under the U.S. securities regulations.

Venture-backed startup Protocol Labs Inc., which intends to develop a distributed data storage system called the Filecoin Network, has raised $52 million in a first tranche of the offering, according to Protocol founder Juan Batiz-Benet.

Participating investors, including Winklevoss Capital, Digital Currency Group and Y Combinator’s Sam Altman, bought securities that entitle them to obtain the Filecoin tokens.

“We invested in Protocol Labs in 2014 and have been following its progress closely,” Tyler Winklevoss, co-founder of Winklevoss Capital, said in an email to WSJ Pro Venture Capital. “We invested in the Filecoin Network because we believe in its underlying technology and tremendous promise.”

In recent months digital token sales, also called initial coin offerings, have become a high-profile fundraising method for startups and others. The groups raising capital create digital tokens that have a value and can be exchanged for other currency and that are also useful in software products. Such sales usually don’t represent equity, but the Securities and Exchange Commission served notice in July that some digital tokens could be considered securities subject to regulatory supervision.